KJ Ceramics 31

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Detailed Program

Paper Number : EL-O06

Time Frame : 14:20~14:32

Presentation Date : Friday, 28, November

Session Name : Electronic Ceramics

Session Chair 1# : Eung Soo Kim

Session Chair 2# : Hisao Suzuki

Dielectric Properties and Microstructure Control of (Ba0.7Sr0.25Ca0.05)(Ti0.9Zr0.1)O3 Ceramics

Young Jun Eoh

Kyonggi University

Keywords: Two-step sintering, Ferroelectrics, Microstructure, Dielectric properties

Modified barium titanate (BaTiO3) ceramics have been of great interest and widely investigated for various applications such as multilayer ceramic capacitors (MLCC), electrostrictive actuators, and electromechanical transducers due to their good ferroelectric properties. The general requirements of ferroelectrics are high dielectric constant (εr) and breakdown voltage (Vb) with low dielectric loss (tanδ). To achieve those properties, the dielectric materials should have high relative density and homogeneous microstructure consisting of small grains. It has been reported that the Y2O3, c-ZrO2 and ZnO ceramics sintered by two-step method showed the improved mechanical properties due to their homogeneous microstructure and small grain size. Therefore, the two-step sintering can be effectively applied for improving εr and Vb of the modified barium titanate ceramics without large dielectric loss.
In this study, the dielectric properties and microstructure of (Ba0.7Sr0.25Ca0.05)(Ti0.9Zr0.1)O3 (BSCTZ) ceramics with ZnO (0 ≤ x(wt%) ≤ 0.15) were controlled by various two-step sintering condition. Two-step sintering includes two types of steps. First step is the increasing the temperature (T1) to achieve an intermediate density and obtain proper grain size. Second step is the rapid cooling to second temperature (T2) and holding efficient time to obtain high density. To succeed in two-step sintering method, a sufficiently high relative density (more 70%) needs to be achieved at T1 and proper T2 which have high densification rate should be determined. T1 was changed from 1350oC to 1450oC and the T2 was selected as 1300oC which have maximum densification rate.
For the pure BSCTZ ceramics sintered by two-step method, the specimens showed the higher density and homogeneous microstructure with smaller grain size than those of the specimens sintered by single-step method. Therefore, the Vb of the specimens sintered by two-step method was improved. With increase of T1 from 1350oC to 1450oC, the εr of the specimens increased while the tanδ of the specimens decreased. However, P-E hysteresis loops of the specimens were slightly changed with two-step sintering condition. With increase of ZnO content, the single phase of perovskite structure was observed for all of the specimens. Also, the grain size of the specimens rapidly increased with ZnO addition due to the substitution of Zn2+ for B-site ion. The specimens with 0.1wt% ZnO showed the maximum Vb value, while the both of εr and tanδ were remarkably decreased. This could be attributed to the eliminations of pore and low conductivity of ZnO, respectively. Any frequency dispersions of the dielectric properties were not observed from 1kHz to 1MHz.

References:

[1] K. Maca, V. Pouchly, P. Zalud,J. Eur. Ceram. Soc. 30 (2010) 583.
[2] Y. Mizuno, H. Kishi, K. Ohnuma, T. Ishikawa, H. Ohsato : J. Eur. Ceram. Soc. 27 (2007) 4017.

Acknowledgements : This work was supported by Kyonggi University Research Grant 2014.

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