Barium Strontium Titanate Ceramics Prepared by a Reaction-Sintering Process
- PDF / 228,916 Bytes
- 6 Pages / 595 x 842 pts (A4) Page_size
- 41 Downloads / 242 Views
FF3.3.1
Barium Strontium Titanate Ceramics Prepared by a Reaction-Sintering Process Yi-Cheng Liou, Jen-Hsien Chen and Chi-Ting Wu Department of Electronic Engineering, Kun-Shan University of Technology, Tainan Hsien 710, Taiwan, R.O.C. ABSTRACT Barium strontium titanate (Ba0.7Sr0.3TiO3, BST) ceramics prepared by a reaction-sintering process were investigated. The mixture of raw materials of stoichiometric Ba0.7Sr0.3TiO3 was pressed and sintered into ceramics without any calcination stage involved. Perovskite BST ceramics were obtained after sintered at 1330-1370oC for 2-6 h. For 6 h soak time, a density value 5.68g/cm3 (99.8% of the theoretic value) was obtained at 1350oC sintering. Grains of sizes between 2µm and 15µm were formed after 1330-1370oC sintering for 2-6 h. A diffused ferroelectric-paraelectric transition was observed in pellets sintered at 1330oC for 2 h and disappeared at a longer soak time or a higher sintering temperature.
INTRODUCTION BaTiO3 (BT) ceramic is a typical ferroelectric material with Curie temperature about 130oC. It has been extensively used in multilayer ceramic capacitors (MLCCs) [1,2], positive temperature coefficient (PTC) thermistors [3] and piezoelectric transducers. In BaxSr1-xTiO3 (BST) system for x0.4 at 1350oC and 1400oC sintering. At 1450oC, fine matrix grains were not observed even with x=0.6. The transition broadening was not observed as the fine matrix grains disappeared [27]. This could be the reason why the diffused transition disappeared at 1350oC and 1370oC in Figure 5. Fine grains about 2µm were observed at 1330oC/2 h sintering and grains of 3.44µm formed after 1350oC/2 h sintering. Hench and West proposed that the ferroelectric transition of BT is gradual in the case of fine particles (1 to 2 µm). This is different from the extremely sharp transition in the single crystalline BT. They thought there is a relationship between the size of the crystalline structure and the equilibrium positions of titanium ions in the polarized state. The increase in dielectric constant at Curie temperature is much less for ultra fine particles (0.2µm). The domain orientation in an ultra fine powder is random and this tends to broaden the ferroelectric transition [31]. The diffused transition was not observed in BST ceramics sintered at 1330-1370oC for 4 h in figure 6. The peak dielectric constant increased from 9200 at 1330oC to 14000 at 1370oC. The K-T curves of BST ceramics sintered at 1330-1370oC for 6 h are shown in figure 7. Normal ferroelectric K-T curves are observed.
CONCLUSIONS Perovskite Ba0.7Sr0.3TiO3 ceramics could be obtained by a simple and effective reaction-sintering process successfully. Density increased with sintering temperature for 2 h and 4 h soak time at 1330-1370oC. For 6 h soak time, a density value 5.68g/cm3 (99.8% of the theoretic value) was obtained at 1350oC sintering. Grains of sizes between 2µm and 15µm were formed after 1330-1370oC sintering for 2-6 h. A diffused ferroelectric-paraelectric transition was
Figure 5. Temperature dependence of the dielectr
Data Loading...
