In0.05Nb0.05Ti0.90O12 composite ceramics: An effectively improved method to reduce the dielectric loss tangent and retain high dielectric permittivity

Journal Pre-proof CaCu3 Ti4 O12 /In0.05 Nb0.05 Ti0.90 O12 Composite Ceramics: An Effectively Improved Method to Reduce the Dielectric Loss Tangent and Retain High Dielectric Permittivity Sornram Otatawong, Jakkree Boonlakhorn, Supamas Danwittayakul, Prasit Thongbai

PII:

S0025-5408(19)32120-8

DOI:

https://doi.org/10.1016/j.materresbull.2019.110700

Reference:

MRB 110700

To appear in:

Materials Research Bulletin

Received Date:

17 August 2019

Revised Date:

23 October 2019

Accepted Date:

15 November 2019

Please cite this article as: Otatawong S, Boonlakhorn J, Danwittayakul S, Thongbai P, CaCu3 Ti4 O12 /In0.05 Nb0.05 Ti0.90 O12 Composite Ceramics: An Effectively Improved Method to Reduce the Dielectric Loss Tangent and Retain High Dielectric Permittivity, Materials Research Bulletin (2019), doi: https://doi.org/10.1016/j.materresbull.2019.110700

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CaCu3Ti4O12/In0.05Nb0.05Ti0.90O12 Composite Ceramics: An Effectively Improved Method to Reduce the Dielectric Loss Tangent and Retain High Dielectric Permittivity

Sornram Otatawong a, Jakkree Boonlakhorn a,b, Supamas Danwittayakulc, Prasit

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Thongbaia,b,* [email protected]

a

Department of Physics, Faculty of Science, Khon Kaen University, Khon Kaen

40002, Thailand

Institute of Nanomaterials Research and Innovation for Energy (IN-RIE(,

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b

NANOTEC-KKU RNN on Nanomaterials Research and Innovation for Energy, Khon

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Kaen University, Khon Kaen,0444 , Thailand c

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National Metal and Materials Technology Center, 114 Thailand Science Park,

Corresponding author (P. Thongbai)

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*

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Paholyothin Rd. Klong 1, Klong Luang, Pathumthani 12120, Thailand

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Graphical abstract

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Highlights

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CaCu3Ti4O12/In0.05Nb0.05Ti0.90O12 composite ceramics were prepared by SSR method. The mean grain size of CaCu3Ti4O12/In0.05Nb0.05Ti0.90O12 composites was reduced. tan

0.029-0.046 and

5.0 103-8.6 103 were achieved.

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4 ABSTRACT CaCu3Ti4O12/In0.05Nb0.05Ti0.90O12 (CCTO/INTO) composite ceramics with volume fraction ratios of 0.9/0.1 (10% INTO) and 0.8/0.2 (20% INTO) were prepared via a solid-state reaction method. XRD results indicated the mixed CaCu3Ti4O12 and TiO2 phases in the CCTO/INTO composite ceramics. The lattice parameter of the CCTO phase increased as the INTO composition increased, indicating the entry of some Nb5+ and/or In3+ ions into the CCTO lattice structure. The mean grain size of the

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CCTO/INTO composite ceramics was smaller than that of the CCTO ceramic,

demonstrating that the grain boundary mobility of the CCTO phase was decreased by

the INTO particles. Improved dielectric properties were achieved with a low dielectric

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loss tangent (0.029-0.046) in the CCTO/INTO composite ceramics, while high

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dielectric permittivities (5.0 103-8.6 103) were achieved. Nonlinear J-E behavior was demonstrated in the all-ceramic samples. The dielectric and nonlinear properties of

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layer capacitor effect.

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the CCTO and CCTO/INTO composite ceramics originated from an internal barrier

Keywords: CCTO/INTO composite ceramics; impedance spectroscopy; electrical

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properties; loss tangent; dielectric permittivity

5 1.

Introduction Dielectric materials play an important role in the development of various

technologies, especially electronic components. One of the most important electronic components is the ceramic capacitor. The development of a smaller capacitor has been extensively studied [1-20]. A dielectric material with a dielectric permittivity of > 103 plays an important role in such development. This material is called giant dielectric or colossal dielectric material.

researchers’ attention [1-9]. Although this material has an

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CaCu3Ti4O12 (CCTO) ceramics are giant dielectric materials that have attracted

> 044, the dielectric loss

tangent (tan ) value is 0.05 at 1 kHz [1, 2], which is not applicable for use as an

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electric capacitor. Therefore, the tan should be reduced before the material can be

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used as a capacitor. Studies focused on reducing the tan using various methods, such as doping with a suitable ion (for example, Mg2+ [8], Zn2+ [11], Ni2+ [9], and Sn4+

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[12]) or co-doping (for example, (Y3+, Al3+) [1], (Ni2+, Zr4+) [6], and (Sr2+, Ni2+) [13]). The primary role of these doping ions is to improve the intrinsic electrical properties

