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Ca$$_x$$Ba$$_{1-x}$$Nb$$_2$$O$$_6$$の高温相における局所構造解析

Local structure analysis of Ca$$_x$$Ba$$_{1-x}$$Nb$$_2$$O$$_6$$ in high-temperature phase

米田 安宏   ; Fu, D.*

Yoneda, Yasuhiro; Fu, D.*

タングステンブロンズ型構造の強誘電体、BaNb$$_2$$O$$_6$$のBaをCaで置換したCa$$_{1-x}$$Ba$$_x$$Nb$$_2$$O$$_6$$ (CBN)では、Caの置換量が0.19 $$le$$ ${it x}$ $$le$$ 0.32の組成範囲で単相の正方晶相が出現する。CBNはセラミックスサンプルにおいても粉末X線回折パターンに超格子反射が現れる。平均構造には収まらない長周期構造が存在している。超格子反射は高温相においてもなお観測されていることから高温相においても構造解析を行った。高温相の平均構造は室温相の局所構造をよく反映していることがわかった。タングステンブロンズ特有のリエントラント相転移を反映した現象だと考えられる。

Ca$$_{1-x}$$Ba$$_x$$Nb$$_2$$O$$_6$$ (CBN) in which Ba of BaNb$$_2$$O$$_6$$ is replaced with Ca, which is a ferroelectric substance having a tungsten bronze structure, A single-phase tetragonal phase appears in the composition range where the amount of Ca substitution is 0.19 $$le$$ ${it x}$ $$le$$ 0.32. For CBN, superlattice reflection appears in the powder X-ray diffraction pattern even in ceramic samples. There is a long-period structure that is deviated from the average structure. Since superlattice reflection is still observed in the high-temperature phase, structural analysis was performed in the high-temperature phase. It was found that the average structure of the high-temperature phase well reflected the local structure of the room temperature phase. It is considered to be a phenomenon that reflects the reentrant phase transition peculiar to tungsten bronze.

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