- Email: [email protected]
Excellent energy density of crystalline SrTiO3@Amorphous Al2O3 nanocomposite combined with electrode-induced interfacial reaction
Journal of Alloys and Compounds xxx (xxxx) xxx
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Excellent energy density of crystalline SrTiO3@Amorphous Al2O3 nanocomposite combined with electrode-induced interfacial reaction Wei Bi a, Manwen Yao a, *, Wenbin Gao b, Zhen Su a, Xi Yao a a
Functional Materials Research Laboratory, School of Materials Science and Engineering, Tongji University, Shanghai, 200092, China Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education & International Center for Dielectric Research, Xi’an Jiaotong University, Xi’an, 710049, China b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 4 August 2019 Received in revised form 25 November 2019 Accepted 26 November 2019 Available online xxx
Simultaneously enhancing the breakdown strength and the dielectric constant is considered as a trend in material design for increasing energy density of linear dielectrics. Based on this point, crystalline SrTiO3 nanoparticle@amorphous Al2O3 composite film (Au top electrode) is prepared via spin coating process with dielectric strength of 118.1 MV/m and dielectric constant of 23.6. Further, under aluminum top electrode, higher breakdown strength of 342.9 MV/m and superior energy density of 12.2 J/cm3 are realized, which is stemmed from anodic oxidation reaction at the interface between the aluminum electrode and the composite dielectric film. This new composite structure shows an improved energy density, which provides a feasible avenue to design excellent inorganic dielectric composites assimilating the high breakdown strength of amorphous structure and high dielectric constant of crystalline dielectrics. © 2019 Elsevier B.V. All rights reserved.
Keywords: Composite dielectric film Dielectric constant Breakdown strength Energy density Interface modification Anodic oxidation
1. Introduction Developing energy storage technologies is one of the most promising options to solve the serious energy shortage problem in 21st century and meet the ever-increasing energy requirements [1e3]. Among various available electrical energy storage devices, dielectric capacitor plays a vital role in high-power density applications owing to its ultrafast charging-discharging rate and high operating voltage [4e6]. But there is still a challenge for improving its energy density. The energy density (U) of dielectric capacitor is determined by the applied field (E) and the electric displacement (D), given by U ¼ !EdD. For liner dielectrics, it can be defined as following: U ¼ 1/ 2DEb ¼ 1/2ε0εrE2b, where ε0 is the vacuum dielectric permittivity (8.854 1012 F/m), εr is the relative dielectric constant and Eb is dielectric strength [7]. Therefore, a high dielectric strength and a large dielectric constant are required. However, traditional dielectric materials are ceramics with large dielectric constant but small breakdown strength. New developed polymer dielectric materials embrace relatively high electric breakdown field but short of
* Corresponding author. E-mail address: [email protected] (M. Yao).
dielectric constant value [8,9]. Researchers widely studied many types of materials and provided one relationship based on theory and experiment: Eb ~ ε-½ [10], which means a limitation for achieving high breakdown strength and giant dielectric constant simultaneously in one material. Hence, tremendous efforts have been made towards material recombination, micro-structure design, and process innovation in order to achieve optimal relationship between two key parameters and explore new dielectric materials with great energy density. For example, (a) introducing inorganic material of large dielectric constant, as TiO2, BaTiO3, SrTiO3, Pb (Zr, Ti) O3 etc., into polymer dielectric matrix with high breakdown strength [11e15] and adding nano particles into amorphous dielectric film to improve its properties based on nano effect [16]; (b) controlling the 3D distribution and orientation of oxide nanoparticles in a polymer matrix to resolve the paradox between dielectric constant and breakdown strength [17] and changing the nanostructure of additions to accomplish complication of breakdown path then to increase final breakdown strength [18]; (c) with requirement of complex design for dielectric material, applying different methods such electrospinning, tape-casting, traditional ceramic techniques and so on combined with dispersants or surfactants to investigate promising dielectrics [12]. Clearly, composites, microstructure design and technical
https://doi.org/10.1016/j.jallcom.2019.153196 0925-8388/© 2019 Elsevier B.V. All rights reserved.
Please cite this article as: W. Bi et al., Excellent energy density of crystalline SrTiO3@Amorphous Al2O3 nanocomposite combined with electrodeinduced interfacial reaction, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.153196
2
W. Bi et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
improvement are research trends for exploring high energy density dielectrics with the breakdown strength and dielectric constant improved simultaneously. With great properties, linear dielectric capacitor is one most effective device for energy storage whose dielectric constant is independent of electric field. Aluminum oxide (Al2O3, abbreviated as AO) and strontium titanite (SrTiO3, abbreviated as STO) have been widely studied as representative of linear dielectrics. AO is a promising material for high energy density storage capacitors due to its high breakdown strength(300e700 MV/m),high band gap(~9 eV) and its chemical and thermal stabilities. However, comparing to other dielectric material, its dielectric constant (8.6e10) would be the limitation for improvement in energy density storage. STO with crystalline structure embraces a relatively high dielectric constant around 300, which is much higher than AO [19]. However, it is reported that mean dielectric strength of a STO single crystal is just 40 MV/m [20,21]. Thus, merging these two’s great properties provides a design idea for inorganic composite dielectrics, which holds a thermal endurance compared with organic dielectric composites. Several researches have been tried referring to this idea, such as SrTiO3/Al2O3 laminated film capacitors and nano-Al2O3 particles doped SrTiO3 composite films, exhibiting a great progress in dielectric strength [22,23]. In this work, a composite is designed combining large dielectric constant of STO crystalline nanoparticles and high breakdown strength of amorphous AO to accomplish development for energy density. The electrode materials would influence the electrical characteristics, which is another hotspot aimed to optimize dielectric capacitors [24e26]. For example, Yip et al. prepared thick Al2O3 insulator with Al electrode and found the leakage current and breakdown strength are strongly improved because of one likely mechanism based on ionization potential and diffusion coefficient [27]. To learn the effect of different electrodes on dielectric material, two kinds of top electrode, gold and aluminum, are adopted on this composite dielectric. In this study, complementary advantages of crystal SrTiO3 and amorphous Al2O3 have been merged to gain a superimposed effect, leading to a proper enhancement in both dielectric constant and breakdown strength. In order to achieve this composite film with structural integrity, ball milling blending process is applied combining with triethyl phosphate (TEP) as one effective dispersing agent. As the electrode material can help optimize the dielectric behaviors of the film, two kinds of top electrode are adopted. Under the Au top electrode, the composite dielectric film shows a good dielectric performance with dielectric strength of 118.1 MV/m and dielectric constant of 23.6. Compared to Au top electrodes, this composite film with Al top electrode exhibited great improvement in the dielectric strength to 342.9 MV/m, result in the energy density reaching 12.2 J/cm3. To better understand this improvement, one mechanism based on anodic oxidation reaction is proposed with relevant experimental evidences. A newborn AO layer with excellent dielectric strength is generated at the electrode-film interface to realize an interface modification for the composite film, which is the reason that the composite film with Al top electrode can embrace great dielectric properties. This work provides a new approach for designing high energy-density inorganic dielectric composites. 2. Experimental 2.1. Preparation A notable stable 0.04 M alumina sol was prepared by conventional sol-gel process. The details for the sol-gel process can be found in Ref. [28]. Then commercial STO powders (a mean particle
size of 151 nm) were added into the alumina sol. Moreover, a small amount of triethyl phosphate (TEP), as an organic dispersant, was added into the above solution to disperse STO nanoparticles in AO sol [29]. Wet-ball-mixing was applied for 24 h. Then the mixture was stirred for 3 h to form a stable composite slurry. Spin-coating was used to deposit the composite slurry or pure 0.04 M alumina sol onto the Pt/Ti/SiO2/Si substrate at 3000 rpm for 30 s. Here, we prepared 5-layer composite dielectric film. The first two layers were the composite slurry layers. Then 3-layer pure 0.04 M alumina sol was deposited on them, which was attempted to improve the roughness of the surface of the composite film to benefit for coating electrode further. Each layer was conducted with pre-heating process to remove the organics. When the deposition was finished, the films were annealed at 450 C for 3 h to obtain the final nanocomposite dielectric film. Then Al or Au top electrode with diameter of 1 mm was fabricated by ion sputtering for further measurements. In following discussion, for composite slurry with/ without organic dispersant (TEP), the samples were abbreviated as TEP-modified STO_nps@AO/STO_nps@AO. Fig. 1(a) is the process illustration for samples of nanocomposite dielectric film. Fig. 1(b) exhibits the structure of composite film by the SEM cross profile of (Al)TEP-modified STO_nps@AO as the representation. The total thickness for samples is about 1.5 mm. 2.2. Characterization The phase structure of nanoparticles and nanocomposite film was investigated by the X-ray diffraction (XRD, Rigaku D/max2550, Rigaku, Japan) patterns with an incident angle of 1. The microstructure of the composite and relative EDX analysis were learned using a high-resolution transmission electron microscope (HRTEM) (JEM-2011F). The microstructure morphology characterization and relative EDX analysis were measured with field emission scanning electron microscopy (FESEM, Philips XL30). Relevant electric tests, as current-electric field measurement, were performed by a computer-controlled voltage/current source (2400, Keithley, USA). Impedance spectroscopy to learn dielectric properties were carried out by precision impedance analyzer (Agilent 4294A). The discharge properties are studied through the chargedischarge platform (CFD-001) supplied by Gogo Instruments Technology Co. Ltd. 3. Results and discussion 3.1. The improvement of composite film structure with organic dispersant TEP To achieve a good microstructure of the composite film, organic dispersant TEP is used here to adjust the compatibility and dispersibility of the first two composite slurry layers. To learn about the TEP-modified effect on the elements’ distribution, mapping EDAX analysis of composite slurry layers’ surface is performed. According to the analysis (Fig. 2 (a1) and (b1)), STO nanoparticles can be more uniform distributed in aluminum sol in TEP-modified STO_nps@AO samples, reflected in a more even distribution of elements. The surface SEM pictures exhibit the micro-structure of the composite slurry layers. For samples without TEP, the alumina sol separating the STO particles turns into lots of nano-sized small alumina grains adhering around larger STO particles as shown in the close-up view in Fig. 2 (a2). On the contrast, STO particles can be firmly encapsulated by alumina sol after TEP modified, forming a compact and uniform surface structure as shown in Fig. 2(b2). The TEP can effectively improve the compatibility between STO powders and AO to achieve the composite slurry layers’ uniformity. TEP is one simple chemical structure phosphate ester surfactant
Please cite this article as: W. Bi et al., Excellent energy density of crystalline SrTiO3@Amorphous Al2O3 nanocomposite combined with electrodeinduced interfacial reaction, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.153196
W. Bi et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
3
Fig. 1. (a) Process illustration for samples of nanocomposite dielectric film. (b) Composite film structure exhibited by the SEM cross profile of (Al)TEP-modified STO_nps@AO.