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of the grain boundaries. For example, substitution of Mg2+ or Ni2+ ions can increase the total resistivity of the grain boundaries by significantly enhancing the electrostatic

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potential barrier height at the individual grain boundary (GB) layers [8, 9]. Another widely studied method is fabricating CCTO-based composite oxides, such as

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CCTO/CaTiO3 and CCTO/TiO2 composites [14, 15, 21, 22]. The CCTO-based composites that have been studied and reported are CCTO/CaTiO3 and CCTO/TiO2 composites [14, 15, 21, 22]. Most recently, giant dielectric properties have been reported in various groups of co-doped TiO2 ceramics [10, 16-20]. The

of co-doped TiO2 ceramics was higher

than 104, while the tan was lower than 0.1 at 1 kHz. Furthermore, the

was slightly

6 dependent on the frequency from 102-106 Hz. Many factors contribute to the dielectric properties of co-doped TiO2 ceramics [10, 16-20]. One of the most important constituents, electron-pinned defect dipoles, occurs inside the grains. Sintering temperatures of 1400-1500 °C are required to fabricate co-doped TiO2 ceramics [10, 16, 17, 20]. Generally, materials with high electrical resistivity and low tan such as CaTiO3

tan . The

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and TiO2 oxides are used to fabricate high-permittivity materials with a reduced values of these two oxides are just below 500. The tan and

of CCTO

ceramics are significantly reduced by adding CaTiO3 and TiO2 phases [21, 22]. This is due to the low

values of CaTiO3 and TiO2 oxides. However, the dielectric

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properties and electrical response of CCTO/co-doped TiO2 composite ceramics have

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never been investigated and reported.

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In this study, co-doped TiO2/CCTO composites were fabricated to obtain a highpermittivity CCTO-based material with a low tan value sintered at a low temperature. The phase compositions, microstructural evolution, dielectric properties,

Experimental details

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and nonlinear J-E characteristics were investigated.

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2.1. Ceramic preparation The conventional solid-state reaction (SSR) method was used to prepare

CCTO and In0.05Nb0.05Ti0.90O12 (INTO) powders. Nb2O5 (99.99%), In2O3 (99.99%), TiO2 (99.99%), CuO (99.99%), CaCO3 (99.0% purity), and C2H5OH (99.5%) were the raw materials used to prepare the ceramic samples.

7 The preparation steps of the CCTO powder are as follows: First, the weight ratios for the raw materials were calculated using the chemical formula for CaCu3Ti4O12 and mixed via ball-milling in C2H5OH for 24 h. A rotation rate was ~150 rpm. The mixed raw material was then dried in an oven at 100 °C for ~24 h. The mixed powder was then ground and calcined at 900 °C for 12 h to obtain the CCTO powder. To prepare the INTO powder, the ball-milling (for 24 h) and drying steps

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were similar to the CCTO preparation, but the mixed powder was calcined at 1100 °C for 20 h.

To obtain the (1-x)CCTO-(x)INTO composite ceramics, calculated ratios

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between CCTO/INTO 0.9/0.1 (10% of INTO) and 0.8/0.2 (20% of INTO) were

weighed, and the mixed powders were ball-milled without the addition of C2H5OH

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(drying process) at a rotation rate of ~150 rpm for 6 h. The resulting powders were

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formed into green bodies using a method described in our previous work [10]. The CCTO, 0.9CCTO/0.1INTO, and 0.8CCTO/0.2INTO green bodies were sintered at

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1050 °C for 6 h. To easily compare the results between each sample, the sintered CCTO, 0.9CCTO/0.1INTO, and 0.8CCTO/0.2INTO ceramics are called the CCTO,

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CCTO-10INTO, and CCTO-20INTO ceramics, respectively.

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2.2. Structural, dielectric, and electrical characterizations The crystal structure and phase composition of the pure CCTO and

CCTO/INTO composite ceramics were characterized using an X-ray diffractometer (XRD, PANalytical, Empyrean). The XRD data were measured in the 2 range of 20 -80 with an increasing step of 0.02 /point. Rietveld refinement was carried out using X'Pert HighScore Plus software (PANalytical BV). The optimizing parameters

8 and coefficients can be obtained elsewhere [11]. The surface microstructures of the pure CCTO and CCTO/INTO composite ceramics were studied using desktop scanning electron microscopes (MiniSEM, SNE-4500M). The EDS analysis was performed via field emission scanning electron microscopy with an energy-dispersive Xray analysis (FESEM, Hitachi SU8030). The details of sample preparation for the dielectric and electrical measurements are described in our previous work [11]. For the dielectric measurements, the surfaces of the sintered ceramics were polished.

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Two parallel electrodes were obtained by sputtering Au (Polaron SC500). A Keysight E4990A impedance analyzer was used to test the dielectric properties of the sintered CCTO/INTO composite ceramics at an oscillation voltage (Vrms) of 500 mV.

