- Email: [email protected]
Strong photoluminescence and good electrical properties in Eu-modified SrBi2Nb2O9 multifunctional ceramics
Ceramics International 42 (2016) 14849–14854
Contents lists available at ScienceDirect
Ceramics International journal homepage: www.elsevier.com/locate/ceramint
Strong photoluminescence and good electrical properties in Eumodified SrBi2Nb2O9 multifunctional ceramics Lei Yu a, Jigong Hao a,n, Zhijun Xu a, Wei Li a, Ruiqing Chu a,n, Guorong Li b a
College of Materials Science and Engineering, Liaocheng University, Liaocheng 252059, People's Republic of China The State Key Lab of High Performance Ceramics and Superfinemicrostructure, Shanghai Institute of Ceramics, Chinese Academy of Science, Shanghai 200050, People’s Republic of China b
art ic l e i nf o
a b s t r a c t
Article history: Received 1 June 2016 Received in revised form 17 June 2016 Accepted 19 June 2016 Available online 23 June 2016
Bismuth layer-structured ferroelectric (BLSFs) ceramics of Sr1 xEux Bi2Nb2O9 (SBT-xEu, x ¼0.000, 0.002, 0.004, 0.006) were prepared by a conventional solid-state reaction method. All the samples have a bismuth oxide layered structure with a dense microstructure. The ferroelectric, piezoelectric, dielectric and optical properties of the ceramics were investigated. After Eu3 þ doping, samples show a bright red photoluminescence upon blue light excitation of the 400–500 nm. Upon the excitation of 465 nm light, the materials have two intense emission bands peaking around 593 nm (yellow) and 616 nm (red). Meanwhile, good electrical properties with large piezoelectric constant d33 of 14 pC/N and large remnant polarization 2Pr of 11.97 μC/cm2 are obtained at x ¼ 0.006. Moreover, this material has a high Curie temperature (Tc ¼ 429 °C) and high resistivity, which makes the material resistant to thermal depolarization up to its Curie temperature. This feature indicates that the SBN-xEu ceramics have a latent use in high temperature applications. & 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Keywords: Bismuth layer-structured ferroelectric Photoluminescence Excitation Red emission Curie temperature
1. Introduction Aurivillius bismuth-layer structure ferroelectrics (BLSFs) have received significant attention for the latent use in high-temperature sensors, non-volatile random access memory (NVRAM) and piezoelectric resonators due to their high Curie temperature, low dielectric constant, low aging rate and anisotropic electromechanical coupling factors [1,2]. BLSFs compounds have the general formula (Bi2O2)2 þ (Am 1BmO3m þ 1)2–, where A is a mono-, di- or tri-valent ions (or their combination) such as Sr2 þ , Ca2 þ etc, B is tetra-, penta-, or hexa-valent ions (or their combination) with appropriate size such as Ti4 þ , Nb5 þ etc, and m is number of pseudo-perovskite (Am 1BmO3m þ 1)2– layers which varies from 1 to 5 [3–5]. The crystal structure of BLSF can be described as perovskite-like (Am 1BmO3m þ 1)2 layers interleaved with bismuth oxide (Bi2O2)2 þ layers units along the c-axes [6,7]. While the perovskite-like layers offer large possibilities in terms of compositional flexibility, it could incorporate various cations such as Na þ , K þ , Ca2 þ , Sr2 þ , Ba2 þ for the A-site and Ti4 þ , Nb5 þ , W6 þ for the B-site. The cation sites in the interleave (Bi2O2)2 þ layers are almost exclusively occupied by Bi3 þ cations forming (Bi2O2)2 þ slabs. Some cations, include the above mentioned cations and the n
Corresponding authors. E-mail addresses: [email protected] (J. Hao), [email protected] (R. Chu).
http://dx.doi.org/10.1016/j.ceramint.2016.06.119 0272-8842/& 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
rare earth ions (RE3 þ , such as Er3 þ , Eu3 þ , Ho3 þ , Pr3 þ etc), could improve the properties of the BLSFs. The RE3 þ ions are always regarded as the luminous centers to design a large number of luminescent materials due to their special electronic structure [8]. Owing to the luminescent behavior of RE3 þ , BLSFs modified by RE3 þ show novel photoluminescence properties besides retaining the ferroelectric functions [9]. In addition, the Bi3 þ ion can function as both an activator and a sensitizer to develop phosphors for the photoluminescence materials [10,11]. Along with the intensive development of microelectronic devices toward multiple functions, it is of interest and significance to study the potential luminescent properties of RE3 þ doped BLSFs for multifunctional material applications. SrBi2Nb2O9 (SBN) ceramics have a typical layer-structured ferroelectrics (m ¼2). Yao et al. [12] reported that the SBN sample shows a high Curie temperature (444 °C), low dielectric loss tanδ (1.47%) and temperature-insensitive large piezoelectric coefficient. This material is believed to be a very promising candidate for high temperature applications. Additionally, it was found that the Eu3 þ ion exhibited bright red emission at room temperature upon blue light excitation of the 400–500 nm [13]. The Eu3 þ ion occupy the A-site (Sr2 þ ) of SrBi2Nb2O9 ceramic [14], which may be very helpful to improve the performance of the SBN ceramics. In this work, a new lead-free luminescent BLSF was fabricated by introducing Eu ions as the activator into SrBi2Nb2O9. The ferroelectric, piezoelectric, dielectric and photoluminescence
14850
L. Yu et al. / Ceramics International 42 (2016) 14849–14854
properties of Sr1 xEuxBi2Nb2O9 ceramics were investigated.
2. Experimental procedure Sr1-xEuxBi2Nb2O9 (SBT-xEu, x ¼0.000, 0.002, 0.004, 0.006) ceramics were prepared by a conventional solid-state reaction method. The high purity oxides and carbonates powders, SrCO3 (99%, Sinopharm Chemical Reagent), Bi2O3 (98%, Sinopharm Chemical Reagent), Nb2O5 (99.5%, Sinopharm Chemical Reagent) and Eu2O3 (99.99%, Sinopharm Chemical Reagent) were used as the raw materials, which had been treated carefully by a drying process. Then, all raw materials were weighted at stoichiometric proportion and wet milled in polyethylene bottles with ZrO2 balls for 15 h with 180 rounds per minute in alcohol. After drying, the mixed powders were calcined at 850 °C for 2 h. The calcined powders were milled again for 15 h with 180 rounds per minute. Next, the obtained dry powders were mixed with an appropriate amount of PVA (8 wt%) binder and then were pressed into 12 mm and 15 mm diameter, 0.3 mm and 1 mm thickness discs under a uniaxial pressure of 200 MPa. The 12 mm diameter and 0.3 mm thickness discs were used for the ferroelectric, piezoelectric and photoluminescence properties measurement, and the 15 mm diameter and 1 mm thickness discs was selected for the dielectric properties measurement. After burning off PVA at 550 °C, the samples were sintered in an alumina crucible at 1120 °C for 3 h in air. Finally, the sintered pellets were polished and covered with silver paste on both sides, then fired at 850 °C for 20 min. The crystalline structure of the crushed samples was analyzed by X-ray diffraction (XRD) methods (D8 Advanced, Bruker. Inc., Germany). The microstructure evolution was observed using a scanning electron microscope (SEM, JSM-6380LV, Tokyo, Japan). The ferroelectric hysteresis loops were measured through standardized ferroelectric test system (TF2000, Germany). The piezoelectric coefficient d33 was measured with a Piezo-d33 meter (Sznocera Piezotronics INC, China). The temperature dependence of dielectric properties for the samples was performed using a Broadband Dielectric Spectrometer (Novocontrol Germany) at temperatures ranging from room temperature to 700 °C with a heating rate of 3 °C/min. The photoluminescence (PL) spectra at RT were measured using aspectrofluorometer (FLS920, Edinburgh Instruments, UK).