effectively used in our research. Phosphate ester surfactant as a dispersant is widely used in traditional ceramic process [30]. K.R. Mikeska et al. detailed mechanism by which the phosphate ester disperses the barium titanite particles [31], which provides an idea to understand the dispersion effect of TEP for our research. The heating effect of high-speed ball-milling and the acid condition of the AO sol make TEP hydrolyze into diethyl phosphate, which would easily ionize to be an anionic surfactant. The anionic surfactant absorbed on the ceramic particle plays a wetting role, improving the compatibility. Besides, the structure of phosphate ester suggests a steric contribution and the dissociation of the diethyl phosphate contributes a diffuse layer of ions adjacent to the solid surface forming static hindrance, reducing the agglomeration of nanoparticles. In general, with TEP modification, the compatibility of two material and the dispersity of STO nanoparticle in AO sol are effectively improved, which lays a root for further study of this composite materials’ structure and performance. 3.2. Nanostructure and electrical properties of composite films Start with the materials’ structure, it can be clear to understand their characteristics. The XRD patterns of pristine STO nanoparticles, composite slurry layers, and composite film are displayed in Fig. 3((a) (b) (c)). Pristine STO are crystalline nanoparticles as perovskite structure of STO can be clearly found according to the standard PDF card (No. 73e0661) (Fig. 3(a)). For composite slurry layers (Fig. 3(b)), perovskite structure of STO is also distinct and no
AO peak could be found. Besides, in composite film of Fig. 3(c), for the samples’ surface is pure alumina layers, characteristic peaks of STO is attenuated but still no peaks for AO. It can be speculated that the AO are amorphous phase in composite film. The XRD results that AO is amorphous and STO is particularly crystalline structure can also be confirmed by HRTEM results. A core-shell nanostructure is found that crystalline structure is coated by amorphous layer (Fig. 3(d)). For crystalline core, the d space estimated from the lattice fringe is 0.275 nm (Fig. 3(e)), corresponding to the (110) planes of STO. No lattice fringes can be found in the shell, which means shell is an amorphous state. In order to prove the chemical component of the shell, the EDX analysis corresponding with HRTEM graphs is conducted. The spot scanning result (Fig. 3(f)) of the core-shell particle shows that particle is composed of STO and AO and line scanning from shell to core (Fig. 3(d)) proves that the shell is AO material. Amorphous AO and crystalline STO embrace great performance in breakdown strength and dielectric constant separately. Thus, it can be inferred that the core-shell structure composite film consisted by these two dielectric materials would have both excellent dielectric properties. Based on this, the electric properties of the composite film are deserved to study further. The dielectric breakdown strength (Eb) is a critical parameter to affect energy density of dielectric capacitors. Fig. 4(a) shows the fitted results of Weibull distribution for each sample’s breakdown strength. A two-parameter Weibull distribution function is applied: P(E) ¼ 1-exp(-(E/Eb)b), where P(E) is the cumulative probability of electric failure and its value is assigned on the basis of the position
Please cite this article as: W. Bi et al., Excellent energy density of crystalline SrTiO3@Amorphous Al2O3 nanocomposite combined with electrodeinduced interfacial reaction, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.153196
4
W. Bi et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
Fig. 2. Mapping EDX analysis of elements in first two composite slurry layers of film: (a1) STO_nps@AO; (b1) TEP-modified STO_nps@AO. SEM images corresponding with EDX results for first two composite slurry layers: (a2) STO_nps@AO; (b2) TEP-modified STO_nps@AO.
ith of an observation among the n ordered E-values as P ¼ i/(nþ1) [32,33], E is experimental breakdown strength, Eb is the characteristic breakdown strength, b is the Weibull modulus related to the linear regressive fit of the distribution. Except for the sample of (Al) STO_nps@AO, the b values for other three are more than 10 which guarantee a valid comparison of Eb. The TEP-modified ones show an improvement of Eb than those without TEP, as the Eb of (Au)TEPmodified STO_nps@AO is about 190% enhancement compared with (Au)STO_nps@AO. So, the following study mainly focused on TEPmodified sample. The TEP-modified STO_nps@AO with Au top electrode shows a proper breakdown strength of 118.4 MV/m. Moreover, with Al top electrode the Eb of modified samples is enormously strengthened to 341.8 MV/m, which is enhanced by 188%. Their current-electric field characteristics are presented in Fig. 4(b). The leakage current of (Au)TEP-modified STO_nps@AO increases with an increase in electric field and breaks down at ~118 MV/m. While the (Al)TEP-modified STO_nps@AO holds a current plateau before the damage (~340 MV/m) finally occurs. The dielectric constant is also studied to decide the energy density of the composite film. The dielectric constant and dielectric loss are measured at room temperature from 100 Hz to 1 MHz. At 100 kHz, the relative dielectric constant of TEP-modified STO_nps@AO is about 24. According to previous study, the relative dielectric constant of pure AO amorphous film is just 9 [34] and the one for crystalline STO can reach 300 [19]. So, owing to STO nanoparticle added, dielectric constant of the composite film can be boosted. Furthermore, the TEP-modified STO_nps@AO composite film shows a low dielectric loss about 0.05 at 100 kHz. As the breakdown strength and dielectric loss obtained, the energy density can be calculated. The energy density of the composite film with Au top electrode is 1.5 J/cm3. However, with Al as top electrode, the TEP-modified composite film obtains an enhanced energy storage of 12.2 J/cm3, which is rather impressive and deserves for further study. TEP-modified composite film with Al top electrode shows great
energy density. Considering practical application of this materials, the energy release properties of the (Al)TEP-modified STO_nps@AO are studied. The charge-discharge experiment is taken by being charged through a DC high voltage source and then directly shorted circuited without the load resistor. The sinusoidal discharge current-time curves under different electric field are displayed in Fig. 4(d), indicating the circuit is underdamped. The maximum of the current depends on the charge voltage. In present study, under electric field of 150 MV/m, the current amplitude reaches the maximum as the first current peak (Imax) is 0.45A. Adopting aluminum top electrode with a diameter of 1 mm, the maximum current density is 57.30 A/cm3, and the discharge period is about 13 ns according to the first half period. The whole discharge duration lasts about 250 ns, which shows a fast discharge performance for pulsed capacitors. Theoretically, the maximum power density can be approximately expressed as following: Pmax ¼ EImax/2S, where E, Imax and S are electric field, current amplitude and area of the electrode, respectively [35]. Under electric field of 150 MV/m, according to above expression, the maximum power density Pmax can be calculated to be 42.97 MW/cm3. Comparing with other material applied in pulse power system [35e37], (Al)TEP-modified STO_nps@AO can embrace a faster discharge speed and a remarkable power density, demonstrating the feasibility for application in energy storage system. 3.3. Analysis for distinct improvement of (Al)TEP-modified STO_nps@AO As described above, the TEP modified samples hold a high breakdown strength, especially the TEP-modified one with Al top electrode presents a far better electrical property. This kind of considerable improvement is conjectured to be relevant with electrode material that adopting aluminum as the top electrode would trigger a modification for the composite film. With Al as the top electrode, anodic oxidation reaction is the mechanism as the
Please cite this article as: W. Bi et al., Excellent energy density of crystalline SrTiO3@Amorphous Al2O3 nanocomposite combined with electrodeinduced interfacial reaction, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.153196
W. Bi et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
5
Fig. 3. XRD patterns: (a) pristine STO nanoparticles (b) composite slurry layers (c) the surface of composite film (TEP-modified STO_nps@AO). HRTEM patterns of TEP-modified STO_nps@AO powders: (d) (e) morphology (f) EDX point scanning (g) EDX line scanning.
reaction model exhibited in Fig. 5. Under the applied electric field, the O2- anions decomposed from structure water and absorbed water in the film move towards anode. At the same time, driven by high electrical field, the mobile Al3þ ions stemming from Al electrode combine with O2- anions to form AO. The AO generated from
anodic oxidation reaction is considered as part of barrier type which embraces excellent dielectric properties, as the breakdown strength for barrier type anodic AO film can achieve 700e1000 MV/ m [38]. The whole reaction process can be inferred having a positive change for film’s original structure, mainly reflected in two aspects:
Please cite this article as: W. Bi et al., Excellent energy density of crystalline SrTiO3@Amorphous Al2O3 nanocomposite combined with electrodeinduced interfacial reaction, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.153196
6
W. Bi et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
Fig. 4. (a) Weibull distribution of the dielectric breakdown strength for STO_nps@AO and TEP-modified STO_nps@AO with Au or Al top electrode (inset figure: broken line for breakdown strength of each sample and column diagram for Weibull modulus of each sample). (b) The I-E characteristics for TEP-modified STO_nps@AO with Au or Al top electrode. (c) The dielectric constant and dielectric loss of TEP-modified STO_nps@AO with Au or Al top electrode. (d) The discharge current waveforms of (Al)TEP-modified STO_nps@AO under different electric fields without load resistor.