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This measurement was performed in the frequency and temperature ranges of 40-107 Hz and -60 to 210 °C, respectively. Correlations between the current density (J) and

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electric field (E) were measured at room temperature (RT) using a high-voltage

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measurement unit (Keithley 247). The calculations of the dielectric and nonlinear J-E properties are described elsewhere [11].

Results and discussion

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The structural parameters, including the lattice parameter (ɑ) and grain size (G),

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are summarized in Table. 1. The first part of the structural section is the crystalline

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structure. As demonstrated in Fig. 1, single phases of CCTO (JCPDS 75-2188) and TiO2 (JCPDS 21-1276) were detected in the CCTO and INTO ceramics, respectively [10, 23]. No impurity phases of the related Ca, Cu, and Ti elements were observed. A mixed CCTO-TiO2 phase was clearly detected in the CCTO-10INTO and CCTO20INTO ceramics, signifying the combination of the CCTO and INTO phases in the composite samples. This result is consistent with reports of other composite systems

9 [14, 21, 22]. In this work, for the CCTO/INTO composite ceramics, the ɑ values of both the CCTO and TiO2 phases were simultaneously calculated using the Rietveld method. As listed in Table 1, the ɑ values of the CCTO, CCTO-10INTO, and CCTO20INTO composite ceramics and INTO ceramic samples were near the values reported in other studies of CCTO and INTO ceramics [10, 23]. Interestingly, for the CCTO phase, the ɑ value increased as the INTO composite phase increased. Concurrently, the ɑ value of the TiO2 phase in the CCTO-10INTO and CCTO-

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20INTO ceramics decreased compared to the ɑ value of the INTO sample. It is possible that Nb5+ and/or In3+ in the INTO powder diffused from the INTO phase and moved to substitute in suitable sites of the CCTO structure during the sintering

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process. The most likely site at which Nb5+ and/or In3+ can substitute in the CCTO lattice is the Ti4+ site. This is because the oxidation states of Nb5+ and/or In3+ are

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closer to that of Ti4+. In addition, the ionic radii of Ti4+ (r6=0.605 Å) are also near the

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ionic radii of Nb5+ (r6=0.64 Å) and In3+ (r6=0.80 Å) [24]. As Fig. 1 shows, the XRD result supports the assumption of Nb5+ and/or In3+ substitution in the Ti4+ sites. This is because, if these two ions were to replace in Cu2+ and/or Ca2+ sites, the related Cu and

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Ca impurity phases must appear. The increase in the ɑ value of the CCTO phase is similar to the that in (In3+ and Nb5+) co-doped CCTO ceramics [25].

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The ceramic microstructure was systematically studied. The surface

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microstructures and grain size distributions of the sintered ceramics are shown in Fig. 2. The mean grain sizes of the CCTO-10INTO and CCTO-20INTO ceramics were obviously smaller than those of the CCTO ceramic. The mean grain size of the CCTO/INTO composite ceramics significantly decreased as the composition of INTO increased. The first factor in the decrease in the grain size was mixed with the codoped TiO2 ceramic, which has a higher melting temperature than the CCTO ceramic.

10 The mixing with the co-doped TiO2 ceramic had an influence on blocking the grain growth mechanism throughout the sintering process. This result corresponds to reports of CaCu3Ti4O12/CaTiO3 and CaCu3Ti4O12/TiO2 composite ceramics [21, 22]. The second factor can be described by the XRD results. The possible factor in the decrease in the grain size in the CCTO/INTO composite ceramics is the influence of a solute drag mechanism. The XRD result indicates that some parts of the Nb5+ and/or In3+ diffused into the CCTO lattice. The grain growth behavior observed in this work

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may originate from the mismatch between the ionic radii of the Nb5+ and/or In3+ and the main elements of CCTO ceramics, which can cause lattice strain energy during the sintering process and results in a decrease in the grain size of CCTO/INTO composite

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ceramics [25]. A few pores were observed in the CCTO-20INTO ceramic. It is

important to note that porosity is a crucial parameter for ceramic capacitors’

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performances. The percentages of the linear shrinkage in the sintered CCTO,

6.99%, respectively.

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0.9CCTO/0.1INTO, and 0.8CCTO/0.2INTO ceramics were 11.98, 8.49, and

The EDS spectra and the scanning area of the CCTO-20INTO ceramic are shown

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in Fig. 3 and its inset, respectively. This figure confirms the presence of the Nb and In dopants as well as the Ca, Cu, Ti, and O main elements in the CCTO-20INTO

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ceramic. The dispersions of the main and doping elements are shown in Fig. 4.