3. Results and discussion Fig. 1 shows the XRD patterns of the SBN-xEu ceramics in the 2θ range of 20–70°. As shown, all the samples have been crystallized into a bismuth oxide layer-type structure without any traceable secondary phases. This implies that Eu3 þ have diffused into the crystal lattice of SBN and formed a stable solid solution with SBN. It also observed that the main diffraction peaks of all the samples in position and intensity change unobvious. This can be attributed to the similarity in ionic radii and electrical valence of Sr2 þ (1.44 Å, CN¼ 12) and Eu3 þ (1.23 Å, CN ¼12). In addition, the strongest diffraction peak is the (115) orientation, which corresponds well with the (112m þ1) highest diffraction peak in BLSFs. This indicates that all ceramics have the bismuth layer-structured compounds with the layer number m¼ 2. Fig. 2 shows the FE-SEM images of the nature surface for the pure and Eu3 þ -modified SBN ceramics sintered at 1120 °C for 3 h. It can be seen that the ceramics have a dense structure and platelike grains, which is the typical morphology feature of BLSF ceramics. Due to the grain is structurally high anisotropic, the grain growth is preferentially in the a-b plane perpendicular to the caxis of the BLSFs crystal, the lengthlof the plate-like grain is much
Fig. 1. The XRD pattems of the SBN-xEu (x ¼ 0.000–0.006) ceramics in the 2θ range of 20–70°.
bigger than the thickness t. Moreover, the grain size initially increases with the increasing Eu3 þ contents, and then decreases with the further increase of Eu3 þ contents. This implies that the appropriate content of Eu3 þ is beneficial to the grain growth of the ceramics. Kan et al. [15] and Hou et al. [16] both reported that grain growth during sintering is closely associated with ion migration. In the present work, the reduced grain growth rate can be linked with an increase in the activating energy for ion migration and reduction in the surface or grain boundary energy [16,17]. In addition, all ceramics have a high relative density (ρrd 490%, shown in Table 1), suggesting all samples have been well sintered. Fig. 3 shows the temperature dependence of the dielectric constant (εr) and dielectric loss (tanδ) for the SBN-xEu ceramics at 1 MHz. The values of Curie temperature and room temperature εr/ tanδ of the SBN-xEu ceramics are summarized in Table 1, the Curie temperatures (Tc), which corresponding to the ferroelectricparaelectric phase transition, changes slightly when the contents of the Eu3 þ is in the range of 0.000–0.004. When the Eu3 þ content reaches 0.006, the Curie temperatures (Tc) drop sharply. Shimakawa et al. [18,19] suggested that the Curie temperatures (Tc) depend strongly on the crystal structure distortion. The decrease of Tc at high Eu3 þ content may be related to the lattice distortion [18–20], the electronic configuration [21], the decrease of electronegativity (Sr2 þ :0.95, Eu3 þ :1.20) [22] and the Bi3 þ amounts [20,22,23]. The dielectric loss tangent (tanδ) of all samples are lower than 2% without significant conductivity appearing even at temperature as high as 400 °C, which suggest that the ceramics are suitable for high temperature applications. Moreover, it can be clearly seen that the loss tangent of the modified ceramics are lower than that of pure SBN, confirming the significantly improved insulation. For samples of SBT-0.002Eu, the tanδ is found to be only 0.96%. Fig. 4 shows the temperature dependence of the DC resistivity of the SBN-xEu ceramics measured in the temperature range of 500–700 °C, and the activation energy Ea values versus the content of Eu3 þ are listed in this graph. It is found that the resistivity increased with the increase of Eu3 þ content, but all the samples are higher than 104 Ω cm at 700 °C. In Aurivillius compounds, the structure built up by (Am 1BmO3m þ 1)2 layers and (Bi2O2)2 þ layers along c-axis [24]. The resistivity in the c-axis is higher than that in the a-b plane owing to the (Bi2O2)2 þ layers act as the insulating layer in the structure of Aurivillius compounds [25,26]. High resistivity is important for their use in high temperature piezoelectric devices, which is benefit to achieve high electric field poling at high temperature and get higher piezoelectric properties [27,28]. The activation energy (Ea) was calculated according to the
L. Yu et al. / Ceramics International 42 (2016) 14849–14854
14851
Fig. 2. The FE-SEM images of the SBN-xEu (x¼ 0.000–0.006) ceramics sintered at 1120 °C for 3 h.
Table 1 The electric properties of the SBN-xEu (x¼ 0.000–0.06) ceramics at room temperature. Composition (x) ρrd (%) εr
tanδ (%) Tc (°C) Ea (eV) 2Pr (μC/ cm2)
d33 Ec (kV/ (pC/ cm) N)
0.000 0.002 0.004 0.006
1.39 0.96 1.11 1.18
65 59 55 53
90.14 91.62 91.71 92.07
133 108 124 114
452 451 450 429
0.4833 0.4972 0.5012 0.5041
8.55 11.36 11.02 11.97
12 13 13 14
Fig. 4. Temperature dependence of the DC resistivity of the SBN-xEu (x ¼0.000– 0.006) ceramics.
A-site vacancies, as shown in Eq. (1).
Eu2O3
2SrO • → 2EuSr + V″Sr + 3OX o
(1) 2þ
Fig. 3. Temperature dependence of dielectric constant (εr) and dielectric loss (tanδ) for the SBN-xEu (x¼ 0.000–0.006) ceramics measured at 1 MHz.
Arrhenius relationship: ρ ¼ ρο exp(Ea/kBT), where kB is Boltzmann constant, ρο is the pre-exponential factor, Ea is activation energy and T is absolute temperature [27,29]. The activation energy (Ea) was determined to be in the range of 0.4833–0.5041 eV, indicating that the movement of oxygen vacancies is responsible for DC conduction process. Higher Ea in the Eu-modified samples can be explained by the fact that substitution of Eu3 þ into the Sr2 þ sites results in a reduction in oxygen vacancies. Eu3 þ (1.23 Å, CN¼ 12) occupies the A-sites of Sr2 þ (1.44 Å, CN ¼12) ions in the present study [14]. In this case, Eu3 þ acts as a donor leading to several
3þ
Partial substitution of bivalent Sr by trivalent Eu introduces extra oxygen ions that occupy available oxygen vacancies or create new Sr2 þ vacancies. Consequently, the number of charge carriers (i.e., number of oxygen vacancies) decreases and thus leads to the increase of Ea. Fig. 5 shows the ferroelectric hysteresis loops of the SBN-xEu ceramics recorded at 10 Hz and 180 °C under an external applied electric field of 170 kV/cm. Under such a high drive electric field, the hysteresis loops approach saturation. The remnant polarization (2Pr) increases with the increase of the Eu3 þ contents, while the coercive field (Ec) decreases slightly. This indicates that the ferroelectric properties are enhanced by Eu3 þ doping into SBN ceramics. When the doping content is 0.006, the 2Pr achieves a maximum value of 11.97 μC/cm2 with a relatively low coercive field of 53 kV/cm. The origin of the improvement in 2Pr of SBN-xEu is related to the domain switching behavior. The Eu3 þ substitution
14852
L. Yu et al. / Ceramics International 42 (2016) 14849–14854
Fig. 5. The P-E hysteresis loops of the SBN-xEu (x¼ 0.000–0.006) ceramics recorded at 10 Hz and 180 °C.