Firstly, at the composite film surface (film-electrode interface), the new born AO fills the cracks and hole at the surface (Fig. 5(b)) and form a new dense AO layer at the interface between the top electrode and composite film which has capability to undertake higher electric field and decrease the breakdown probability. Secondly, the holes inside the composite film (Fig. 5(c)) could be filled up with new generated AO. According to electric field distribution in nonuniform dielectric, cracks and holes with air in them bring nonuniform of dielectric constant as the air’s dielectric constant is much lower than the composite film, which leads to local high electric field concentration in these defected areas. Overall, one effective interfacial modification based on anodic oxidation reaction is implemented with Al top electrode under high electric field. The process and actual effect are systematically studied as follows. To further confirm this modification of composite film under electric field, a sequence of tests has been carried out. As shown in Fig. 6(a), I-V measurement is applied 10 times for one (Al)TEPmodified STO_nps@AO sample where the positive voltage is arranged from 0 V to 250 V in successive steps of 0.5 V with a delay time of 0.1 s and after each IeV measurement the sample is shortcircuited to maintain the electrical equilibrium. For the first measurement, the leakage current shows a sharp rise to 1 106 A at the beginning, slowly increases to about 1 105 A, and then keeps relatively stable current plateau. At this plateau, with the linear increase of the applied electric field, the leakage current keeps unchanged. Thus, according to Ohm’s law, the resistance of the film
must increase in linear way with the electric field. The resistance improvement represents the modification of the composite film with newborn AO generated from anodic oxidation reaction. Besides, this modification process has been basically completed in the first-time IeV measurement, because no obvious leakage current plateau can be found in the later IeV measurements and the overall leakage current dramatically decreases about 2 magnitude. The growth of the resistance can also be confirmed in constant voltage and constant current curves as shown in Fig. 6(b). For the voltage set to be unchanged, the relationship between current and the resistance is inverse proportional in the basis of Ohm’s law. The current declines in the figure represents the improvement of resistance for composite film. When the current remains constant, there is a linear relationship between the voltage and the resistance. The resistance is speculated to be linear growth as the voltage shows a good linear curve. Based on the modification reaction model above, the increase of the resistance of the composite film is supposed to be generation of new interfacial AO layer and mending for defects. The IeV measurements for TEP-modified STO_nps@AO with different electrode thickness are prepared in Fig. 6(c). With Al top electrode about 65 nm, after remaining stable till ~200 MV/m the leakage current suddenly drops and then slightly grows until final breakdown occurs. The microscopic image of the sample after breakdown demonstrates the gray aluminum electrode is almost exhausted, where the circuit is cut off resulted in the drop of
Please cite this article as: W. Bi et al., Excellent energy density of crystalline SrTiO3@Amorphous Al2O3 nanocomposite combined with electrodeinduced interfacial reaction, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.153196
W. Bi et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
7
Fig. 5. (a) The anodic oxidation modification process model of composite film with Al electrode under high electric field. (b) Defects at the surface of TEP-modified STO_nps@AO sample without top electrode. (c) Defects in the interior TEP-modified STO_nps@AO sample without top electrode.
current in the graph. On the contrary, for Al top electrode thickness about 200 nm, the sudden drop of current at ~200 MV/m is erased. And a leakage current plateau can be detected which represents resistance improvement of composite film with new generated AO. When measurements finished, the Al electrode is intact except for the breakdown point at the spot of the test probe. Clearly, the top Al electrode takes part in the anodic oxidation reaction and the TEPmodified STO_nps@AO composite film with 200 nm Al top electrode embraces an excellent anodic oxidation capability. Fig. 6(d) shows the results of high-resolution XPS spectra analysis for Al 2p at electrode surface before and after IeV measurements. Before the tests, two peaks at 72.58 eV and 75.08 eV have been clearly found corresponding to metal state and oxide state of aluminum respectively, which shows the aluminum top electrode with a metallic oxide surface [24,39]. Yet after breakdown, the two peaks are replaced by one, which is at 74.11 eV corresponding to Al 2p of a new aluminum oxide [40]. The disappear of peak Al 2p from metal aluminum and the shift of the binding energy of Al 2p suggest that the top electrode takes part in the anodic oxidation modification process and a new AO is generated from this reaction. The above electrical measurements along with chemical analysis can be used as reasonable experimental evidences to testify that the newborn AO was created from anodic oxidation modification process. The FESEM cross section images of the sample before and after IeV measurements provides direct evidence for interfacial modification (Fig. 7). After IeV measurement, a dense
interface layer generated between the composite film and the Al top electrode can be seen with the consumption of Al electrode. Given the result of previous analysis and relevant studies, the newly interfacial layer is ascribed to be aluminum oxide from anodic oxidation reaction, whose resistivity and breakdown strength are ultra-high [41,42]. Moreover, the thickness of this new generated layer is proved to be reasonable according to that the thickness ratio of the oxide film to the aluminum layer replaced is about 0.725 [43]. According to above experimental analysis added with microstructure analysis, the interface modification model can be verified. Anodic oxidation is the major reaction mechanism where the newborn interfacial AO layer is the main characteristics. To further learn about the dielectric characteristics of the newborn anodic oxidation layer, impedance analysis methods are applied for this composite film with Al top electrode. IeV measurements from 0 V to 250 V are taken to produce the anodic oxidation layer while maintain the whole film intact. The Nyquist plots of (Al)TEP-modified STO_nps@AO sample before and after IeV measurement are shown separately in Fig. 8(a) and (b) with corresponding equivalent circuit mode and the fitting results. For Nyquist curves, the similar capacitive semicircle (Semicircle A) can be found in both before and after IeV measurement, which is correspond to composite film. However, after the measurement, data from lower frequency trends to form another capacitive semicircle (Semicircle B) which is regarded from the newly generated AO layer. According to the geometrical parameters of
Please cite this article as: W. Bi et al., Excellent energy density of crystalline SrTiO3@Amorphous Al2O3 nanocomposite combined with electrodeinduced interfacial reaction, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.153196
8
W. Bi et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
Fig. 6. (a) The I-E characteristics of repeating IeV measurements for the same (Al)TEP-modified STO_nps@AO sample. (b)Constant current (10 mA cm2) and constant voltage (40 V) for (Al)TEP-modified STO_nps@AO sample. (c) The IeV measurements of TEP-modified STO_nps@AO sample with Al top electrode of different thickness and the images for Al top electrode when the measurement finished. (d) High resolution XPS spectra of Al 2p peaks for composite film with Al top electrode before and after IeV measurements.
composite film and the newborn AO layer, the corresponding dielectric constant and resistivity can be calculated as shown in the tables, which basically conforms to testing data. The Bode plot is provided in Fig. 8(c). A plateau generated with a phase angle close to 90 explains the present system is close to a nearly ideal capacitor [44]. Similarly, plateau A correlated with capacitor system of composite film exists before and after IeV measurement. Base on the results of Nyquist plot, plateau B should arise at lower frequency, which shows capacitor behavior of newly generated anodic oxidation layer. The model based on above impedance analysis is
shown in Fig. 8(d). Before IeV measurement, the sample just include one capacitor system of composite film showing a highfrequency capacitor behavior. With application of electric field, newborn AO layer at the electrode-film interface provides a new capacitor system in low-frequency region. In all, applying Al as the top electrode, the new AO layer generated from anodic oxidation shows an ideal capacitor behavior with high resistance, which contributes greatly to improve the dielectric breakdown strength and showing an excellent interface modification effect.
Fig. 7. SEM cross-sectional micrographs of TEP-modified STO_nps@AO sample before and after IeV measurement.
Please cite this article as: W. Bi et al., Excellent energy density of crystalline SrTiO3@Amorphous Al2O3 nanocomposite combined with electrodeinduced interfacial reaction, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.153196
W. Bi et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
9
Fig. 8. Nyquist (impedance) plot with equivalent circuit mode and fitting results (a) (b), Bode plot (c) and model of impedance analysis (d) for the TEP-modified STO_nps@AO sample with Al top electrode before and after IeV measurement.
4. Conclusion In summary, composite dielectric film combining STO crystalline nanoparticles and amorphous AO is fabricated by spin coating process. With TEP added as a dispersing agent, the homogeneity and compatibility of the composite film have been effectively promoted, leading to more compact structure with less defects. After TEP modified, the composite structure embraces a good performance in dielectric constant and breakdown strength. However, adopting aluminum as the top electrode, a superior energy density of 12.2 J/cm3 with breakdown strength about 340 MV/m can be achieved. A fast discharge speed and a remarkable power density confirmed its availability in pulse energy storage device. The improvement of the composite film with Al top electrode is attributed to that the Al electrode can activate anodic oxidation under electric field which causes interface modification. An anodic oxidation interface modification model is provided based on varied measurements and a distinct newborn AO found in microstructure profile which exhibits excellent capacitive performances. Our
finding will provide an inspiring idea to design dielectric composite film assimilating the high breakdown strength of amorphous dielectrics and excellent dielectric constant of crystalline dielectrics. Besides, the remarkable anodic oxidation interface modification based on top electrode material can be applied in the composite film, which could promote the advanced development in energy storage materials and devices.
Author contribution statement Wei Bi: Methodology, Investigation, Validation, Formal analysis, WritingdOriginal draft. Manwen Yao: Conceptualization, Supervision, Project administration, Funding acquisition. Wenbin Gao: formal analysis, Resources, Writing-Review and Editing. Zhen Su: Formal analysis, Writing-Review and Editing. Xi Yao: Conceptualization, Project administration.
