High-temperature single-crystal X-ray diffraction study of tetragonal and cubic perovskite-type PbTiO3 phases.
High-temperature single-crystal X-ray diffraction study of tetragonal and cubic perovskite-type PbTiO3 phases.
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DOI：
10.1107/s2052520616005114
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发表时间：
2016-06
期刊：
影响因子：
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通讯作者：
A. Yoshiasa;T. Nakatani;A. Nakatsuka;M. Okube;K. Sugiyama;T. Mashimo
中科院分区：
文献类型：
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作者：
A. Yoshiasa;T. Nakatani;A. Nakatsuka;M. Okube;K. Sugiyama;T. Mashimo
对合成的PbTiO3钙钛矿在298 ~ 928k宽温度范围内进行了高温单晶x射线衍射研究。在753 K附近发现了从四方相（P4mm）到立方相（Pm \bar 3 m）的转变。在非中心对称的P4mm对称群中，Pb和O原子沿c轴的相对位移差远大于Ti和O原子的相对位移差。与O原子的位移相比，Pb和Ti离子对极化向相反方向移动有充分的贡献。偏离四方相德拜-沃勒因子和成键距离的线性变化可以解释为相变前的前兆现象。O的温度因子Ueq在过渡点附近出现扰动，而Pb和Ti的Ueq值随温度的升高而不断变化。O位在立方相中包含明显的构型紊乱。极性局部位置畸变存在于立方相中，被认为是产生对电性的原因。Pb和Ti的德拜温度ΘD估计值在四方相中分别为154和467 K，在高温相中下降22%。相变后，Pb和Ti的有效电位发生了明显的变化，并变软。
A high-temperature single-crystal X-ray diffraction study of a synthetic PbTiO3 perovskite was carried out over the wide temperature range 298-928 K. A transition from a tetragonal (P4mm) to a cubic (Pm \bar 3 m) phase has been revealed near 753 K. In the non-centrosymmetric P4mm symmetry group, the difference in relative displacement between Pb and O along the c-axis is much larger than that between Ti and O. The Pb and Ti cations contribute sufficiently to polarization being shifted in the opposite direction compared with the shift of O atoms. Deviation from the linear changes in Debye-Waller factors and bonding distances in the tetragonal phases can be interpreted as a precursor phenomenon before the phase transition. Disturbance of the temperature factor Ueq for O is observed in the vicinity of the transition point, while Ueq values for Pb and Ti are continuously changing with increasing temperature. The O site includes the clear configurational disorder in the cubic phase. The polar local positional distortions remain in the cubic phase and are regarded as the cause of the paraelectricity. Estimated values of the Debye temperature ΘD for Pb and Ti are 154 and 467 K in the tetragonal phase and decrease 22% in the high-temperature phase. Effective potentials for Pb and Ti change significantly and become soft after the phase transition.