Fabrication and electrical properties of textured strontium(0.53)barium(0.47)niobium(2)oxygen(6) ceramics prepared by templated grain growth.

摘要

Sr_0.53Ba_0.47Nb₂O₆ (SBN53) ceramics were textured by the templated grain growth (TGG), in a matrix of SrNb₂O₆ and BaNb₂O₆ powders. Acicular KSr₂Nb₅O₁₅ (KSN) template particles, synthesized by a molten salt process, were used to texture the samples in the c direction (i.e., [001]). Template growth was assisted by adding V₂O₅ as a liquid phase former for some compositions. The texture fraction also increased with higher sintering temperatures or times and with initial template concentration due to the preferential growth of the template particles.; When V₂O₅ was present, SBN53 phase formation initiated on the KSN templates and texture development started at temperatures as low as 950°C. Phase formation in the V₂O₅-free samples, however, initiated in the matrix (i.e., independent of the KSN templates). The liquid phase adversely affected the template growth by favoring anisotropic grain growth in the matrix, which caused lower texture fraction and broader texture distribution in [001] at low template concentrations. Increased template-template interaction (e.g., tangling) during tape casting also resulted in broader texture distribution. Therefore, an optimum template content was found to be ∼10–15 wt%. However, a texture fraction of 0.93 to 0.98 was obtained using only 5 wt% templates when anisotropic matrix grain growth was prevented.; Phase evolution was studied in the randomly oriented samples as a function of quenching temperature, heating rate, and liquid phase, using KSN powder (rather than acicular particles) as a seed material. The formation temperature for SBN53 was lowered substantially by adding more seeds, decreasing the heating rate, and introducing a liquid. The temperature decreased from 1260°C for the samples with no seeds to 1130°C for the samples with 15.4 wt% seeds + 0.8 mol% V₂O₅ at a heating rate of 4°C/min. For the V₂O₅-free samples, the activation energy was considerably lowered from 554 ± 15 kJ/mol for the samples with no seeds to 241 ± 17 kJ/mol for the samples with 15.4 wt% seeds.; The dielectric and piezoelectric properties were enhanced in samples with better orientation (i.e., high texture fraction (f) and narrow degree of orientation parameter (r) in the texture direction). The presence of nonferroelectric phases (V₂O₅ or Nb₂O₅-based) at the grain boundaries suppressed the observed dielectric properties, especially at the transition temperature. (Abstract shortened by UMI.)