Please cite this article as: W. Bi et al., Excellent energy density of crystalline SrTiO3@Amorphous Al2O3 nanocomposite combined with electrodeinduced interfacial reaction, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.153196
10
W. Bi et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
[19]
[20] [21]
Acknowledgments [22]
This work is supported by the Joint Fund of the Ministry of Education of China under the grant number 6141A02022433. References [1] G.P. Awasthi, D. Kumar, B.K. Shrestha, J. Kim, K.S. Kim, H.P. Chan, C.S. Kim, Layer e structured partially reduced graphene oxide sheathed mesoporous MoS 2 particles for energy storage applications, J. Colloid Interface Sci. 518 (2018) 234. [2] M.S. Javed, C. Jie, C. Lin, X. Yi, C. Hu, Flexible full-solid state supercapacitor based on zinc sulfide spheres growing on carbon textile with superior charge storage, J. Mater. Chem. 4 (2015) 667e674. [3] Q. Wei, F. Xiong, S. Tan, L. Huang, E.H. Lan, B. Dunn, L. Mai, Porous onedimensional nanomaterials: design, fabrication and applications in electrochemical energy storage, Adv. Mater. 29 (2017) 1602300. [4] H.O.M.Y., P.S. Khiew, D. Isa, T.K. Tan, W.S. Chiu, C.H. Chia, A review of metal oxide composite electrode materials for electrochemical capacitors, Nano 9 (2014). -. [5] Z. Xie, B. Peng, S. Meng, Y. Zhou, Z. Yue, S.E. Trolier-Mckinstry, Z. Xie, B. Peng, S. Meng, Y. Zhou, Higheenergy-storage density capacitors of Bi(Ni1/2Ti1/2) O3ePbTiO3 thin films with good temperature stability, J. Am. Ceram. Soc. 96 (2013) 2061e2064. [6] W. Gao, M. Yao, Y. Xi, Substantially improved energy density of SrTiO3 thin film by cyclic cooling-heating and interfacial blocking effect, J. Mater. Chem. C 6 (2018), https://doi.org/10.1039/c8tc01748d. [7] B. Peng, Z. Xie, Z. Yue, L. Li, Improvement of the recoverable energy storage density and efficiency by utilizing the linear dielectric response in ferroelectric capacitors, Appl. Phys. Lett. 105 (2014), 242909-242224. [8] Z.M. Dang, J.K. Yuan, S.H. Yao, R.J. Liao, Flexible nanodielectric materials with high permittivity for power energy storage, ChemInform 25 (2013) 6334e6365. [9] J.Y. Li, L. Zhang, S. Ducharme, Electric energy density of dielectric nanocomposites, Appl. Phys. Lett. 90 (2007) 132901. [10] J.W. McPherson, K. Jinyoung, A. Shanware, H. Mogul, J. Rodriguez, Trends in the ultimate breakdown strength of high dielectric-constant materials, IEEE Trans. Electron Devices 50 (2003) 1771e1778. [11] L. Yao, Z. Pan, S. Liu, J. Zhai, H.H. Chen, Significantly enhanced energy density in nanocomposite capacitors combining the TiO2 nanorod array with poly(vinylidene fluoride), ACS Appl. Mater. Interfaces 8 (2016) 26343. [12] Z. Pan, L. Yao, J. Zhai, S. Bo, H. Wang, Significantly improved dielectric properties and energy density of polymer nanocomposites via small loaded of BaTiO 3 nanotubes, Compos. Sci. Technol. 147 (2017). S0266353817304049. [13] H. Tang, H.A. Sodano, Ultra high energy density nanocomposite capacitors with fast discharge using Ba0.2Sr0.8TiO3 nanowires, Nano Lett. 13 (2013) 1373e1379. [14] L. Yao, Z. Pan, J. Zhai, G. Zhang, Z. Liu, Y. Liu, High-energy-density with polymer nanocomposites containing of SrTiO3 nanofibers for capacitor application, Compos. Part A-Appl. S. 109 (2018) 48e54. [15] T. Haixiong, L. Yirong, A. Clark, H.A. Sodano, Nanocomposites with increased energy density through high aspect ratio PZT nanowires, Nanotechnology 22 (2011), 015702. [16] L. Fei, M. Yao, S. Zhen, J. Chen, P. Yong, Q. Li, Y. Xi, Enhancement of breakdown strength of SrTiO 3/nano-SiO 2 composite film prepared by sol-gel technology, Ceram. Int. 43 (2016). [17] X. Zhang, J. Jiang, Z. Shen, Z. Dan, M. Li, Y. Lin, C.W. Nan, L. Chen, Y. Shen, Polymer nanocomposites with ultrahigh energy density and high discharge efficiency by modulating their nanostructures in three dimensions, Adv. Mater. 30 (2018). [18] Z. Pan, L. Yao, J.W. Zhai, Y. Ke, S. Bo, H. Wang, Ultrafast discharge and highenergy-density of polymer nanocomposites achieved via optimizing the
[23]
[24]
[25] [26]
[27] [28]
[29] [30]
[31] [32] [33] [34]
[35]
[36]
[37]
[38]
[39]
[40] [41] [42] [43]
[44]
structure design of barium titanates, ACS Sustain. Chem. Eng. 5 (2017) acssuschemeng.7b00080. R. Thomas, D.C. Dube, M.N. Kamalasanan, S. Chandra, A.S. Bhalla, Structural, electrical, and low-temperature dielectric properties of solegel derived SrTiO3 thin films, J. Appl. Phys. 82 (1997) 4484e4488. H.H. Barrett, Dielectric breakdown of single-crystal strontium titanate, J. Appl. Phys. 35 (1964) 1420e1425. I. Burn, D.M. Smyth, Energy storage in ceramic dielectrics, J. Mater. Sci. 7 (1972) 339e343. P. Yong, M. Yao, J. Chen, K. Xu, Y. Xi, Electrical characteristics of SrTiO3/Al2O3 laminated film capacitors, J. Appl. Phys. 120 (2016), 08NA02. M. Yao, P. Yong, R. Xiao, Q. Li, Y. Xi, Enhanced self-repairing capability of solgel derived SrTiO3/nano Al2O3 composite films, Appl. Phys. Lett. 109 (2016) 202901. K.C. Chiang, C.H. Cheng, H.C. Pan, C.N. Hsiao, C.P. Chou, A. Chin, H.L. Hwang, High-temperature leakage improvement in metaleinsulatoremetal capacitors by workefunction tuning, IEEE Electron. Device Lett. 28 (2007) 235e237. Y. Matsumoto, Y. Matsumoto, Solid oxide electrochemical doping (SOED) method, Solid State Ion. 100 (1997) 165e168. J.P. Manceau, S. Bruyere, S. Jeannot, A. Sylvestre, P. Gonon, Metal-insulatormetal capacitors’ current instability improvement using dielectric stacks to prevent oxygen vacancies formation, Appl. Phys. Lett. 91 (2007) 2e262. G. Yip, J. Qiu, W.T. Ng, Z.H. Lu, Effect of metal contacts on the electrical characteristics of Al2O3 dielectric thin films, Appl. Phys. Lett. 92 (2008) 99. S. Zhen, M. Yao, L. Fei, P. Yong, F. Qian, Y. Xi, Microstructural transitions and dielectric properties of boron-doped amorphous alumina thin film, J. Mater. Sci. 52 (2017) 9314e9323. R.E. Mistler, E.R. Twiname, Surfactant Tape casting: theory and practice, Am. Ceram. Soc. (2015). S. Ogitani, S.A. Bidstrup-Allen, P.A. Kohl, Factors influencing the permittivity of polymer/ceramic composites for embedded capacitors, IEEE Trans. Adv. Packag. 23 (2000) 313e322. K.R. Mikeska, W.R. Cannon, Non-aqueous dispersion properties of pure barium titanate for tape casting, Colloids Surface. 29 (1988) 305e321. ndez-Sa ez, C. Navarro, On the estimation of percentiles of E. Barbero, J. Ferna the Weibull distribution, J. Mater. Sci. Lett. 18 (1999) 1441e1443. E. Barbero, J. Fern andez-S aez, C. Navarro, Statistical analysis of the mechanical properties of composite materials, Compos. B Eng. 31 (5) (2000) 375e381. L. Mengxin, Y. Manwen, S. Zhen, G. Wenbin, Y. Xi, Improved breakdown strength and energy density of Al2O3/nano-ZrO2 composite films via enhanced interfacial repairing behavior, Ceram. Int. (2018). S0272884218322788. C. Xu, L. Zhen, X. Chen, S. Yan, G. Wang, High charge-discharge performance of Pb0.98La0.02(Zr0.35Sn0.55Ti0.10)0.995O3 antiferroelectric ceramics, J. Appl. Phys. 120 (2016) 324. X. Ran, X. Zhuo, Y. Feng, X. Wei, J. Tian, Nonlinear dielectric and discharge properties of Pb0.94La0.04[(Zr0.56Sn0.44)0.84Ti0.16]O3 antiferroelectric ceramics, J. Appl. Phys. 120 (2016) 332. C. Pan, S. Wu, P. Li, J. Zhai, S. Bo, Great enhancement of energy storage density and power density in BNBT/BFO multilayer thin film hetero-structures, Inorg. Chem. Front. 5 (2018), 10.1039.C1038QI00487K. M. Yao, J. Chen, Z. Su, Y. Peng, P. Zou, X. Yao, Anodic oxidation in aluminum electrode by using hydrated amorphous aluminum oxide film as solid electrolyte under high electric field, ACS Appl. Mater. Interfaces 8 (2016) 11100e11107. Y.-C. Kim, H.-H. Park, J.S. Chun, W.-J. Lee, Compositional and structural analysis of aluminum oxide films prepared by plasma-enhanced chemical vapor deposition, Thin Solid Films 237 (1994) 57e65. H. He, K. Alberti, T.L. Barr, J. Klinowski, ESCA studies of aluminophosphate molecular sieves, J. Phys. Chem. 97 (1993) 13703e13707. H.J.D. Wit, C. Crevecoeur, The dielectric breakdown of anodic aluminum oxide, Phys. Lett. A 50 (1974) 365e366. J.R. Dickey, Improved dielectric properties for anodic aluminum oxide films by soft/hard two-step electrolytic anodization, ChemInform (1989) 20. J. Chen, M. Yao, R. Xiao, P. Yang, B. Hu, X. Yao, The application of the barriertype anodic oxidation method to thickness testing of aluminum films, Rev. Sci. Instrum. 85 (2014) 313e315. H. Berney, J. West, E. Haefele, J. Alderman, W. Lane, J.K. Collins, Chemical: a dna diagnostic biosensor: development, characterisation and performance, Sens. Actuator 68 (2000) 100e108.