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Clearly, In, Nb, and O ions are thoroughly spread in the CCTO/INTO composite ceramics. This result supports the increase in the ɑ value due to the substitution of Nb5+ and/or In3+ in the CCTO lattice as well as the decrease in the mean grain size of the composite ceramics from the influence of a solute drag mechanism [25]. Therefore, the decrease in the grain size may have originated from the influences of both the mixed INTO phase and the solute drag effect [22, 25]. The darker regions in

11 the SEM mapping of the Ca and Cu ions indicated by the yellow cursors shown in Fig. 4(a) and (b) confirm the very low amounts of these two elements in this area. Simultaneously, as shown in Fig. 4(c), the brighter area, which corresponds to the dark areas in Fig. 4(a) and (b), shows the higher density of the Ti ions compared to other regions. These darker/brighter areas display the INTO phase in the composite ceramics. Consequently, the mixed CCTO/INTO phases were openly proven in this way.

frequency dependence of

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The dielectric and electrical parameters are summarized in Table 2. The in the CCTO, CCTO-10INTO, and CCTO-20INTO

ceramics is shown in Fig. 5. Interestingly, the low-frequency

of both the CCTO-

However, the

value significantly decreased with the increasing INTO concentration. value of the CCTO-10INTO and CCTO-20INTO ceramics remained

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Clearly, the

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10INTO and CCTO-20INTO ceramics decreased compared to the CCTO ceramic.

Hz, the

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at a giant dielectric response level [11]. Additionally, in a frequency range of 40-106 frequency stability of the CCTO-10INTO and CCTO-20INTO ceramics

Hz,

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was better than that of the undoped CCTO ceramic. In the frequency range of 105-106 rapidly decreased as the frequency increased, which indicated a dielectric

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relaxation behavior due to a dielectric response inside the grains [4-6]. The

values

at 1 kHz and 20 °C of the CCTO, CCTO-10INTO, and CCTO-20INTO ceramics were

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6.9 104, 8.6 103, and 5.0 103, respectively. Combining the

with the SEM images,

the dielectric properties of the CCTO-based ceramics are associated with an internal barrier layer capacitor (IBLC) effect. This result is similar to those reported in the literature [4-6, 8, 9]. Furthermore, the lowest

value of the CCTO-20INTO

ceramic was also attributed to the appearance of pores in its microstructure. The frequency dependence of the tan of these three ceramics is shown in inset (1) of Fig.

12 5; the tan of both the CCTO-10INTO and CCTO-20INTO ceramics was lower than that of the CCTO ceramic in a frequency range of 40-105 Hz. According to the SEM and SEM mapping images, the decrease in the tan , which corresponded to a decrease in the DC conduction (

dc),

may have been caused by the increase in the total GB

resistance (Rgb) due to the increase in the GB layer per unit volume and the presence of the insulating INTO phase. The tan values at 1 kHz and 20 °C of the CCTO, CCTO-10INTO, and CCTO-20INTO ceramics were 0.100, 0.029, and 0.046, with the tan indicated that the best dielectric

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respectively. Combining the

properties were achieved in the CCTO-10INTO ceramic, which provided a very high ( 8.6 103) and a low tan (~0.029). The decrease in the tan of the CCTO/INTO

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ceramics was consistent with reports on other composite systems [21, 22]. The

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nonlinear current density (J) electric field (E) relationships of the sintered ceramics are displayed in inset (2) of Fig. 5. As shown in this figure, the nonlinear relationship

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between J and E was readily apparent and indicated the electrical response of the GBs due to specific behavior of an IBLC structure [4, 6, 26]. As a result, the IBLC effect

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was the main origin of the giant dielectric response of the CCTO-based ceramics. To prove the origin of the dielectric and electrical responses of the CCTO/INTO

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ceramics, impedance and admittance spectroscopy and the electrical modulus were used to separate the electrical responses of the insulating and semiconducting parts.

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Accordingly, the grain resistance (Rg) and Rgb was obtained. The complex impedance (Z*), admittance (Y*), and electrical modulus (M*) were calculated using the following:

Z* Z

iZ

1 j C0 *

1 j C0 (

i )

,

Y* = Y + jY = 1/Z*,

(1) (2)

13 M*= M + jM = 1/ *, where Z , Y , M , and Z , Y , M , and permittivity,

(3) are the real parts of Z*, Y*, M*, and *, respectively and

are the imaginary parts. * is the complex dielectric

= tan is the total loss factor, =2 f is the angular frequency, and

C0= 0A/d is the capacitance of the free space. Rg and Rgb can be estimated from the nonzero intercept and diameter of the large semicircle arc of the impedance

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complex Z* plot, respectively [11]. The impedance complex Z* plots at 110 °C of the CCTO, CCTO-10INTO, and CCTO-20INTO ceramics are shown in Fig. 6 and inset (1). Rgb of both the CCTO-10INTO and CCTO-20INTO ceramics were

enhanced by mixing with the INTO phase. The Rgb of the CCTO, CCTO-10INTO,

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and CCTO-20INTO ceramics were 4.98 103, 4.24 105, and 2.42 105

cm,

0

where

s

1 , C R s 0 gb

(4)

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tan

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respectively. The relationship between the low-frequency tan and Rgb follows:

is the dielectric permittivity in a low-frequency range. This equation

dc

[8, 9]. As demonstrated in inset (2) of Fig. 6, the Rg values of the

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the decrease in

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indicates the origin of the decrease in low-frequency tan , which can be promoted by

sintered ceramics were slightly different. The Rg values of the CCTO, CCTOcm, respectively.