can increase the number of switchable domain under electric field, and thus a large number of domains contribute to the increase of 2Pr [30–32]. In addition, the 2Pr enhancement is also probably attributed to the structural distortion and decreased oxygen vacancies induced by the Eu3 þ modification. Generally, oxygen vacancies could accumulate near domain boundaries and cause domain pinning to reduce 2Pr [1,33,34]. While in the present work, the Eu3 þ have a small ion radius (r ¼1.23 Å, CN¼ 12) than the replaced Sr2 þ ion radius (r ¼ 1.44 Å, CN ¼12). Thus, the small ionic radius Eu3 þ substitution will increase the structural distortion of oxygen octahedral and then lead to the increase of 2Pr in the compound. Fig. 6(a) shows the piezoelectric constant d33 of the SBN-xEu ceramics poling at 180 °C for 20 min. Fig. 6(b) shows thermal annealing behavior for the Eu3 þ -modified SBN ceramics, in which the piezoelectric coefficients d33 are plotted against the annealing temperature. Obviously, the d33 value increases slightly as the Eu3 þ contents increases. The SBN-0.006Eu ceramics exhibit good piezoelectric performance (d33 ¼14 pC/N). In addition, the values of piezoelectric constant d33 of all the SBN ceramics show no obvious drop when the depolarization temperature is lower than 350 °C. It indicates that the ceramic has excellent temperature stability so that it is very tolerant to thermal annealing, and might be an appropriate candidate for high temperature piezoelectric applications [35]. With further increase of annealing temperature, the d33 of the SBN-xEu ceramics start to decrease sharply. Then, it tends to zero when the annealing temperature is above the Curie
Fig. 7. The PLE and PL spectra of the SBN-xEu (x ¼0.000–0.006) ceramics (λem ¼614 nm, λex ¼465 nm) at room temperature.
temperature. Fig. 7 shows the photoluminescence excitation spectra (PLE, monitored 614 nm) and the photoluminescence emission spectra (PL, under 465 nm) spectra of the SBN-xEu (x ¼0.002–0.006) ceramics sintered at 1120 °C for 3 h. As shown, the PLE spectrum consists of a strong peak at about 465 nm, which corresponds to the transition of 7F0-5D2. This implies that the SBN-xEu ceramics is suitable to be as near UV and blue light excited red phosphor. Under 465 nm light excitation, the major emission peaks are observed at 538, 593, 616, 653 and 699 nm, which is attributed to the radiative transition 5D1-7F1 and 5D0-7FJ (J ¼0–4), respectively. Among these peaks, the red emission peak centered at 616 nm corresponding to the electric dipole transition of 5D0-7F2 is more dominant than the other peaks. This indicates that Eu3 þ occupies a non-centro-symmetic site [9]. Fig. 8(a) shows photoluminescence emission spectra of the SBN-xEu ceramics under 465 nm light excitation at room temperature. The energy level diagram for Eu3 þ ion is shown in Fig. 8 (b). Clearly, the emission peak position has no difference with the increase of Eu3 þ ion concentration, while the emission intensity changes drastically with the increase of Eu3 þ ion concentration. At x¼ 0.004, the PL intensity reaches a maximum value, then it decreases remarkably due to the concentration quenching effect [30]. Jiang et al. [36] reported that the concentration quenching effect existed in the bismuth layer perovskite structure. The Eu3 þ ions preferentially enter the (Am 1BmO3m þ 1)2 layers, which primarily
Fig. 6. (a) The piezoelectric constant d33 of the SBN-xEu (x ¼0.000–0.006) ceramics poling at 180 °C for 20 min (b) Thermal annealing behavior for the Eu3 þ -modified SBN ceramics.
L. Yu et al. / Ceramics International 42 (2016) 14849–14854
14853
Fig. 8. (a) The optical property of the SBN-xEu (x ¼0.000–0.006) ceramics, (b) The energy level diagram of the red emissions for the Eu-modified SBN ceramics.
occurred the energy transfer, rather than in (Bi2O2)2 þ layers [36]. Thus, nonradiative energy transfer between nearby Eu3 þ ions exceeds the critical value. This leads to the high quenching concentrations and the luminescence intensity decrease [9,36]. Under 465 nm excitation, the major emission peaks are observed in the range of 530–700 nm, corresponds to a weak green 5D1-7F1 transition and the characteristic emission bands (5D0-7FJ, J ¼1–4). Among these peaks, ta red emission centered at 616 nm corresponding to an electric dipole transition of 5D0-7F2 is outstanding, which is hypersensitive to the symmetry of the RE3 þ in the host lattice [13]. Furthermore, the yellow emission centered at 593 nm, attributes to the 5D0-7F1 transition, a magnetic dipole transition, which is independent of surroundings of the Eu3 þ in the matrix [13].
4. Conclusion In summary, Sr1 xEuxBi2Nb2O9 compounds specimens were prepared by a conventional solid-state reaction method. The photoluminescence properties of the ceramics were investigated, and the SBN-0.004Eu ceramic showed the strongest emissions. Under 465 nm light excitation, the major emission peaks are observed at 538, 593, 616, 653 and 699 nm, which attributed to a weak green 5D1-7F1 transition and the characteristic emission bands (5D0-7FJ, J ¼1–4). The red emission centered at 616 nm, corresponds to an electric dipole transition of 5D0-7F2, and the yellow emission centered at 593 nm, attributes to a magnetic dipole transition of 5D0-7F1. Simultaneously, the enhanced ferroelectric, piezoelectric and dielectric properties were obtained by Eu3 þ doping. The SBN-0.006Eu samples exhibit good piezoelectric (d33 ¼14 pC/N) and ferroelectric (2Pr ¼11.97 μC/cm2) properties, together with a high resistivity, high activation energy (Ea ¼0.5041 eV) and good thermal stabilities. As a multifunctional material, the SBN-xEu ceramics may be promising materials in novel multifunctional optoelectronic devices and high temperature piezoelectric sensors applications.
Acknowledgments This work was supported by the National Natural Science Foundation of China, China (Nos. 51402144, 51372110, 51502127 and 51302124), the Project of Shandong Province Higher Educational Science and Technology Program (Grant Nos. J14LA11 and J14LA10), Science and Technology Planning Project of Guangdong Province, China (No. 2013B091000001), Independent Innovation
and Achievement Transformation in Shandong Province Special, China (No. 2014CGZH0904), the Natural Science Foundation of Shandong Province of China, China (Grant no. ZR2014JL030), and the Research Foundation of Liaocheng University (No. 318011306).