Please cite this article as: W. Bi et al., Excellent energy density of crystalline SrTiO3@Amorphous Al2O3 nanocomposite combined with electrodeinduced interfacial reaction, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.153196
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Excellent energy density of crystalline SrTiO3@Amorphous Al2O3 nanocomposite combined with electrode-induced interfacial reaction Wei Bi a, Manwen Yao a, *, Wenbin Gao b, Zhen Su a, Xi Yao a a
Functional Materials Research Laboratory, School of Materials Science and Engineering, Tongji University, Shanghai, 200092, China Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education & International Center for Dielectric Research, Xi’an Jiaotong University, Xi’an, 710049, China b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 4 August 2019 Received in revised form 25 November 2019 Accepted 26 November 2019 Available online xxx
Simultaneously enhancing the breakdown strength and the dielectric constant is considered as a trend in material design for increasing energy density of linear dielectrics. Based on this point, crystalline SrTiO3 nanoparticle@amorphous Al2O3 composite film (Au top electrode) is prepared via spin coating process with dielectric strength of 118.1 MV/m and dielectric constant of 23.6. Further, under aluminum top electrode, higher breakdown strength of 342.9 MV/m and superior energy density of 12.2 J/cm3 are realized, which is stemmed from anodic oxidation reaction at the interface between the aluminum electrode and the composite dielectric film. This new composite structure shows an improved energy density, which provides a feasible avenue to design excellent inorganic dielectric composites assimilating the high breakdown strength of amorphous structure and high dielectric constant of crystalline dielectrics. © 2019 Elsevier B.V. All rights reserved.
Keywords: Composite dielectric film Dielectric constant Breakdown strength Energy density Interface modification Anodic oxidation
1. Introduction Developing energy storage technologies is one of the most promising options to solve the serious energy shortage problem in 21st century and meet the ever-increasing energy requirements [1e3]. Among various available electrical energy storage devices, dielectric capacitor plays a vital role in high-power density applications owing to its ultrafast charging-discharging rate and high operating voltage [4e6]. But there is still a challenge for improving its energy density. The energy density (U) of dielectric capacitor is determined by the applied field (E) and the electric displacement (D), given by U ¼ !EdD. For liner dielectrics, it can be defined as following: U ¼ 1/ 2DEb ¼ 1/2ε0εrE2b, where ε0 is the vacuum dielectric permittivity (8.854 1012 F/m), εr is the relative dielectric constant and Eb is dielectric strength [7]. Therefore, a high dielectric strength and a large dielectric constant are required. However, traditional dielectric materials are ceramics with large dielectric constant but small breakdown strength. New developed polymer dielectric materials embrace relatively high electric breakdown field but short of
* Corresponding author. E-mail address: [email protected] (M. Yao).
dielectric constant value [8,9]. Researchers widely studied many types of materials and provided one relationship based on theory and experiment: Eb ~ ε-½ [10], which means a limitation for achieving high breakdown strength and giant dielectric constant simultaneously in one material. Hence, tremendous efforts have been made towards material recombination, micro-structure design, and process innovation in order to achieve optimal relationship between two key parameters and explore new dielectric materials with great energy density. For example, (a) introducing inorganic material of large dielectric constant, as TiO2, BaTiO3, SrTiO3, Pb (Zr, Ti) O3 etc., into polymer dielectric matrix with high breakdown strength [11e15] and adding nano particles into amorphous dielectric film to improve its properties based on nano effect [16]; (b) controlling the 3D distribution and orientation of oxide nanoparticles in a polymer matrix to resolve the paradox between dielectric constant and breakdown strength [17] and changing the nanostructure of additions to accomplish complication of breakdown path then to increase final breakdown strength [18]; (c) with requirement of complex design for dielectric material, applying different methods such electrospinning, tape-casting, traditional ceramic techniques and so on combined with dispersants or surfactants to investigate promising dielectrics [12]. Clearly, composites, microstructure design and technical
https://doi.org/10.1016/j.jallcom.2019.153196 0925-8388/© 2019 Elsevier B.V. All rights reserved.
Please cite this article as: W. Bi et al., Excellent energy density of crystalline SrTiO3@Amorphous Al2O3 nanocomposite combined with electrodeinduced interfacial reaction, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.153196
2
W. Bi et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
improvement are research trends for exploring high energy density dielectrics with the breakdown strength and dielectric constant improved simultaneously. With great properties, linear dielectric capacitor is one most effective device for energy storage whose dielectric constant is independent of electric field. Aluminum oxide (Al2O3, abbreviated as AO) and strontium titanite (SrTiO3, abbreviated as STO) have been widely studied as representative of linear dielectrics. AO is a promising material for high energy density storage capacitors due to its high breakdown strength(300e700 MV/m),high band gap(~9 eV) and its chemical and thermal stabilities. However, comparing to other dielectric material, its dielectric constant (8.6e10) would be the limitation for improvement in energy density storage. STO with crystalline structure embraces a relatively high dielectric constant around 300, which is much higher than AO [19]. However, it is reported that mean dielectric strength of a STO single crystal is just 40 MV/m [20,21]. Thus, merging these two’s great properties provides a design idea for inorganic composite dielectrics, which holds a thermal endurance compared with organic dielectric composites. Several researches have been tried referring to this idea, such as SrTiO3/Al2O3 laminated film capacitors and nano-Al2O3 particles doped SrTiO3 composite films, exhibiting a great progress in dielectric strength [22,23]. In this work, a composite is designed combining large dielectric constant of STO crystalline nanoparticles and high breakdown strength of amorphous AO to accomplish development for energy density. The electrode materials would influence the electrical characteristics, which is another hotspot aimed to optimize dielectric capacitors [24e26]. For example, Yip et al. prepared thick Al2O3 insulator with Al electrode and found the leakage current and breakdown strength are strongly improved because of one likely mechanism based on ionization potential and diffusion coefficient [27]. To learn the effect of different electrodes on dielectric material, two kinds of top electrode, gold and aluminum, are adopted on this composite dielectric. In this study, complementary advantages of crystal SrTiO3 and amorphous Al2O3 have been merged to gain a superimposed effect, leading to a proper enhancement in both dielectric constant and breakdown strength. In order to achieve this composite film with structural integrity, ball milling blending process is applied combining with triethyl phosphate (TEP) as one effective dispersing agent. As the electrode material can help optimize the dielectric behaviors of the film, two kinds of top electrode are adopted. Under the Au top electrode, the composite dielectric film shows a good dielectric performance with dielectric strength of 118.1 MV/m and dielectric constant of 23.6. Compared to Au top electrodes, this composite film with Al top electrode exhibited great improvement in the dielectric strength to 342.9 MV/m, result in the energy density reaching 12.2 J/cm3. To better understand this improvement, one mechanism based on anodic oxidation reaction is proposed with relevant experimental evidences. A newborn AO layer with excellent dielectric strength is generated at the electrode-film interface to realize an interface modification for the composite film, which is the reason that the composite film with Al top electrode can embrace great dielectric properties. This work provides a new approach for designing high energy-density inorganic dielectric composites. 2. Experimental 2.1. Preparation A notable stable 0.04 M alumina sol was prepared by conventional sol-gel process. The details for the sol-gel process can be found in Ref. [28]. Then commercial STO powders (a mean particle
size of 151 nm) were added into the alumina sol. Moreover, a small amount of triethyl phosphate (TEP), as an organic dispersant, was added into the above solution to disperse STO nanoparticles in AO sol [29]. Wet-ball-mixing was applied for 24 h. Then the mixture was stirred for 3 h to form a stable composite slurry. Spin-coating was used to deposit the composite slurry or pure 0.04 M alumina sol onto the Pt/Ti/SiO2/Si substrate at 3000 rpm for 30 s. Here, we prepared 5-layer composite dielectric film. The first two layers were the composite slurry layers. Then 3-layer pure 0.04 M alumina sol was deposited on them, which was attempted to improve the roughness of the surface of the composite film to benefit for coating electrode further. Each layer was conducted with pre-heating process to remove the organics. When the deposition was finished, the films were annealed at 450 C for 3 h to obtain the final nanocomposite dielectric film. Then Al or Au top electrode with diameter of 1 mm was fabricated by ion sputtering for further measurements. In following discussion, for composite slurry with/ without organic dispersant (TEP), the samples were abbreviated as TEP-modified STO_nps@AO/STO_nps@AO. Fig. 1(a) is the process illustration for samples of nanocomposite dielectric film. Fig. 1(b) exhibits the structure of composite film by the SEM cross profile of (Al)TEP-modified STO_nps@AO as the representation. The total thickness for samples is about 1.5 mm. 2.2. Characterization The phase structure of nanoparticles and nanocomposite film was investigated by the X-ray diffraction (XRD, Rigaku D/max2550, Rigaku, Japan) patterns with an incident angle of 1. The microstructure of the composite and relative EDX analysis were learned using a high-resolution transmission electron microscope (HRTEM) (JEM-2011F). The microstructure morphology characterization and relative EDX analysis were measured with field emission scanning electron microscopy (FESEM, Philips XL30). Relevant electric tests, as current-electric field measurement, were performed by a computer-controlled voltage/current source (2400, Keithley, USA). Impedance spectroscopy to learn dielectric properties were carried out by precision impedance analyzer (Agilent 4294A). The discharge properties are studied through the chargedischarge platform (CFD-001) supplied by Gogo Instruments Technology Co. Ltd. 3. Results and discussion 3.1. The improvement of composite film structure with organic dispersant TEP To achieve a good microstructure of the composite film, organic dispersant TEP is used here to adjust the compatibility and dispersibility of the first two composite slurry layers. To learn about the TEP-modified effect on the elements’ distribution, mapping EDAX analysis of composite slurry layers’ surface is performed. According to the analysis (Fig. 2 (a1) and (b1)), STO nanoparticles can be more uniform distributed in aluminum sol in TEP-modified STO_nps@AO samples, reflected in a more even distribution of elements. The surface SEM pictures exhibit the micro-structure of the composite slurry layers. For samples without TEP, the alumina sol separating the STO particles turns into lots of nano-sized small alumina grains adhering around larger STO particles as shown in the close-up view in Fig. 2 (a2). On the contrast, STO particles can be firmly encapsulated by alumina sol after TEP modified, forming a compact and uniform surface structure as shown in Fig. 2(b2). The TEP can effectively improve the compatibility between STO powders and AO to achieve the composite slurry layers’ uniformity. TEP is one simple chemical structure phosphate ester surfactant
Please cite this article as: W. Bi et al., Excellent energy density of crystalline SrTiO3@Amorphous Al2O3 nanocomposite combined with electrodeinduced interfacial reaction, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.153196
W. Bi et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
3
Fig. 1. (a) Process illustration for samples of nanocomposite dielectric film. (b) Composite film structure exhibited by the SEM cross profile of (Al)TEP-modified STO_nps@AO.