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10INTO, and CCTO-20INTO ceramics were 112, 93, and 119

The combinations of spectroscopic plots for Z and M are effective methods

that have usually been employed to characterize electrical components (phases) in polycrystalline ceramics [27]. For CCTO and related oxides, the relaxation peaks of Z and M that resulted from the electrical response of semiconducting grains appear in low-temperature (<-90 oC) and high-frequency (>105 Hz) ranges

14 [28]. Unfortunately, in this study, such relaxation peaks cannot be observed over the measured temperature and frequency ranges. According to our previous research [29], the electrical response of the semiconducting grains for Na1/2Y1/2Cu3Ti4O12 ceramics can be characterized by admittance spectroscopy analysis. Thus, the combined spectroscopic plots of Z , M , and Y were used to further clarify the electrical responses of the CCTO/INTO composite ceramics. As shown in Fig. 7(a), in a low-frequency range, fmax of a Debye-type peak in the

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Z plot must appear below 40 Hz, indicating that the CCTO/INTO composites

are too resistive to measure at -50 oC [27]. In a high-frequency range, a Debyetype peak in the M plot cannot be observed, while fmax in the Y plot can be

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observed at 650 kHz, indicating the electrical response of the grains [29]. To

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shift fmax of the Debye peaks for the high-resistive phase in the measured frequency range, the resistivity must be reduced by increasing the temperature

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measurements. At 50 oC, a low-frequency fmax of any Debye-type peak in the M and Z plots disappeared, while a high-frequency fmax in Y plot moved out of

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the higher limit frequency range due to the decreased resistivity of the grains. As the temperature increased to 150 oC (Fig. 7(c)), fmax of a Debye-type peak in the

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M and Z plots occurred in the frequency range of 103-104 Hz and shifted to a high-frequency range of 104-105 Hz as the temperature increased to 200 oC, as

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shown in Fig. 7(d). The highly resistive phase was caused by the insulating GBs. The variations in Rg and Rgb as the temperature increased are illustrated in Fig.

8(a) and its inset. Rg and Rgb declined significantly as the temperature increased. This electrical response is the general behavior of CCTO ceramics [1, 5, 11]. The calculation of the conduction activation energies of the grains (Eg) and GBs (Egb) was conducted using the Arrhenius law:

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Rg , gb

R0 exp

Eg , gb k BT

,

(5)

where R0, kB, and T are the pre-exponential constant term, the Boltzmann constant, and the absolute temperature, respectively. The temperature dependence of Rg and Rgb can be well fitted by the Arrhenius law. Using Eq. (5), the slopes obtained by

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linearly fitting the lines were used to calculate the Eg and Egb values of the sintered ceramics. As listed in Table 2, the Eg of the CCTO, CCTO-10INTO, and

CCTO-20INTO ceramics was in the range of 0.075-0.085 eV. The Egb values were

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0.655, 0.714, and 0.592 eV for the CCTO, CCTO-10INTO, and CCTO-20INTO

ceramics, respectively. The large difference between the Eg and Egb values indicates

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the formation of an IBLC in the CCTO/INTO ceramics [30].

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The relative Rgb can be calculated using the Arrhenius law together with the Egb and R0 values. As shown in Fig. 9, the experimented Rgb (solid symbol) and the calculated Rgb matched well. The exponential decrease in Rgb as the temperature

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increased can be clearly seen in all of the CCTO/INTO ceramics. Interestingly, as shown in the inset, the tan at 1 kHz and 20 °C was inversely proportional to the Rgb

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at the same temperature. The decrease in Rgb due to the increase in the temperature

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indicates the thermally activated electrical response of the GBs, resulting in a strong increase in the low-frequency

4.

in the high-temperature range.

Conclusions This study investigated the structure and properties of

CaCu3Ti4O12/In0.05Nb0.05Ti0.90O12 (CCTO/INTO) composite ceramics. The structural

16 characterization demonstrated that the CCTO and INTO phases mixed well. The SEM and mapping images showed the influence of the INTO phase and the solute drag effect caused by the Nb5+ and In3+, which inhibited the grain growth rate during sintering. High dielectric permittivity (~5.0 103-8.6 103) and low tan (~0.0290.046) were achieved in the composite ceramics. The largely reduced tan in the CCTO/INTO ceramics was associated with the enhanced GB response. The results obtained via impedance spectroscopy and the nonlinear J-E measurements indicated

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the formation of an internal barrier layer capacitor in the CCTO ceramic.