References [1] C. Diao, H. Li, Z. Chen, H. Zheng, Effect of samarium substitution on the dielectric and ferroelectric properties of BaBi4 xSmxTi4O15 ceramics, Ceram. Int. 42 (2016) 621–626. [2] S. Zhang, F. Yu, D.J. Green, Piezoelectric materials for high temperature sensors, J. Am. Ceram. Soc. 94 (2011) 3153–3170. [3] J. Xiao, H. Zhang, Y. Xue, Z. Lu, X. Chen, P. Su, F. Yang, X. Zeng, The influence of Ni-doping concentration on multiferroic behaviors in Bi4NdTi3FeO15 ceramics, Ceram. Int. 41 (2015) 1087–1092. [4] M.-L. Zhao, Q.-Z. Wu, C.-L. Wang, J.-L. Zhang, Z.-G. Gai, C.-M. Wang, Dielectric and piezoelectric properties of Na0.5Bi4.5Ti4O15–(x 1)Na0.5Bi0.5TiO3 composite ceramics, J. Alloy. Compd. 476 (2009) 393–396. [5] J. Zhu, X.-B. Chen, J.-h He, J.-C. Shen, Investigations on Raman and X-ray photoemission scattering patterns of vanadium-doped SrBi4Ti4O15 ferroelectric ceramics, Phys. Lett. A 362 (2007) 471–475. [6] Y. Tang, Z.-y Shen, S. Zhang, T.R. Shrout, A. Feteira, Improved pyroelectric properties of CaBi4Ti4O15 ferroelectrics ceramics by Nb/Mn Co-doping for pyrosensors, J. Am. Ceram. Soc. 99 (2016) 1294–1298. [7] C.-M. Wang, J.-F. Wang, C. Mao, X. Chen, X. Dong, Z.-G. Gai, M.-L. Zhao, Enhanced dielectric and piezoelectric properties of aurivillius-type potassium bismuth titanate ceramics by cerium modification, J. Am. Ceram. Soc. 91 (2008) 3094–3097. [8] D. Peng, H. Sun, X. Wang, J. Zhang, M. Tang, X. Yao, Blue excited photoluminescence of Pr doped CaBi2Ta2O9 based ferroelectrics, J. Alloy. Compd. 511 (2012) 159–162. [9] R. Cui, C. Deng, X. Gong, X. Li, J. Zhou, Luminescent performance of rare earths doped CaBi2Ta2O9 phosphor, J. Rare Earth 31 (2013) 546–550. [10] K. Ruan, X. Chen, T. Liang, G. Wu, D. Bao, Improved photoluminescence and electrical properties of Eu- and Gd-codoped bismuth titanate ferroelectric thin films, J. Appl. Phys. 103 (2008) 086104. [11] H. Sun, D. Peng, X. Wang, M. Tang, Q. Zhang, X. Yao, Strong red emission in Pr doped (Bi0.5Na0.5)TiO3 ferroelectric ceramics, J. Appl. Phys. 110 (2011) 016102. [12] Z. Yao, H. Li, M. Ma, R. Chu, Z. Xu, J. Hao, G. Li, Preparation and electrical properties of (1 x)SrBi2Nb2O9 xBiFeO3 lead-free piezoelectric ceramics, Ceram. Int. 42 (2016) 5391–5396. [13] W. Xie, L. Su, T. Sa, J. Fu, W. Hu, N. Qin, D. Bao, Strong red emission and electrical properties of highly c-axis oriented Eu3 þ -doped bismuth vanadate ferroelectric thin films, Mater. Chem. Phys. 148 (2014) 854–858. [14] R.-R. Cui, C.-Y. Deng, X.-Y. Gong, X.-C. Li, J.-P. Zhou, Luminescence properties of Eu3 þ doped CaBi2Ta2O9 bismuth layered-structure ferroelectrics, Mater. Res. Bull. 48 (2013) 4301–4306. [15] Y.-M. Kan, G.-J. Zhang, P.-L. Wang, Y.-B. Cheng, Preparation and properties of neodymium-modified bismuth titanate ceramics, J. Eur. Ceram. Soc. 28 (2008) 1641–1647. [16] J. Hou, R.V. Kumar, Y. Qu, D. Krsmanovic, B-site doping effect on electrical properties of Bi4Ti3 2xNbxTaxO12 ceramics, Scr. Mater. 61 (2009) 664–667. [17] X.-P. Jiang, X.-L. Fu, C. Chen, N. Tu, M.-Z. Xu, X.-H. Li, H. Shao, Y.-J. Chen, High performance Aurivillius type Na0.5Bi4.5Ti4O15 piezoelectric ceramics with neodymium and cerium modification, J. Adv. Ceram. 4 (2015) 54–60. [18] Y. Shimakawa, Y. Kubo, Y. Nakagawa, T. Kamiyama, H. Asano, F. Izumi, Crystal structures and ferroelectric properties of SrBi2Ta2O9 and Sr0.8Bi2.2Ta2O9, Appl. Phys. Lett. 74 (1999) 1904.
14854
L. Yu et al. / Ceramics International 42 (2016) 14849–14854
[19] Y. Shimakawa, Y. Kubo, Y. Tauchi, T. Kamiyama, H. Asano, F. Izumi, Structural distortion and ferroelectric properties of SrBi2(Ta1 xNbx)2O9, Appl. Phys. Lett. 77 (2000). [20] E. Subbarao, Crystal chemistry of mixed bismuth oxides with layer-type structure, J. Am. Ceram. Soc. 45 (1962) 166–169. [21] T. Sivakumar, M. Itoh, Ferroelectric phase transitions in new Aurivillius oxides: Bi22xþ Sr1 2xNb2 xScxO9, J. Mater. Chem. 21 (2011) 10865–10870. [22] J. Mercurio, A. Souirti, M. Manier, B. Frit, Phase transitions and dielectric properties in some compounds with bismuth oxide layer structure, Mater. Res. Bull. 27 (1992) 123–128. [23] X.-P. Jiang, X.-L. Fu, C. Chen, N. Tu, M.-Z. Xu, X.-H. Li, H. Shao, Y.-J. Chen, High performance Aurivillius type Na0.5Bi4.5Ti4O15 piezoelectric ceramics with neodymium and cerium modification,, J. Adv. Ceram 4 (2015) 54–60. [24] Y. Wu, M.J. Forbess, S. Seraji, S.J. Limmer, T.P. Chou, C. Nguyen, G. Cao, Doping effect in layer structured SrBi2Nb2O9 ferroelectrics, J. Appl. Phys. 90 (2001) 5296. [25] Z.-Y. Zhou, X.-L. Dong, H.-X. Yan, Lanthanum distribution and dielectric properties of Bi3 xLaxTiNbO9 bismuth layer-structured ceramics, Scr. Mater. 55 (2006) 791–794. [26] H. Chen, B. Shen, J. Xu, J. Zhai, Textured Ca0.85(Li,Ce)0.15Bi4Ti4O15 ceramics for high temperature piezoelectric applications, Mater. Res. Bull. 47 (2012) 2530–2534. [27] P. Fang, P. Liu, Z. Xi, W. Long, X. Li, Structure and electrical properties of new Aurivillius oxides (K0.16Na0.84)0.5Bi4.5Ti4O15 with manganese modification, J. Alloy. Compd. 595 (2014) 148–152.
[28] H. Yan, Z. Zhang, W. Zhu, L. He, Y. Yu, C. Li, J. Zhou, The effect of (Li,Ce) and (K, Ce) doping in Aurivillius phase material CaBi4Ti4O15, Mater. Res. Bull. 39 (2004) 1237–1246. [29] Z. Peng, Y. Chen, Q. Chen, N. Li, X. Zhao, C. Kou, D. Xiao, J. Zhu, Correlation between lattice distortion and electrical properties on Bi4Ti3O12 ceramics with W/Ni modifications, J. Alloy. Compd. 590 (2014) 210–214. [30] D. Peng, H. Sun, X. Wang, J. Zhang, M. Tang, X. Yao, Red emission in Pr doped CaBi4Ti4O15 ferroelectric ceramics, Mater. Sci. Eng. B 176 (2011) 1513–1516. [31] U. Chon, J.S. Shim, H.M. Jang, Ferroelectric properties and crystal structure of praseodymium-modified bismuth titanate, J. Appl. Phys. 93 (2003) 4769. [32] Y. Noguchi, A. Kitamura, L.-C. Woo, M. Miyayama, K. Oikawa, T. Kamiyama, Praseodymium-modified SrBi2Ta2O9 with improved polarization properties at low electric field, J. Appl. Phys. 94 (2003) 6749–6752. [33] Y. Shimakawa, Y. Kubo, Y. Nakagawa, S. Goto, T. Kamiyama, H. Asano, F. Izumi, Crystal structure and ferroelectric properties of ABi2Ta2O9 (A ¼Ca, Sr, and Ba), Phys. Rev. B 61 (2000) 6559. [34] Y. Zhao, H. Fan, G. Liu, Z. Liu, X. Ren, Ferroelectric, piezoelectric properties and magnetoelectric coupling behavior in aurivillius Bi5Ti3FeO15 multiferroic nanofibers by electrospinning, J. Alloy. Compd. 675 (2016) 441–447. [35] Z. Yao, R. Chu, Z. Xu, J. Hao, G. Li, Enhanced electrical properties of (Li,Ce) codoped Sr(Na0.5Bi0.5)Bi4Ti5O18 high temperature piezoceramics, RSC Adv. 6 (40) (2016) 33387–33392. [36] X. Jiang, X. Jiang, C. Chen, N. Tu, Y. Chen, B. Zhang, Photoluminescence and electrical properties of Eu3 þ -doped Na0.5Bi4.5Ti4O15-based ferroelectrics under blue light excitation, Front. Mater. Sci. 10 (2015) 31–37.