effectively used in our research. Phosphate ester surfactant as a dispersant is widely used in traditional ceramic process [30]. K.R. Mikeska et al. detailed mechanism by which the phosphate ester disperses the barium titanite particles [31], which provides an idea to understand the dispersion effect of TEP for our research. The heating effect of high-speed ball-milling and the acid condition of the AO sol make TEP hydrolyze into diethyl phosphate, which would easily ionize to be an anionic surfactant. The anionic surfactant absorbed on the ceramic particle plays a wetting role, improving the compatibility. Besides, the structure of phosphate ester suggests a steric contribution and the dissociation of the diethyl phosphate contributes a diffuse layer of ions adjacent to the solid surface forming static hindrance, reducing the agglomeration of nanoparticles. In general, with TEP modification, the compatibility of two material and the dispersity of STO nanoparticle in AO sol are effectively improved, which lays a root for further study of this composite materials’ structure and performance. 3.2. Nanostructure and electrical properties of composite films Start with the materials’ structure, it can be clear to understand their characteristics. The XRD patterns of pristine STO nanoparticles, composite slurry layers, and composite film are displayed in Fig. 3((a) (b) (c)). Pristine STO are crystalline nanoparticles as perovskite structure of STO can be clearly found according to the standard PDF card (No. 73e0661) (Fig. 3(a)). For composite slurry layers (Fig. 3(b)), perovskite structure of STO is also distinct and no
AO peak could be found. Besides, in composite film of Fig. 3(c), for the samples’ surface is pure alumina layers, characteristic peaks of STO is attenuated but still no peaks for AO. It can be speculated that the AO are amorphous phase in composite film. The XRD results that AO is amorphous and STO is particularly crystalline structure can also be confirmed by HRTEM results. A core-shell nanostructure is found that crystalline structure is coated by amorphous layer (Fig. 3(d)). For crystalline core, the d space estimated from the lattice fringe is 0.275 nm (Fig. 3(e)), corresponding to the (110) planes of STO. No lattice fringes can be found in the shell, which means shell is an amorphous state. In order to prove the chemical component of the shell, the EDX analysis corresponding with HRTEM graphs is conducted. The spot scanning result (Fig. 3(f)) of the core-shell particle shows that particle is composed of STO and AO and line scanning from shell to core (Fig. 3(d)) proves that the shell is AO material. Amorphous AO and crystalline STO embrace great performance in breakdown strength and dielectric constant separately. Thus, it can be inferred that the core-shell structure composite film consisted by these two dielectric materials would have both excellent dielectric properties. Based on this, the electric properties of the composite film are deserved to study further. The dielectric breakdown strength (Eb) is a critical parameter to affect energy density of dielectric capacitors. Fig. 4(a) shows the fitted results of Weibull distribution for each sample’s breakdown strength. A two-parameter Weibull distribution function is applied: P(E) ¼ 1-exp(-(E/Eb)b), where P(E) is the cumulative probability of electric failure and its value is assigned on the basis of the position
Please cite this article as: W. Bi et al., Excellent energy density of crystalline SrTiO3@Amorphous Al2O3 nanocomposite combined with electrodeinduced interfacial reaction, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.153196
4
W. Bi et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
Fig. 2. Mapping EDX analysis of elements in first two composite slurry layers of film: (a1) STO_nps@AO; (b1) TEP-modified STO_nps@AO. SEM images corresponding with EDX results for first two composite slurry layers: (a2) STO_nps@AO; (b2) TEP-modified STO_nps@AO.
ith of an observation among the n ordered E-values as P ¼ i/(nþ1) [32,33], E is experimental breakdown strength, Eb is the characteristic breakdown strength, b is the Weibull modulus related to the linear regressive fit of the distribution. Except for the sample of (Al) STO_nps@AO, the b values for other three are more than 10 which guarantee a valid comparison of Eb. The TEP-modified ones show an improvement of Eb than those without TEP, as the Eb of (Au)TEPmodified STO_nps@AO is about 190% enhancement compared with (Au)STO_nps@AO. So, the following study mainly focused on TEPmodified sample. The TEP-modified STO_nps@AO with Au top electrode shows a proper breakdown strength of 118.4 MV/m. Moreover, with Al top electrode the Eb of modified samples is enormously strengthened to 341.8 MV/m, which is enhanced by 188%. Their current-electric field characteristics are presented in Fig. 4(b). The leakage current of (Au)TEP-modified STO_nps@AO increases with an increase in electric field and breaks down at ~118 MV/m. While the (Al)TEP-modified STO_nps@AO holds a current plateau before the damage (~340 MV/m) finally occurs. The dielectric constant is also studied to decide the energy density of the composite film. The dielectric constant and dielectric loss are measured at room temperature from 100 Hz to 1 MHz. At 100 kHz, the relative dielectric constant of TEP-modified STO_nps@AO is about 24. According to previous study, the relative dielectric constant of pure AO amorphous film is just 9 [34] and the one for crystalline STO can reach 300 [19]. So, owing to STO nanoparticle added, dielectric constant of the composite film can be boosted. Furthermore, the TEP-modified STO_nps@AO composite film shows a low dielectric loss about 0.05 at 100 kHz. As the breakdown strength and dielectric loss obtained, the energy density can be calculated. The energy density of the composite film with Au top electrode is 1.5 J/cm3. However, with Al as top electrode, the TEP-modified composite film obtains an enhanced energy storage of 12.2 J/cm3, which is rather impressive and deserves for further study. TEP-modified composite film with Al top electrode shows great
energy density. Considering practical application of this materials, the energy release properties of the (Al)TEP-modified STO_nps@AO are studied. The charge-discharge experiment is taken by being charged through a DC high voltage source and then directly shorted circuited without the load resistor. The sinusoidal discharge current-time curves under different electric field are displayed in Fig. 4(d), indicating the circuit is underdamped. The maximum of the current depends on the charge voltage. In present study, under electric field of 150 MV/m, the current amplitude reaches the maximum as the first current peak (Imax) is 0.45A. Adopting aluminum top electrode with a diameter of 1 mm, the maximum current density is 57.30 A/cm3, and the discharge period is about 13 ns according to the first half period. The whole discharge duration lasts about 250 ns, which shows a fast discharge performance for pulsed capacitors. Theoretically, the maximum power density can be approximately expressed as following: Pmax ¼ EImax/2S, where E, Imax and S are electric field, current amplitude and area of the electrode, respectively [35]. Under electric field of 150 MV/m, according to above expression, the maximum power density Pmax can be calculated to be 42.97 MW/cm3. Comparing with other material applied in pulse power system [35e37], (Al)TEP-modified STO_nps@AO can embrace a faster discharge speed and a remarkable power density, demonstrating the feasibility for application in energy storage system. 3.3. Analysis for distinct improvement of (Al)TEP-modified STO_nps@AO As described above, the TEP modified samples hold a high breakdown strength, especially the TEP-modified one with Al top electrode presents a far better electrical property. This kind of considerable improvement is conjectured to be relevant with electrode material that adopting aluminum as the top electrode would trigger a modification for the composite film. With Al as the top electrode, anodic oxidation reaction is the mechanism as the
Please cite this article as: W. Bi et al., Excellent energy density of crystalline SrTiO3@Amorphous Al2O3 nanocomposite combined with electrodeinduced interfacial reaction, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.153196
W. Bi et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
5
Fig. 3. XRD patterns: (a) pristine STO nanoparticles (b) composite slurry layers (c) the surface of composite film (TEP-modified STO_nps@AO). HRTEM patterns of TEP-modified STO_nps@AO powders: (d) (e) morphology (f) EDX point scanning (g) EDX line scanning.
reaction model exhibited in Fig. 5. Under the applied electric field, the O2- anions decomposed from structure water and absorbed water in the film move towards anode. At the same time, driven by high electrical field, the mobile Al3þ ions stemming from Al electrode combine with O2- anions to form AO. The AO generated from
anodic oxidation reaction is considered as part of barrier type which embraces excellent dielectric properties, as the breakdown strength for barrier type anodic AO film can achieve 700e1000 MV/ m [38]. The whole reaction process can be inferred having a positive change for film’s original structure, mainly reflected in two aspects:
Please cite this article as: W. Bi et al., Excellent energy density of crystalline SrTiO3@Amorphous Al2O3 nanocomposite combined with electrodeinduced interfacial reaction, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.153196
6
W. Bi et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
Fig. 4. (a) Weibull distribution of the dielectric breakdown strength for STO_nps@AO and TEP-modified STO_nps@AO with Au or Al top electrode (inset figure: broken line for breakdown strength of each sample and column diagram for Weibull modulus of each sample). (b) The I-E characteristics for TEP-modified STO_nps@AO with Au or Al top electrode. (c) The dielectric constant and dielectric loss of TEP-modified STO_nps@AO with Au or Al top electrode. (d) The discharge current waveforms of (Al)TEP-modified STO_nps@AO under different electric fields without load resistor.