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Declaration of interests

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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.

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The authors declare the following financial interests/personal relationships which may

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be considered as potential competing interests:

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Acknowledgments

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This study was financially supported by the Synchrotron Light Research Institute, Khon Kaen University, and the Thailand Research Fund (TRF) (Grant No. BRG6180003). This work was partially supported by the Research Network NANOTEC (RNN) program of the National Nanotechnology Center (NANOTEC), NSTDA, the Ministry of Science and Technology, and Khon Kaen University,

17 Thailand. S. Otatawong thanks the Thailand Graduate Institute of Science and

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ro of

Technology (TGIST) for his MSc scholarship.

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CaCu3(Ti1−xSnx)4O12 ceramics, Mater. Chem. Phys. 124(2-3) (2010) 982-986. [13] S. Rhouma, S. Saîd, C. Autret, S. De Almeida-Didry, M. El Amrani, A.

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Megriche, Comparative studies of pure, Sr-doped, Ni-doped and co-doped

(2017) 121-126.

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CaCu3Ti4O12 ceramics: Enhancement of dielectric properties, J. Alloys Compd. 717

[14] J.A. Cortés, G. Cotrim, S. Orrego, A.Z. Simões, M.A. Ramírez, Dielectric and

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non-ohmic properties of Ca2Cu2Ti4-xSnxO12 (0.0 ≤ x ≤4.0) multiphasic ceramic composites, J. Alloys Compd. 735 (2018) 140-149.

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[15] X. Ouyang, M. Habib, P. Cao, S. Wei, Z. Huang, W. Zhang, W. Gao, Enhanced

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extrinsic dielectric response of TiO2 modified CaCu3Ti4O12 ceramics, Ceram. Int. 41(10, Part A) (2015) 13447-13454. [16] B. Guo, P. Liu, X. Cui, Y. Song, Enhancement of breakdown electric field and DC bias of (In0.5Nb0.5)0.005(Ti1-xZrx)0.995O2 colossal permittivity ceramics, J. Alloys Compd. 740 (2018) 1108-1115.

20 [17] Y. Yu, Y. Zhao, T.-D. Zhang, R.-X. Song, Y.-L. Zhang, Y.-L. Qiao, W.-L. Li, W.-D. Fei, Low dielectric loss induced by coupling effects of donor-acceptor ions in (Nb+Al) co-doped rutile TiO2 colossal permittivity ceramics, Ceram. Int. 44(6) (2018) 6866-6871. [18] X. Zhu, L. Yang, J. Li, L. Jin, L. Wang, X. Wei, Z. Xu, F. Li, The dielectric properties for (Nb,In,B) co-doped rutile TiO2 ceramics, Ceram. Int. 43(8) (2017) 6403-6409.

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[19] C. Yang, M.Y. Tse, X. Wei, J. Hao, Colossal permittivity of (Mg + Nb) co-doped TiO2 ceramics with low dielectric loss, Journal of Materials Chemistry C 5(21) (2017) 5170-5175.

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[20] W. Hu, Y. Liu, R.L. Withers, T.J. Frankcombe, L. Norén, A. Snashall, M.

Kitchin, P. Smith, B. Gong, H. Chen, J. Schiemer, F. Brink, J. Wong-Leung, Electron-

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Mater. 12(9) (2013) 821-826.

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pinned defect-dipoles for high-performance colossal permittivity materials, Nat.

[21] J. Jumpatam, P. Thongbai, B. Kongsook, T. Yamwong, S. Maensiri, High permittivity, low dielectric loss, and high electrostatic potential barrier in

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Ca2Cu2Ti4O12 ceramics, Mater. Lett. 76 (2012) 40-42. [22] K. Prompa, E. Swatsitang, C. Saiyasombat, T. Putjuso, Very high performance

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dielectric and non-Ohmics properties of CaCu3Ti4.2O12 ceramics for X8R capacitors,

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Ceram. Int. 44(11) (2018) 13267-13277. [23] M.A. Subramanian, D. Li, N. Duan, B.A. Reisner, A.W. Sleight, High Dielectric Constant in ACu3Ti4O12 and ACu3Ti3FeO12 Phases, J. Solid State Chem. 151(2) (2000) 323-325.

21 [24] R.D. Shannon, Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides, Acta Crystallographica Section A 32(5) (1976) 751-767. [25] J. Boonlakhorn, P. Kidkhunthod, P. Thongbai, Effects of Co–Doping on Dielectric and Electrical Responses of CaCu3Ti4-x(Nb1/2In1/2)xO12 Ceramics, Journal of Physics: Conference Series 901(1) (2017) 012078. [26] S.-Y. Chung, I.-D. Kim, S.-J.L. Kang, Strong nonlinear current–voltage

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[27] M. Li, D.C. Sinclair, Transformation from insulating p-type to semiconducting n-

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type conduction in CaCu3Ti4O12-related Na(Cu5/2Ti1/2)Ti4O12 ceramics, J. Appl. Phys. 114(3) (2013) 034106.