Contents lists available at ScienceDirect
Ceramics International journal homepage: www.elsevier.com/locate/ceramint
Strong photoluminescence and good electrical properties in Eumodified SrBi2Nb2O9 multifunctional ceramics Lei Yu a, Jigong Hao a,n, Zhijun Xu a, Wei Li a, Ruiqing Chu a,n, Guorong Li b a
College of Materials Science and Engineering, Liaocheng University, Liaocheng 252059, People's Republic of China The State Key Lab of High Performance Ceramics and Superfinemicrostructure, Shanghai Institute of Ceramics, Chinese Academy of Science, Shanghai 200050, People’s Republic of China b
art ic l e i nf o
a b s t r a c t
Article history: Received 1 June 2016 Received in revised form 17 June 2016 Accepted 19 June 2016 Available online 23 June 2016
Bismuth layer-structured ferroelectric (BLSFs) ceramics of Sr1 xEux Bi2Nb2O9 (SBT-xEu, x ¼0.000, 0.002, 0.004, 0.006) were prepared by a conventional solid-state reaction method. All the samples have a bismuth oxide layered structure with a dense microstructure. The ferroelectric, piezoelectric, dielectric and optical properties of the ceramics were investigated. After Eu3 þ doping, samples show a bright red photoluminescence upon blue light excitation of the 400–500 nm. Upon the excitation of 465 nm light, the materials have two intense emission bands peaking around 593 nm (yellow) and 616 nm (red). Meanwhile, good electrical properties with large piezoelectric constant d33 of 14 pC/N and large remnant polarization 2Pr of 11.97 μC/cm2 are obtained at x ¼ 0.006. Moreover, this material has a high Curie temperature (Tc ¼ 429 °C) and high resistivity, which makes the material resistant to thermal depolarization up to its Curie temperature. This feature indicates that the SBN-xEu ceramics have a latent use in high temperature applications. & 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Keywords: Bismuth layer-structured ferroelectric Photoluminescence Excitation Red emission Curie temperature
1. Introduction Aurivillius bismuth-layer structure ferroelectrics (BLSFs) have received significant attention for the latent use in high-temperature sensors, non-volatile random access memory (NVRAM) and piezoelectric resonators due to their high Curie temperature, low dielectric constant, low aging rate and anisotropic electromechanical coupling factors [1,2]. BLSFs compounds have the general formula (Bi2O2)2 þ (Am 1BmO3m þ 1)2–, where A is a mono-, di- or tri-valent ions (or their combination) such as Sr2 þ , Ca2 þ etc, B is tetra-, penta-, or hexa-valent ions (or their combination) with appropriate size such as Ti4 þ , Nb5 þ etc, and m is number of pseudo-perovskite (Am 1BmO3m þ 1)2– layers which varies from 1 to 5 [3–5]. The crystal structure of BLSF can be described as perovskite-like (Am 1BmO3m þ 1)2 layers interleaved with bismuth oxide (Bi2O2)2 þ layers units along the c-axes [6,7]. While the perovskite-like layers offer large possibilities in terms of compositional flexibility, it could incorporate various cations such as Na þ , K þ , Ca2 þ , Sr2 þ , Ba2 þ for the A-site and Ti4 þ , Nb5 þ , W6 þ for the B-site. The cation sites in the interleave (Bi2O2)2 þ layers are almost exclusively occupied by Bi3 þ cations forming (Bi2O2)2 þ slabs. Some cations, include the above mentioned cations and the n
Corresponding authors. E-mail addresses: [email protected] (J. Hao), [email protected] (R. Chu).
http://dx.doi.org/10.1016/j.ceramint.2016.06.119 0272-8842/& 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
rare earth ions (RE3 þ , such as Er3 þ , Eu3 þ , Ho3 þ , Pr3 þ etc), could improve the properties of the BLSFs. The RE3 þ ions are always regarded as the luminous centers to design a large number of luminescent materials due to their special electronic structure [8]. Owing to the luminescent behavior of RE3 þ , BLSFs modified by RE3 þ show novel photoluminescence properties besides retaining the ferroelectric functions [9]. In addition, the Bi3 þ ion can function as both an activator and a sensitizer to develop phosphors for the photoluminescence materials [10,11]. Along with the intensive development of microelectronic devices toward multiple functions, it is of interest and significance to study the potential luminescent properties of RE3 þ doped BLSFs for multifunctional material applications. SrBi2Nb2O9 (SBN) ceramics have a typical layer-structured ferroelectrics (m ¼2). Yao et al. [12] reported that the SBN sample shows a high Curie temperature (444 °C), low dielectric loss tanδ (1.47%) and temperature-insensitive large piezoelectric coefficient. This material is believed to be a very promising candidate for high temperature applications. Additionally, it was found that the Eu3 þ ion exhibited bright red emission at room temperature upon blue light excitation of the 400–500 nm [13]. The Eu3 þ ion occupy the A-site (Sr2 þ ) of SrBi2Nb2O9 ceramic [14], which may be very helpful to improve the performance of the SBN ceramics. In this work, a new lead-free luminescent BLSF was fabricated by introducing Eu ions as the activator into SrBi2Nb2O9. The ferroelectric, piezoelectric, dielectric and photoluminescence
14850
L. Yu et al. / Ceramics International 42 (2016) 14849–14854
properties of Sr1 xEuxBi2Nb2O9 ceramics were investigated.
2. Experimental procedure Sr1-xEuxBi2Nb2O9 (SBT-xEu, x ¼0.000, 0.002, 0.004, 0.006) ceramics were prepared by a conventional solid-state reaction method. The high purity oxides and carbonates powders, SrCO3 (99%, Sinopharm Chemical Reagent), Bi2O3 (98%, Sinopharm Chemical Reagent), Nb2O5 (99.5%, Sinopharm Chemical Reagent) and Eu2O3 (99.99%, Sinopharm Chemical Reagent) were used as the raw materials, which had been treated carefully by a drying process. Then, all raw materials were weighted at stoichiometric proportion and wet milled in polyethylene bottles with ZrO2 balls for 15 h with 180 rounds per minute in alcohol. After drying, the mixed powders were calcined at 850 °C for 2 h. The calcined powders were milled again for 15 h with 180 rounds per minute. Next, the obtained dry powders were mixed with an appropriate amount of PVA (8 wt%) binder and then were pressed into 12 mm and 15 mm diameter, 0.3 mm and 1 mm thickness discs under a uniaxial pressure of 200 MPa. The 12 mm diameter and 0.3 mm thickness discs were used for the ferroelectric, piezoelectric and photoluminescence properties measurement, and the 15 mm diameter and 1 mm thickness discs was selected for the dielectric properties measurement. After burning off PVA at 550 °C, the samples were sintered in an alumina crucible at 1120 °C for 3 h in air. Finally, the sintered pellets were polished and covered with silver paste on both sides, then fired at 850 °C for 20 min. The crystalline structure of the crushed samples was analyzed by X-ray diffraction (XRD) methods (D8 Advanced, Bruker. Inc., Germany). The microstructure evolution was observed using a scanning electron microscope (SEM, JSM-6380LV, Tokyo, Japan). The ferroelectric hysteresis loops were measured through standardized ferroelectric test system (TF2000, Germany). The piezoelectric coefficient d33 was measured with a Piezo-d33 meter (Sznocera Piezotronics INC, China). The temperature dependence of dielectric properties for the samples was performed using a Broadband Dielectric Spectrometer (Novocontrol Germany) at temperatures ranging from room temperature to 700 °C with a heating rate of 3 °C/min. The photoluminescence (PL) spectra at RT were measured using aspectrofluorometer (FLS920, Edinburgh Instruments, UK).