Firstly, at the composite film surface (film-electrode interface), the new born AO fills the cracks and hole at the surface (Fig. 5(b)) and form a new dense AO layer at the interface between the top electrode and composite film which has capability to undertake higher electric field and decrease the breakdown probability. Secondly, the holes inside the composite film (Fig. 5(c)) could be filled up with new generated AO. According to electric field distribution in nonuniform dielectric, cracks and holes with air in them bring nonuniform of dielectric constant as the air’s dielectric constant is much lower than the composite film, which leads to local high electric field concentration in these defected areas. Overall, one effective interfacial modification based on anodic oxidation reaction is implemented with Al top electrode under high electric field. The process and actual effect are systematically studied as follows. To further confirm this modification of composite film under electric field, a sequence of tests has been carried out. As shown in Fig. 6(a), I-V measurement is applied 10 times for one (Al)TEPmodified STO_nps@AO sample where the positive voltage is arranged from 0 V to 250 V in successive steps of 0.5 V with a delay time of 0.1 s and after each IeV measurement the sample is shortcircuited to maintain the electrical equilibrium. For the first measurement, the leakage current shows a sharp rise to 1 106 A at the beginning, slowly increases to about 1 105 A, and then keeps relatively stable current plateau. At this plateau, with the linear increase of the applied electric field, the leakage current keeps unchanged. Thus, according to Ohm’s law, the resistance of the film
must increase in linear way with the electric field. The resistance improvement represents the modification of the composite film with newborn AO generated from anodic oxidation reaction. Besides, this modification process has been basically completed in the first-time IeV measurement, because no obvious leakage current plateau can be found in the later IeV measurements and the overall leakage current dramatically decreases about 2 magnitude. The growth of the resistance can also be confirmed in constant voltage and constant current curves as shown in Fig. 6(b). For the voltage set to be unchanged, the relationship between current and the resistance is inverse proportional in the basis of Ohm’s law. The current declines in the figure represents the improvement of resistance for composite film. When the current remains constant, there is a linear relationship between the voltage and the resistance. The resistance is speculated to be linear growth as the voltage shows a good linear curve. Based on the modification reaction model above, the increase of the resistance of the composite film is supposed to be generation of new interfacial AO layer and mending for defects. The IeV measurements for TEP-modified STO_nps@AO with different electrode thickness are prepared in Fig. 6(c). With Al top electrode about 65 nm, after remaining stable till ~200 MV/m the leakage current suddenly drops and then slightly grows until final breakdown occurs. The microscopic image of the sample after breakdown demonstrates the gray aluminum electrode is almost exhausted, where the circuit is cut off resulted in the drop of
Please cite this article as: W. Bi et al., Excellent energy density of crystalline SrTiO3@Amorphous Al2O3 nanocomposite combined with electrodeinduced interfacial reaction, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.153196
W. Bi et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
7
Fig. 5. (a) The anodic oxidation modification process model of composite film with Al electrode under high electric field. (b) Defects at the surface of TEP-modified STO_nps@AO sample without top electrode. (c) Defects in the interior TEP-modified STO_nps@AO sample without top electrode.
current in the graph. On the contrary, for Al top electrode thickness about 200 nm, the sudden drop of current at ~200 MV/m is erased. And a leakage current plateau can be detected which represents resistance improvement of composite film with new generated AO. When measurements finished, the Al electrode is intact except for the breakdown point at the spot of the test probe. Clearly, the top Al electrode takes part in the anodic oxidation reaction and the TEPmodified STO_nps@AO composite film with 200 nm Al top electrode embraces an excellent anodic oxidation capability. Fig. 6(d) shows the results of high-resolution XPS spectra analysis for Al 2p at electrode surface before and after IeV measurements. Before the tests, two peaks at 72.58 eV and 75.08 eV have been clearly found corresponding to metal state and oxide state of aluminum respectively, which shows the aluminum top electrode with a metallic oxide surface [24,39]. Yet after breakdown, the two peaks are replaced by one, which is at 74.11 eV corresponding to Al 2p of a new aluminum oxide [40]. The disappear of peak Al 2p from metal aluminum and the shift of the binding energy of Al 2p suggest that the top electrode takes part in the anodic oxidation modification process and a new AO is generated from this reaction. The above electrical measurements along with chemical analysis can be used as reasonable experimental evidences to testify that the newborn AO was created from anodic oxidation modification process. The FESEM cross section images of the sample before and after IeV measurements provides direct evidence for interfacial modification (Fig. 7). After IeV measurement, a dense
interface layer generated between the composite film and the Al top electrode can be seen with the consumption of Al electrode. Given the result of previous analysis and relevant studies, the newly interfacial layer is ascribed to be aluminum oxide from anodic oxidation reaction, whose resistivity and breakdown strength are ultra-high [41,42]. Moreover, the thickness of this new generated layer is proved to be reasonable according to that the thickness ratio of the oxide film to the aluminum layer replaced is about 0.725 [43]. According to above experimental analysis added with microstructure analysis, the interface modification model can be verified. Anodic oxidation is the major reaction mechanism where the newborn interfacial AO layer is the main characteristics. To further learn about the dielectric characteristics of the newborn anodic oxidation layer, impedance analysis methods are applied for this composite film with Al top electrode. IeV measurements from 0 V to 250 V are taken to produce the anodic oxidation layer while maintain the whole film intact. The Nyquist plots of (Al)TEP-modified STO_nps@AO sample before and after IeV measurement are shown separately in Fig. 8(a) and (b) with corresponding equivalent circuit mode and the fitting results. For Nyquist curves, the similar capacitive semicircle (Semicircle A) can be found in both before and after IeV measurement, which is correspond to composite film. However, after the measurement, data from lower frequency trends to form another capacitive semicircle (Semicircle B) which is regarded from the newly generated AO layer. According to the geometrical parameters of
Please cite this article as: W. Bi et al., Excellent energy density of crystalline SrTiO3@Amorphous Al2O3 nanocomposite combined with electrodeinduced interfacial reaction, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.153196
8
W. Bi et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
Fig. 6. (a) The I-E characteristics of repeating IeV measurements for the same (Al)TEP-modified STO_nps@AO sample. (b)Constant current (10 mA cm2) and constant voltage (40 V) for (Al)TEP-modified STO_nps@AO sample. (c) The IeV measurements of TEP-modified STO_nps@AO sample with Al top electrode of different thickness and the images for Al top electrode when the measurement finished. (d) High resolution XPS spectra of Al 2p peaks for composite film with Al top electrode before and after IeV measurements.
composite film and the newborn AO layer, the corresponding dielectric constant and resistivity can be calculated as shown in the tables, which basically conforms to testing data. The Bode plot is provided in Fig. 8(c). A plateau generated with a phase angle close to 90 explains the present system is close to a nearly ideal capacitor [44]. Similarly, plateau A correlated with capacitor system of composite film exists before and after IeV measurement. Base on the results of Nyquist plot, plateau B should arise at lower frequency, which shows capacitor behavior of newly generated anodic oxidation layer. The model based on above impedance analysis is
shown in Fig. 8(d). Before IeV measurement, the sample just include one capacitor system of composite film showing a highfrequency capacitor behavior. With application of electric field, newborn AO layer at the electrode-film interface provides a new capacitor system in low-frequency region. In all, applying Al as the top electrode, the new AO layer generated from anodic oxidation shows an ideal capacitor behavior with high resistance, which contributes greatly to improve the dielectric breakdown strength and showing an excellent interface modification effect.
Fig. 7. SEM cross-sectional micrographs of TEP-modified STO_nps@AO sample before and after IeV measurement.
Please cite this article as: W. Bi et al., Excellent energy density of crystalline SrTiO3@Amorphous Al2O3 nanocomposite combined with electrodeinduced interfacial reaction, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.153196
W. Bi et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
9
Fig. 8. Nyquist (impedance) plot with equivalent circuit mode and fitting results (a) (b), Bode plot (c) and model of impedance analysis (d) for the TEP-modified STO_nps@AO sample with Al top electrode before and after IeV measurement.
4. Conclusion In summary, composite dielectric film combining STO crystalline nanoparticles and amorphous AO is fabricated by spin coating process. With TEP added as a dispersing agent, the homogeneity and compatibility of the composite film have been effectively promoted, leading to more compact structure with less defects. After TEP modified, the composite structure embraces a good performance in dielectric constant and breakdown strength. However, adopting aluminum as the top electrode, a superior energy density of 12.2 J/cm3 with breakdown strength about 340 MV/m can be achieved. A fast discharge speed and a remarkable power density confirmed its availability in pulse energy storage device. The improvement of the composite film with Al top electrode is attributed to that the Al electrode can activate anodic oxidation under electric field which causes interface modification. An anodic oxidation interface modification model is provided based on varied measurements and a distinct newborn AO found in microstructure profile which exhibits excellent capacitive performances. Our
finding will provide an inspiring idea to design dielectric composite film assimilating the high breakdown strength of amorphous dielectrics and excellent dielectric constant of crystalline dielectrics. Besides, the remarkable anodic oxidation interface modification based on top electrode material can be applied in the composite film, which could promote the advanced development in energy storage materials and devices.
Author contribution statement Wei Bi: Methodology, Investigation, Validation, Formal analysis, WritingdOriginal draft. Manwen Yao: Conceptualization, Supervision, Project administration, Funding acquisition. Wenbin Gao: formal analysis, Resources, Writing-Review and Editing. Zhen Su: Formal analysis, Writing-Review and Editing. Xi Yao: Conceptualization, Project administration.
