Thermally induced structural changes in incommensurate calcium barium niobate Ca{sub 0.28}Ba{sub 0.72}Nb{sub 2}O{sub 6} (CBN28)
Thermally induced structural changes in incommensurate calcium barium niobate Ca{sub 0.28}Ba{sub 0.72}Nb{sub 2}O{sub 6} (CBN28)
复制标题
不相称铌酸钙钡 Ca{sub 0.28}Ba{sub 0.72}Nb{sub 2}O{sub 6} (CBN28) 的热致结构变化
DOI：
10.1016/j.jssc.2012.06.028
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发表时间：
2012
影响因子：
3.3
通讯作者：
M. Muehlberg
中科院分区：
文献类型：
--
作者：
J. Schreuer;M. Burianek;M. Muehlberg
弛豫铁电 CBN28 的不通约调制晶体结构在 3+2 维超空间群 P4bm(αα1/2,−αα1/2) 中在高达 330°C 的高温下得到细化。主要由 NbO6 八面体的协同倾斜和大阳离子位点 Me2 的占位调制组成的结构调制持续超出扩散铁电转变，幅度略有减小。没有观察到对称性的变化。两个对称非等价的 NbO6 八面体都因 Nb 原子沿四方 c 轴在相同方向上的偏心位移而扭曲。 Nb原子的位移随着温度的升高而逐渐减小，直到其中一个Nb原子在转变温度T附近穿过其配位多面体的中心，采用无补偿的反铁电构型。这种变化伴随着 Nb 原子沿 c 轴的热运动增强。结构扭曲和电极化在 TM 处不会完全消失，但可能会持续存在于波动的极性纳米域中。
The incommensurately modulated crystal structure of relaxor ferroelectric CBN28 was refined at elevated temperatures up to 330°C in the 3+2 dimensional superspace group P4bm(αα1/2,−αα1/2). The structural modulations mainly consisting of cooperative tilting of NbO6octahedra and an occupational modulation of the large cation site Me2 persist beyond the diffuse ferroelectric transition with slightly reduced amplitudes. A change of symmetry was not observed. Both symmetrically non-equivalent NbO6octahedra are distorted by off center shifts of the Nb atoms in the same direction along the tetragonal c-axis. The displacements of the Nb atoms are gradually reduced with increasing temperatures until one of the Nb atoms crosses the center of its coordination polyhedron near the transition temperature TMadopting an uncompensated anti-ferroelectric configuration. This change is accompanied by enhanced thermal motions of the Nb atoms along the c-axis. Structural distortions and electric polarization do not completely vanish at TMbut may persist in fluctuating polar nanodomains.