3. Results and discussion Fig. 1 shows the XRD patterns of the SBN-xEu ceramics in the 2θ range of 20–70°. As shown, all the samples have been crystallized into a bismuth oxide layer-type structure without any traceable secondary phases. This implies that Eu3 þ have diffused into the crystal lattice of SBN and formed a stable solid solution with SBN. It also observed that the main diffraction peaks of all the samples in position and intensity change unobvious. This can be attributed to the similarity in ionic radii and electrical valence of Sr2 þ (1.44 Å, CN¼ 12) and Eu3 þ (1.23 Å, CN ¼12). In addition, the strongest diffraction peak is the (115) orientation, which corresponds well with the (112m þ1) highest diffraction peak in BLSFs. This indicates that all ceramics have the bismuth layer-structured compounds with the layer number m¼ 2. Fig. 2 shows the FE-SEM images of the nature surface for the pure and Eu3 þ -modified SBN ceramics sintered at 1120 °C for 3 h. It can be seen that the ceramics have a dense structure and platelike grains, which is the typical morphology feature of BLSF ceramics. Due to the grain is structurally high anisotropic, the grain growth is preferentially in the a-b plane perpendicular to the caxis of the BLSFs crystal, the lengthlof the plate-like grain is much
Fig. 1. The XRD pattems of the SBN-xEu (x ¼ 0.000–0.006) ceramics in the 2θ range of 20–70°.
bigger than the thickness t. Moreover, the grain size initially increases with the increasing Eu3 þ contents, and then decreases with the further increase of Eu3 þ contents. This implies that the appropriate content of Eu3 þ is beneficial to the grain growth of the ceramics. Kan et al. [15] and Hou et al. [16] both reported that grain growth during sintering is closely associated with ion migration. In the present work, the reduced grain growth rate can be linked with an increase in the activating energy for ion migration and reduction in the surface or grain boundary energy [16,17]. In addition, all ceramics have a high relative density (ρrd 490%, shown in Table 1), suggesting all samples have been well sintered. Fig. 3 shows the temperature dependence of the dielectric constant (εr) and dielectric loss (tanδ) for the SBN-xEu ceramics at 1 MHz. The values of Curie temperature and room temperature εr/ tanδ of the SBN-xEu ceramics are summarized in Table 1, the Curie temperatures (Tc), which corresponding to the ferroelectricparaelectric phase transition, changes slightly when the contents of the Eu3 þ is in the range of 0.000–0.004. When the Eu3 þ content reaches 0.006, the Curie temperatures (Tc) drop sharply. Shimakawa et al. [18,19] suggested that the Curie temperatures (Tc) depend strongly on the crystal structure distortion. The decrease of Tc at high Eu3 þ content may be related to the lattice distortion [18–20], the electronic configuration [21], the decrease of electronegativity (Sr2 þ :0.95, Eu3 þ :1.20) [22] and the Bi3 þ amounts [20,22,23]. The dielectric loss tangent (tanδ) of all samples are lower than 2% without significant conductivity appearing even at temperature as high as 400 °C, which suggest that the ceramics are suitable for high temperature applications. Moreover, it can be clearly seen that the loss tangent of the modified ceramics are lower than that of pure SBN, confirming the significantly improved insulation. For samples of SBT-0.002Eu, the tanδ is found to be only 0.96%. Fig. 4 shows the temperature dependence of the DC resistivity of the SBN-xEu ceramics measured in the temperature range of 500–700 °C, and the activation energy Ea values versus the content of Eu3 þ are listed in this graph. It is found that the resistivity increased with the increase of Eu3 þ content, but all the samples are higher than 104 Ω cm at 700 °C. In Aurivillius compounds, the structure built up by (Am 1BmO3m þ 1)2 layers and (Bi2O2)2 þ layers along c-axis [24]. The resistivity in the c-axis is higher than that in the a-b plane owing to the (Bi2O2)2 þ layers act as the insulating layer in the structure of Aurivillius compounds [25,26]. High resistivity is important for their use in high temperature piezoelectric devices, which is benefit to achieve high electric field poling at high temperature and get higher piezoelectric properties [27,28]. The activation energy (Ea) was calculated according to the
L. Yu et al. / Ceramics International 42 (2016) 14849–14854
14851
Fig. 2. The FE-SEM images of the SBN-xEu (x¼ 0.000–0.006) ceramics sintered at 1120 °C for 3 h.
Table 1 The electric properties of the SBN-xEu (x¼ 0.000–0.06) ceramics at room temperature. Composition (x) ρrd (%) εr
tanδ (%) Tc (°C) Ea (eV) 2Pr (μC/ cm2)
d33 Ec (kV/ (pC/ cm) N)
0.000 0.002 0.004 0.006
1.39 0.96 1.11 1.18
65 59 55 53
90.14 91.62 91.71 92.07
133 108 124 114
452 451 450 429
0.4833 0.4972 0.5012 0.5041
8.55 11.36 11.02 11.97
12 13 13 14
Fig. 4. Temperature dependence of the DC resistivity of the SBN-xEu (x ¼0.000– 0.006) ceramics.
A-site vacancies, as shown in Eq. (1).
Eu2O3
2SrO • → 2EuSr + V″Sr + 3OX o
(1) 2þ
Fig. 3. Temperature dependence of dielectric constant (εr) and dielectric loss (tanδ) for the SBN-xEu (x¼ 0.000–0.006) ceramics measured at 1 MHz.
Arrhenius relationship: ρ ¼ ρο exp(Ea/kBT), where kB is Boltzmann constant, ρο is the pre-exponential factor, Ea is activation energy and T is absolute temperature [27,29]. The activation energy (Ea) was determined to be in the range of 0.4833–0.5041 eV, indicating that the movement of oxygen vacancies is responsible for DC conduction process. Higher Ea in the Eu-modified samples can be explained by the fact that substitution of Eu3 þ into the Sr2 þ sites results in a reduction in oxygen vacancies. Eu3 þ (1.23 Å, CN¼ 12) occupies the A-sites of Sr2 þ (1.44 Å, CN ¼12) ions in the present study [14]. In this case, Eu3 þ acts as a donor leading to several
3þ
Partial substitution of bivalent Sr by trivalent Eu introduces extra oxygen ions that occupy available oxygen vacancies or create new Sr2 þ vacancies. Consequently, the number of charge carriers (i.e., number of oxygen vacancies) decreases and thus leads to the increase of Ea. Fig. 5 shows the ferroelectric hysteresis loops of the SBN-xEu ceramics recorded at 10 Hz and 180 °C under an external applied electric field of 170 kV/cm. Under such a high drive electric field, the hysteresis loops approach saturation. The remnant polarization (2Pr) increases with the increase of the Eu3 þ contents, while the coercive field (Ec) decreases slightly. This indicates that the ferroelectric properties are enhanced by Eu3 þ doping into SBN ceramics. When the doping content is 0.006, the 2Pr achieves a maximum value of 11.97 μC/cm2 with a relatively low coercive field of 53 kV/cm. The origin of the improvement in 2Pr of SBN-xEu is related to the domain switching behavior. The Eu3 þ substitution
14852
L. Yu et al. / Ceramics International 42 (2016) 14849–14854
Fig. 5. The P-E hysteresis loops of the SBN-xEu (x¼ 0.000–0.006) ceramics recorded at 10 Hz and 180 °C.