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[28] J. Liu, C.-G. Duan, W.-G. Yin, W. Mei, R. Smith, J. Hardy, Large dielectric

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Thongbai, S. Maensiri, Non-Ohmic Properties and Electrical Responses of Grains and Grain Boundaries of Na1/2Y1/2Cu3Ti4O12 Ceramics, J. Am. Ceram. Soc. 100(1) (2017)

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[30] D.C. Sinclair, T.B. Adams, F.D. Morrison, A.R. West, CaCu3Ti4O12: One-step internal barrier layer capacitor, Appl. Phys. Lett. 80(12) (2002) 2153.

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22

23 Table 1.

Lattice parameters (ɑ) of the CCTO structures and the mean grain sizes (G) of the CCTO, CCTO-10INTO, and CCTO-20INTO ceramics

Sample

CCTO

CCTO-10INTO

CCTO-20INTO

ɑ CCTO (a=b=c) (Å)

7.392 (2)

7.396 (9)

7.400 (6)

ɑ TiO2 (a=b) (Å)

4.595 (4)

4.596 (5)

4.598 (1)

ɑ TiO2 (c) (Å)

2.957 (3)

2.962 (2)

2.965 (4)

3.70 0.88

2.59 0.67

4.94 1.53

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G ( m)

INTO

and tan at 1 kHz and 20 °C, Rg at 20 °C, Rgb at 110 °C, activation energies of the grains (Eg) and GBs (Egb), breakdown electric

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Table 2.

f

24

tan

Rg (

68955

0.100

112

CCTO-10INTO

8642

0.029

93

CCTO-20INTO

5013

0.046

119

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Eg (eV)

Egb (eV)

Eb (V/cm)

4.98 103

0.075

0.655

196

4.46

4.24 105

0.075

0.714

153

2.05

0.084

0.592

2634

5.01

Rgb (

Pr

CCTO

cm)

cm)

e-

Sample

pr

field (Eb), and nonlinear coefficients ( ) of the CCTO, CCTO-10INTO, and CCTO-20INTO ceramics

2.42 105

25 FIGURE CAPTIONS Fig. 1.

XRD patterns of the (a) CCTO, (b) CCTO-10INTO, (c) CCTO-20INTO, and

(d) INTO ceramics.

+(433)

+(440)

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(301) (112)

+(422) (002) (310)

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(b)

30

40

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(a)

20

(211) (220)

+(400)

(210) +(321)

+(222)

(c)

(200) (111)

(d)

+(013)

(101)

+(220)

* TiO2

+(211)

Intensity (arb. unit)

(110)

+ CaCu3Ti4O12

50

60

70

80

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2 (Deg.)

SEM images and size distributions of the (a) CCTO, (b) CCTO-10INTO,

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Fig. 2.

and (c) CCTO-20INTO ceramics.

26 (a) CCTO

(b) CCTO 10INTO

(c) CCTO 20INTO

5 m

21 14 7 0

2

4

6

8

24

CCTO 10INTO

20 16 12 8 4 0

3

4

5

Grain size ( m)

18 9 0

1

2

3

Grain size ( m)

Fig. 3.

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Grain size ( m)

2

CCTO 20INTO 27

EDS spectrum measured on the surface area of the CCTO-20INTO ceramic;

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the inset shows the selected space.

4

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CCTO

5 m

Relative frequency (%)

28

Relative frequency (%)

Relative frequency (%)

5 m

CCTO 20INTO

27

Fig. 4.

Elemental distributions of the (a) Ca, (b) Cu, (c) Ti, (d) O, (e) Nb, and (f) In

at the surface of the CCTO-20INTO ceramic.

(d) O

(e) Nb

(c) Ti

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(b) Cu

(f) In

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(a) Ca

Fig. 5.

Frequency dependence of

at 20 °C of the CCTO, CCTO-10INTO, and

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CCTO-20INTO ceramics; insets (1) and (2) show the frequency dependence of the tan at 20 °C and the nonlinear J-E properties at room temperature, respectively.

28

105 104

0.5 0.4

2

101 100

tan

10

CCTO CCTO 10INTO CCTO 20INTO @ 20 oC

0.3

(1)

CCTO 20INTO @ 20 oC

0.2

45

J (mA/cm2)

'

10

CCTO 10INTO

0.1 0.0

102

102

103 104 Frequency (Hz)

105

103

36 27

CCTO CCTO 10INTO CCTO 20INTO @ RT

(2)

18 9 0 102

104

104

105

106

Impedance complex Z* plots of the CCTO, CCTO-10INTO, and CCTO-

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Fig. 6.