Please cite this article as: W. Bi et al., Excellent energy density of crystalline SrTiO3@Amorphous Al2O3 nanocomposite combined with electrodeinduced interfacial reaction, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.153196
10
W. Bi et al. / Journal of Alloys and Compounds xxx (xxxx) xxx
Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
[19]
[20] [21]
Acknowledgments [22]
This work is supported by the Joint Fund of the Ministry of Education of China under the grant number 6141A02022433. References [1] G.P. Awasthi, D. Kumar, B.K. Shrestha, J. Kim, K.S. Kim, H.P. Chan, C.S. Kim, Layer e structured partially reduced graphene oxide sheathed mesoporous MoS 2 particles for energy storage applications, J. Colloid Interface Sci. 518 (2018) 234. [2] M.S. Javed, C. Jie, C. Lin, X. Yi, C. Hu, Flexible full-solid state supercapacitor based on zinc sulfide spheres growing on carbon textile with superior charge storage, J. Mater. Chem. 4 (2015) 667e674. [3] Q. Wei, F. Xiong, S. Tan, L. Huang, E.H. Lan, B. Dunn, L. Mai, Porous onedimensional nanomaterials: design, fabrication and applications in electrochemical energy storage, Adv. Mater. 29 (2017) 1602300. [4] H.O.M.Y., P.S. Khiew, D. Isa, T.K. Tan, W.S. Chiu, C.H. Chia, A review of metal oxide composite electrode materials for electrochemical capacitors, Nano 9 (2014). -. [5] Z. Xie, B. Peng, S. Meng, Y. Zhou, Z. Yue, S.E. Trolier-Mckinstry, Z. Xie, B. Peng, S. Meng, Y. Zhou, Higheenergy-storage density capacitors of Bi(Ni1/2Ti1/2) O3ePbTiO3 thin films with good temperature stability, J. Am. Ceram. Soc. 96 (2013) 2061e2064. [6] W. Gao, M. Yao, Y. Xi, Substantially improved energy density of SrTiO3 thin film by cyclic cooling-heating and interfacial blocking effect, J. Mater. Chem. C 6 (2018), https://doi.org/10.1039/c8tc01748d. [7] B. Peng, Z. Xie, Z. Yue, L. Li, Improvement of the recoverable energy storage density and efficiency by utilizing the linear dielectric response in ferroelectric capacitors, Appl. Phys. Lett. 105 (2014), 242909-242224. [8] Z.M. Dang, J.K. Yuan, S.H. Yao, R.J. Liao, Flexible nanodielectric materials with high permittivity for power energy storage, ChemInform 25 (2013) 6334e6365. [9] J.Y. Li, L. Zhang, S. Ducharme, Electric energy density of dielectric nanocomposites, Appl. Phys. Lett. 90 (2007) 132901. [10] J.W. McPherson, K. Jinyoung, A. Shanware, H. Mogul, J. Rodriguez, Trends in the ultimate breakdown strength of high dielectric-constant materials, IEEE Trans. Electron Devices 50 (2003) 1771e1778. [11] L. Yao, Z. Pan, S. Liu, J. Zhai, H.H. Chen, Significantly enhanced energy density in nanocomposite capacitors combining the TiO2 nanorod array with poly(vinylidene fluoride), ACS Appl. Mater. Interfaces 8 (2016) 26343. [12] Z. Pan, L. Yao, J. Zhai, S. Bo, H. Wang, Significantly improved dielectric properties and energy density of polymer nanocomposites via small loaded of BaTiO 3 nanotubes, Compos. Sci. Technol. 147 (2017). S0266353817304049. [13] H. Tang, H.A. Sodano, Ultra high energy density nanocomposite capacitors with fast discharge using Ba0.2Sr0.8TiO3 nanowires, Nano Lett. 13 (2013) 1373e1379. [14] L. Yao, Z. Pan, J. Zhai, G. Zhang, Z. Liu, Y. Liu, High-energy-density with polymer nanocomposites containing of SrTiO3 nanofibers for capacitor application, Compos. Part A-Appl. S. 109 (2018) 48e54. [15] T. Haixiong, L. Yirong, A. Clark, H.A. Sodano, Nanocomposites with increased energy density through high aspect ratio PZT nanowires, Nanotechnology 22 (2011), 015702. [16] L. Fei, M. Yao, S. Zhen, J. Chen, P. Yong, Q. Li, Y. Xi, Enhancement of breakdown strength of SrTiO 3/nano-SiO 2 composite film prepared by sol-gel technology, Ceram. Int. 43 (2016). [17] X. Zhang, J. Jiang, Z. Shen, Z. Dan, M. Li, Y. Lin, C.W. Nan, L. Chen, Y. Shen, Polymer nanocomposites with ultrahigh energy density and high discharge efficiency by modulating their nanostructures in three dimensions, Adv. Mater. 30 (2018). [18] Z. Pan, L. Yao, J.W. Zhai, Y. Ke, S. Bo, H. Wang, Ultrafast discharge and highenergy-density of polymer nanocomposites achieved via optimizing the
[23]
[24]
[25] [26]
[27] [28]
[29] [30]
[31] [32] [33] [34]
[35]
[36]
[37]
[38]
[39]
[40] [41] [42] [43]
[44]
structure design of barium titanates, ACS Sustain. Chem. Eng. 5 (2017) acssuschemeng.7b00080. R. Thomas, D.C. Dube, M.N. Kamalasanan, S. Chandra, A.S. Bhalla, Structural, electrical, and low-temperature dielectric properties of solegel derived SrTiO3 thin films, J. Appl. Phys. 82 (1997) 4484e4488. H.H. Barrett, Dielectric breakdown of single-crystal strontium titanate, J. Appl. Phys. 35 (1964) 1420e1425. I. Burn, D.M. Smyth, Energy storage in ceramic dielectrics, J. Mater. Sci. 7 (1972) 339e343. P. Yong, M. Yao, J. Chen, K. Xu, Y. Xi, Electrical characteristics of SrTiO3/Al2O3 laminated film capacitors, J. Appl. Phys. 120 (2016), 08NA02. M. Yao, P. Yong, R. Xiao, Q. Li, Y. Xi, Enhanced self-repairing capability of solgel derived SrTiO3/nano Al2O3 composite films, Appl. Phys. Lett. 109 (2016) 202901. K.C. Chiang, C.H. Cheng, H.C. Pan, C.N. Hsiao, C.P. Chou, A. Chin, H.L. Hwang, High-temperature leakage improvement in metaleinsulatoremetal capacitors by workefunction tuning, IEEE Electron. Device Lett. 28 (2007) 235e237. Y. Matsumoto, Y. Matsumoto, Solid oxide electrochemical doping (SOED) method, Solid State Ion. 100 (1997) 165e168. J.P. Manceau, S. Bruyere, S. Jeannot, A. Sylvestre, P. Gonon, Metal-insulatormetal capacitors’ current instability improvement using dielectric stacks to prevent oxygen vacancies formation, Appl. Phys. Lett. 91 (2007) 2e262. G. Yip, J. Qiu, W.T. Ng, Z.H. Lu, Effect of metal contacts on the electrical characteristics of Al2O3 dielectric thin films, Appl. Phys. Lett. 92 (2008) 99. S. Zhen, M. Yao, L. Fei, P. Yong, F. Qian, Y. Xi, Microstructural transitions and dielectric properties of boron-doped amorphous alumina thin film, J. Mater. Sci. 52 (2017) 9314e9323. R.E. Mistler, E.R. Twiname, Surfactant Tape casting: theory and practice, Am. Ceram. Soc. (2015). S. Ogitani, S.A. Bidstrup-Allen, P.A. Kohl, Factors influencing the permittivity of polymer/ceramic composites for embedded capacitors, IEEE Trans. Adv. Packag. 23 (2000) 313e322. K.R. Mikeska, W.R. Cannon, Non-aqueous dispersion properties of pure barium titanate for tape casting, Colloids Surface. 29 (1988) 305e321. ndez-Sa ez, C. Navarro, On the estimation of percentiles of E. Barbero, J. Ferna the Weibull distribution, J. Mater. Sci. Lett. 18 (1999) 1441e1443. E. Barbero, J. Fern andez-S aez, C. Navarro, Statistical analysis of the mechanical properties of composite materials, Compos. B Eng. 31 (5) (2000) 375e381. L. Mengxin, Y. Manwen, S. Zhen, G. Wenbin, Y. Xi, Improved breakdown strength and energy density of Al2O3/nano-ZrO2 composite films via enhanced interfacial repairing behavior, Ceram. Int. (2018). S0272884218322788. C. Xu, L. Zhen, X. Chen, S. Yan, G. Wang, High charge-discharge performance of Pb0.98La0.02(Zr0.35Sn0.55Ti0.10)0.995O3 antiferroelectric ceramics, J. Appl. Phys. 120 (2016) 324. X. Ran, X. Zhuo, Y. Feng, X. Wei, J. Tian, Nonlinear dielectric and discharge properties of Pb0.94La0.04[(Zr0.56Sn0.44)0.84Ti0.16]O3 antiferroelectric ceramics, J. Appl. Phys. 120 (2016) 332. C. Pan, S. Wu, P. Li, J. Zhai, S. Bo, Great enhancement of energy storage density and power density in BNBT/BFO multilayer thin film hetero-structures, Inorg. Chem. Front. 5 (2018), 10.1039.C1038QI00487K. M. Yao, J. Chen, Z. Su, Y. Peng, P. Zou, X. Yao, Anodic oxidation in aluminum electrode by using hydrated amorphous aluminum oxide film as solid electrolyte under high electric field, ACS Appl. Mater. Interfaces 8 (2016) 11100e11107. Y.-C. Kim, H.-H. Park, J.S. Chun, W.-J. Lee, Compositional and structural analysis of aluminum oxide films prepared by plasma-enhanced chemical vapor deposition, Thin Solid Films 237 (1994) 57e65. H. He, K. Alberti, T.L. Barr, J. Klinowski, ESCA studies of aluminophosphate molecular sieves, J. Phys. Chem. 97 (1993) 13703e13707. H.J.D. Wit, C. Crevecoeur, The dielectric breakdown of anodic aluminum oxide, Phys. Lett. A 50 (1974) 365e366. J.R. Dickey, Improved dielectric properties for anodic aluminum oxide films by soft/hard two-step electrolytic anodization, ChemInform (1989) 20. J. Chen, M. Yao, R. Xiao, P. Yang, B. Hu, X. Yao, The application of the barriertype anodic oxidation method to thickness testing of aluminum films, Rev. Sci. Instrum. 85 (2014) 313e315. H. Berney, J. West, E. Haefele, J. Alderman, W. Lane, J.K. Collins, Chemical: a dna diagnostic biosensor: development, characterisation and performance, Sens. Actuator 68 (2000) 100e108.
Please cite this article as: W. Bi et al., Excellent energy density of crystalline SrTiO3@Amorphous Al2O3 nanocomposite combined with electrodeinduced interfacial reaction, Journal of Alloys and Compounds, https://doi.org/10.1016/j.jallcom.2019.153196