can increase the number of switchable domain under electric field, and thus a large number of domains contribute to the increase of 2Pr [30–32]. In addition, the 2Pr enhancement is also probably attributed to the structural distortion and decreased oxygen vacancies induced by the Eu3 þ modification. Generally, oxygen vacancies could accumulate near domain boundaries and cause domain pinning to reduce 2Pr [1,33,34]. While in the present work, the Eu3 þ have a small ion radius (r ¼1.23 Å, CN¼ 12) than the replaced Sr2 þ ion radius (r ¼ 1.44 Å, CN ¼12). Thus, the small ionic radius Eu3 þ substitution will increase the structural distortion of oxygen octahedral and then lead to the increase of 2Pr in the compound. Fig. 6(a) shows the piezoelectric constant d33 of the SBN-xEu ceramics poling at 180 °C for 20 min. Fig. 6(b) shows thermal annealing behavior for the Eu3 þ -modified SBN ceramics, in which the piezoelectric coefficients d33 are plotted against the annealing temperature. Obviously, the d33 value increases slightly as the Eu3 þ contents increases. The SBN-0.006Eu ceramics exhibit good piezoelectric performance (d33 ¼14 pC/N). In addition, the values of piezoelectric constant d33 of all the SBN ceramics show no obvious drop when the depolarization temperature is lower than 350 °C. It indicates that the ceramic has excellent temperature stability so that it is very tolerant to thermal annealing, and might be an appropriate candidate for high temperature piezoelectric applications [35]. With further increase of annealing temperature, the d33 of the SBN-xEu ceramics start to decrease sharply. Then, it tends to zero when the annealing temperature is above the Curie
Fig. 7. The PLE and PL spectra of the SBN-xEu (x ¼0.000–0.006) ceramics (λem ¼614 nm, λex ¼465 nm) at room temperature.
temperature. Fig. 7 shows the photoluminescence excitation spectra (PLE, monitored 614 nm) and the photoluminescence emission spectra (PL, under 465 nm) spectra of the SBN-xEu (x ¼0.002–0.006) ceramics sintered at 1120 °C for 3 h. As shown, the PLE spectrum consists of a strong peak at about 465 nm, which corresponds to the transition of 7F0-5D2. This implies that the SBN-xEu ceramics is suitable to be as near UV and blue light excited red phosphor. Under 465 nm light excitation, the major emission peaks are observed at 538, 593, 616, 653 and 699 nm, which is attributed to the radiative transition 5D1-7F1 and 5D0-7FJ (J ¼0–4), respectively. Among these peaks, the red emission peak centered at 616 nm corresponding to the electric dipole transition of 5D0-7F2 is more dominant than the other peaks. This indicates that Eu3 þ occupies a non-centro-symmetic site [9]. Fig. 8(a) shows photoluminescence emission spectra of the SBN-xEu ceramics under 465 nm light excitation at room temperature. The energy level diagram for Eu3 þ ion is shown in Fig. 8 (b). Clearly, the emission peak position has no difference with the increase of Eu3 þ ion concentration, while the emission intensity changes drastically with the increase of Eu3 þ ion concentration. At x¼ 0.004, the PL intensity reaches a maximum value, then it decreases remarkably due to the concentration quenching effect [30]. Jiang et al. [36] reported that the concentration quenching effect existed in the bismuth layer perovskite structure. The Eu3 þ ions preferentially enter the (Am 1BmO3m þ 1)2 layers, which primarily
Fig. 6. (a) The piezoelectric constant d33 of the SBN-xEu (x ¼0.000–0.006) ceramics poling at 180 °C for 20 min (b) Thermal annealing behavior for the Eu3 þ -modified SBN ceramics.
L. Yu et al. / Ceramics International 42 (2016) 14849–14854
14853
Fig. 8. (a) The optical property of the SBN-xEu (x ¼0.000–0.006) ceramics, (b) The energy level diagram of the red emissions for the Eu-modified SBN ceramics.
occurred the energy transfer, rather than in (Bi2O2)2 þ layers [36]. Thus, nonradiative energy transfer between nearby Eu3 þ ions exceeds the critical value. This leads to the high quenching concentrations and the luminescence intensity decrease [9,36]. Under 465 nm excitation, the major emission peaks are observed in the range of 530–700 nm, corresponds to a weak green 5D1-7F1 transition and the characteristic emission bands (5D0-7FJ, J ¼1–4). Among these peaks, ta red emission centered at 616 nm corresponding to an electric dipole transition of 5D0-7F2 is outstanding, which is hypersensitive to the symmetry of the RE3 þ in the host lattice [13]. Furthermore, the yellow emission centered at 593 nm, attributes to the 5D0-7F1 transition, a magnetic dipole transition, which is independent of surroundings of the Eu3 þ in the matrix [13].
4. Conclusion In summary, Sr1 xEuxBi2Nb2O9 compounds specimens were prepared by a conventional solid-state reaction method. The photoluminescence properties of the ceramics were investigated, and the SBN-0.004Eu ceramic showed the strongest emissions. Under 465 nm light excitation, the major emission peaks are observed at 538, 593, 616, 653 and 699 nm, which attributed to a weak green 5D1-7F1 transition and the characteristic emission bands (5D0-7FJ, J ¼1–4). The red emission centered at 616 nm, corresponds to an electric dipole transition of 5D0-7F2, and the yellow emission centered at 593 nm, attributes to a magnetic dipole transition of 5D0-7F1. Simultaneously, the enhanced ferroelectric, piezoelectric and dielectric properties were obtained by Eu3 þ doping. The SBN-0.006Eu samples exhibit good piezoelectric (d33 ¼14 pC/N) and ferroelectric (2Pr ¼11.97 μC/cm2) properties, together with a high resistivity, high activation energy (Ea ¼0.5041 eV) and good thermal stabilities. As a multifunctional material, the SBN-xEu ceramics may be promising materials in novel multifunctional optoelectronic devices and high temperature piezoelectric sensors applications.
Acknowledgments This work was supported by the National Natural Science Foundation of China, China (Nos. 51402144, 51372110, 51502127 and 51302124), the Project of Shandong Province Higher Educational Science and Technology Program (Grant Nos. J14LA11 and J14LA10), Science and Technology Planning Project of Guangdong Province, China (No. 2013B091000001), Independent Innovation
and Achievement Transformation in Shandong Province Special, China (No. 2014CGZH0904), the Natural Science Foundation of Shandong Province of China, China (Grant no. ZR2014JL030), and the Research Foundation of Liaocheng University (No. 318011306).
