The Phase Formation, Microstructure, and Electric Properties of Tungsten Bronze Ferroelectric Sr2NaNb5O15 Ceramics
The high-density tungsten bronze Sr2NaNb5O15 ceramics without abnormal grain growth were successfully synthesized by a two-step solid-state reaction method in this work. The phase evolution and reaction mechanism in SrNb2O6 and NaNbO3 solid solutions were analyzed by X-ray diffraction and differential scanning calorimetry. The results showed that the Sr2NaNb5O15 phase could exist stably in the temperature range of 1100°–1360°C, and would be decomposed to SrNb2O6 and NaNbO3 phases at temperatures above 1360°C. It was also found that the sintering temperature could significantly affect the density, microstructure, and electric properties of Sr2NaNb5O15 ceramics. When the sintering temperature was 1340°C, the ceramic with a near-theoretical density and a uniform and fine-grained microstructure was obtained, exhibiting outstanding electrical properties: m=2210, tan =0.023, Tc=280°C, Pr=11.71 C/cm2, and Ec=16.15 kV/cm. Further increasing the temperature to 1360°C led to the existence of some molten areas and cracks on the surface of ceramics obtained, which could significantly deteriorate the electric properties. In addition, no abnormal large grains (>50 m) could be found in the system and the reason was also discussed in this paper.
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Document Type: Research Article
Affiliations: Key Laboratory for Macromolecular Science of Shaanxi Province, School of Chemistry and Materials Science, Shaanxi Normal University, Xi'an 710062, Shaanxi, China
Publication date: 01 July 2010