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Frequency (Hz)

103 E (V/cm)

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CCTO 3

20INTO ceramics at 110 °C; insets (1) and (2) show the enlarged Z* plot of the CCTO

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respectively.

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ceramic at this temperature and the high-frequency Z* plot at 20 °C of these ceramics,

29 5

320

CCTO fitting curve @ 110 oC

4

Z'' ( .cm)

.cm)

40

Z'' (103

.cm)

3

30

2 1 0

1

2

3

4

Z' (

Z'' (104

240 160 80

(1) 0

CCTO CCTO 10INTO CCTO 20INTO @ 20 oC

5

6

(2)

0 0

7

40

80 120 Z' ( .cm)

.cm)

160

20

10

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CCTO CCTO 10INTO CCTO 20INTO fitted curves @ 110 oC

0 0

10

20

30

Z' (104

40

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.cm)

50

Frequency dependence of M , Z , and Y for the CCTO-10INTO ceramic at

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Fig. 7.

(a) -50 oC, (b) 100 oC, (c) 150 oC, and (d) 200 oC. 6

4x10

6

3x10

6

CCTO-10INTO

-3

1.0x10

-3

8.0x10

-4

6.0x10

-4

(b)

8.0x10

-5

6.0x10

-5

2x10

1x10

6

4.0x10

6

2.0x10

-4

4.0x10

-5

RgbCgb ?

2.0x10

M'' Z'' Y''

-4

-5

0.0

0

3

4

5

RgbCgb

0

0.0

2

6

4

2x10

4

-5

-3

-5

4

3

2.0x10

o

150 C

0

0.0

2

3

4

5

Log(f / Hz)

-3

-3

1.0x10

4

5

-3

6

5.0x10

-5

4.0x10

-5

3.0x10

-5

2.0x10

-5

1.0x10

-5

RgbCgb

RgCg

4x10

3

3x10

3

2x10

3

1.2x10

-2

9.0x10

-3

6.0x10

1x10

3

-3

3.0x10

-3

o

200 C 0.0

0.0

0

2

3

4

5

0.0

6

Log(f / Hz)

(a) Impedance complex Z* plots of the CCTO-20INTO ceramic in a

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Fig. 8.

6

-3

-3

2.0x10

Log(f / Hz)

(d)

M''

4.0x10

-3

3.0x10

-1

1x10

1.0x10

-3

6.0x10

-1

ur 2.0x10

8.0x10

-3

4.0x10

Y'' (S.cm )

M''

3x10

RgCg

-3

5.0x10

0.0

-Z'' ( .cm)

-5

Y'' (S.cm )

-5

3.0x10

-Z'' ( .cm)

4.0x10

6

6.0x10

50 C

Log(f / Hz)

(c)

2x10

6

o

-50 C

2

6

1x10

o

0.00

6

3x10

-1

M'' Z'' Y''

-5

4x10

RgCg

-1

2.50x10

1.2x10

na

M''

5x10

RgCg

-Y'' (S.cm )

5.00x10

-5

RgbCgb ?

-Z'' ( .cm)

-5

Y'' (S.cm )

-4

7.50x10

-Z'' ( .cm)

1.00x10

M''

(a)

temperature range of 80 °C-130 °C; the inset shows the impedance complex Z* plots of this ceramic in a low-temperature range. (b) and (c) show the Arrhenius plots of Rgb of the CCTO, CCTO-10INTO, and CCTO-20INTO ceramics.

30

16 12

(b) 6.0

50 oC 40 oC 30 oC 20 oC 10 oC

20 15 10

CCTO CCTO 10INTO CCTO 20INTO

5.6

Ln(Rg)

Z'' (102

20

.cm)

80 oC 90 oC 100 oC 110 oC 120 oC 130 oC fitted curves CCTO 10INTO

24

5

5.2 4.8 4.4

0 0

2

4

Z' (102

6

8

3.6

10

3.9

4.2

8 4

(c)

14 10

12 8

CCTO CCTO 10INTO CCTO 20INTO

6

0

4

0

5

10

15

25

30

2.1

2.4

2.7

3.0

3.3

1000/T (K )

.cm)

Fig. 9.

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Z' (105

20

4.5

1000/T (K )

.cm)

Ln(Rgb)

Z'' (105

.cm)

(a)

Temperature dependence of Rgb of the CCTO, CCTO-10INTO, and CCTO-

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20INTO ceramics; the solid and open symbols show the experimented Rgb and

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calculated Rgb at 20 °C.

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calculated Rgb, respectively. The inset shows the relationship between the tan and

31

1010

0.12

1013 tan

107

0.06

106

0.03

109

0.00

105 0

107

10

20

104

% INTO

105 10

CCTO CCTO 10INTO CCTO 20INTO

3

101

-40

0

40

80

120

ro of

Rgb ( .cm)

108

tan

11

Rgb ( .cm)

10

109

Rgb

0.09

160

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Temperature (oC)

200