References [1] C. Diao, H. Li, Z. Chen, H. Zheng, Effect of samarium substitution on the dielectric and ferroelectric properties of BaBi4 xSmxTi4O15 ceramics, Ceram. Int. 42 (2016) 621–626. [2] S. Zhang, F. Yu, D.J. Green, Piezoelectric materials for high temperature sensors, J. Am. Ceram. Soc. 94 (2011) 3153–3170. [3] J. Xiao, H. Zhang, Y. Xue, Z. Lu, X. Chen, P. Su, F. Yang, X. Zeng, The influence of Ni-doping concentration on multiferroic behaviors in Bi4NdTi3FeO15 ceramics, Ceram. Int. 41 (2015) 1087–1092. [4] M.-L. Zhao, Q.-Z. Wu, C.-L. Wang, J.-L. Zhang, Z.-G. Gai, C.-M. Wang, Dielectric and piezoelectric properties of Na0.5Bi4.5Ti4O15–(x 1)Na0.5Bi0.5TiO3 composite ceramics, J. Alloy. Compd. 476 (2009) 393–396. [5] J. Zhu, X.-B. Chen, J.-h He, J.-C. Shen, Investigations on Raman and X-ray photoemission scattering patterns of vanadium-doped SrBi4Ti4O15 ferroelectric ceramics, Phys. Lett. A 362 (2007) 471–475. [6] Y. Tang, Z.-y Shen, S. Zhang, T.R. Shrout, A. Feteira, Improved pyroelectric properties of CaBi4Ti4O15 ferroelectrics ceramics by Nb/Mn Co-doping for pyrosensors, J. Am. Ceram. Soc. 99 (2016) 1294–1298. [7] C.-M. Wang, J.-F. Wang, C. Mao, X. Chen, X. Dong, Z.-G. Gai, M.-L. Zhao, Enhanced dielectric and piezoelectric properties of aurivillius-type potassium bismuth titanate ceramics by cerium modification, J. Am. Ceram. Soc. 91 (2008) 3094–3097. [8] D. Peng, H. Sun, X. Wang, J. Zhang, M. Tang, X. Yao, Blue excited photoluminescence of Pr doped CaBi2Ta2O9 based ferroelectrics, J. Alloy. Compd. 511 (2012) 159–162. [9] R. Cui, C. Deng, X. Gong, X. Li, J. Zhou, Luminescent performance of rare earths doped CaBi2Ta2O9 phosphor, J. Rare Earth 31 (2013) 546–550. [10] K. Ruan, X. Chen, T. Liang, G. Wu, D. Bao, Improved photoluminescence and electrical properties of Eu- and Gd-codoped bismuth titanate ferroelectric thin films, J. Appl. Phys. 103 (2008) 086104. [11] H. Sun, D. Peng, X. Wang, M. Tang, Q. Zhang, X. Yao, Strong red emission in Pr doped (Bi0.5Na0.5)TiO3 ferroelectric ceramics, J. Appl. Phys. 110 (2011) 016102. [12] Z. Yao, H. Li, M. Ma, R. Chu, Z. Xu, J. Hao, G. Li, Preparation and electrical properties of (1 x)SrBi2Nb2O9 xBiFeO3 lead-free piezoelectric ceramics, Ceram. Int. 42 (2016) 5391–5396. [13] W. Xie, L. Su, T. Sa, J. Fu, W. Hu, N. Qin, D. Bao, Strong red emission and electrical properties of highly c-axis oriented Eu3 þ -doped bismuth vanadate ferroelectric thin films, Mater. Chem. Phys. 148 (2014) 854–858. [14] R.-R. Cui, C.-Y. Deng, X.-Y. Gong, X.-C. Li, J.-P. Zhou, Luminescence properties of Eu3 þ doped CaBi2Ta2O9 bismuth layered-structure ferroelectrics, Mater. Res. Bull. 48 (2013) 4301–4306. [15] Y.-M. Kan, G.-J. Zhang, P.-L. Wang, Y.-B. Cheng, Preparation and properties of neodymium-modified bismuth titanate ceramics, J. Eur. Ceram. Soc. 28 (2008) 1641–1647. [16] J. Hou, R.V. Kumar, Y. Qu, D. Krsmanovic, B-site doping effect on electrical properties of Bi4Ti3 2xNbxTaxO12 ceramics, Scr. Mater. 61 (2009) 664–667. [17] X.-P. Jiang, X.-L. Fu, C. Chen, N. Tu, M.-Z. Xu, X.-H. Li, H. Shao, Y.-J. Chen, High performance Aurivillius type Na0.5Bi4.5Ti4O15 piezoelectric ceramics with neodymium and cerium modification, J. Adv. Ceram. 4 (2015) 54–60. [18] Y. Shimakawa, Y. Kubo, Y. Nakagawa, T. Kamiyama, H. Asano, F. Izumi, Crystal structures and ferroelectric properties of SrBi2Ta2O9 and Sr0.8Bi2.2Ta2O9, Appl. Phys. Lett. 74 (1999) 1904.
14854
L. Yu et al. / Ceramics International 42 (2016) 14849–14854
[19] Y. Shimakawa, Y. Kubo, Y. Tauchi, T. Kamiyama, H. Asano, F. Izumi, Structural distortion and ferroelectric properties of SrBi2(Ta1 xNbx)2O9, Appl. Phys. Lett. 77 (2000). [20] E. Subbarao, Crystal chemistry of mixed bismuth oxides with layer-type structure, J. Am. Ceram. Soc. 45 (1962) 166–169. [21] T. Sivakumar, M. Itoh, Ferroelectric phase transitions in new Aurivillius oxides: Bi22xþ Sr1 2xNb2 xScxO9, J. Mater. Chem. 21 (2011) 10865–10870. [22] J. Mercurio, A. Souirti, M. Manier, B. Frit, Phase transitions and dielectric properties in some compounds with bismuth oxide layer structure, Mater. Res. Bull. 27 (1992) 123–128. [23] X.-P. Jiang, X.-L. Fu, C. Chen, N. Tu, M.-Z. Xu, X.-H. Li, H. Shao, Y.-J. Chen, High performance Aurivillius type Na0.5Bi4.5Ti4O15 piezoelectric ceramics with neodymium and cerium modification,, J. Adv. Ceram 4 (2015) 54–60. [24] Y. Wu, M.J. Forbess, S. Seraji, S.J. Limmer, T.P. Chou, C. Nguyen, G. Cao, Doping effect in layer structured SrBi2Nb2O9 ferroelectrics, J. Appl. Phys. 90 (2001) 5296. [25] Z.-Y. Zhou, X.-L. Dong, H.-X. Yan, Lanthanum distribution and dielectric properties of Bi3 xLaxTiNbO9 bismuth layer-structured ceramics, Scr. Mater. 55 (2006) 791–794. [26] H. Chen, B. Shen, J. Xu, J. Zhai, Textured Ca0.85(Li,Ce)0.15Bi4Ti4O15 ceramics for high temperature piezoelectric applications, Mater. Res. Bull. 47 (2012) 2530–2534. [27] P. Fang, P. Liu, Z. Xi, W. Long, X. Li, Structure and electrical properties of new Aurivillius oxides (K0.16Na0.84)0.5Bi4.5Ti4O15 with manganese modification, J. Alloy. Compd. 595 (2014) 148–152.
[28] H. Yan, Z. Zhang, W. Zhu, L. He, Y. Yu, C. Li, J. Zhou, The effect of (Li,Ce) and (K, Ce) doping in Aurivillius phase material CaBi4Ti4O15, Mater. Res. Bull. 39 (2004) 1237–1246. [29] Z. Peng, Y. Chen, Q. Chen, N. Li, X. Zhao, C. Kou, D. Xiao, J. Zhu, Correlation between lattice distortion and electrical properties on Bi4Ti3O12 ceramics with W/Ni modifications, J. Alloy. Compd. 590 (2014) 210–214. [30] D. Peng, H. Sun, X. Wang, J. Zhang, M. Tang, X. Yao, Red emission in Pr doped CaBi4Ti4O15 ferroelectric ceramics, Mater. Sci. Eng. B 176 (2011) 1513–1516. [31] U. Chon, J.S. Shim, H.M. Jang, Ferroelectric properties and crystal structure of praseodymium-modified bismuth titanate, J. Appl. Phys. 93 (2003) 4769. [32] Y. Noguchi, A. Kitamura, L.-C. Woo, M. Miyayama, K. Oikawa, T. Kamiyama, Praseodymium-modified SrBi2Ta2O9 with improved polarization properties at low electric field, J. Appl. Phys. 94 (2003) 6749–6752. [33] Y. Shimakawa, Y. Kubo, Y. Nakagawa, S. Goto, T. Kamiyama, H. Asano, F. Izumi, Crystal structure and ferroelectric properties of ABi2Ta2O9 (A ¼Ca, Sr, and Ba), Phys. Rev. B 61 (2000) 6559. [34] Y. Zhao, H. Fan, G. Liu, Z. Liu, X. Ren, Ferroelectric, piezoelectric properties and magnetoelectric coupling behavior in aurivillius Bi5Ti3FeO15 multiferroic nanofibers by electrospinning, J. Alloy. Compd. 675 (2016) 441–447. [35] Z. Yao, R. Chu, Z. Xu, J. Hao, G. Li, Enhanced electrical properties of (Li,Ce) codoped Sr(Na0.5Bi0.5)Bi4Ti5O18 high temperature piezoceramics, RSC Adv. 6 (40) (2016) 33387–33392. [36] X. Jiang, X. Jiang, C. Chen, N. Tu, Y. Chen, B. Zhang, Photoluminescence and electrical properties of Eu3 þ -doped Na0.5Bi4.5Ti4O15-based ferroelectrics under blue light excitation, Front. Mater. Sci. 10 (2015) 31–37.