New high-pressure tetragonal polymorphs of SrTiO 3 —molecular orbital and Raman band change under pressure
New high-pressure tetragonal polymorphs of SrTiO 3 —molecular orbital and Raman band change under pressure
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新型高压四方多晶型SrTiO 3 – 分子轨道和拉曼带在压力下的变化
DOI：
10.1088/1361-648x/aabef3
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
Yan, Hao
中科院分区：
文献类型：
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作者：
Yamanaka, Takamitsu;Ahart, Muhtar;Mao, Ho-kwang;Yan, Hao
用拉曼光谱、同步辐射x射线粉末衍射和从头算分子轨道计算研究了SrTiO3的振动和结构性质。这些测量和计算揭示了在约9 GPa时从立方相到四方相的结构转变。在9 Gpa以上，新的峰更尖锐，与四方结构有关。在大约30 GPa时，一些谱带消失了，出现了几个新的谱带。Rietveld轮廓拟合分析发现，在30 Gpa以上，P4/MBM发生了从I4/MCM到P4/MBM新结构的转变。衍射图没有显示出CMCM的正交相。从头算证明了分子轨道耦合的变化伴随着结构的变化。在立方相中，钛的穆利肯电荷随压力的增加而增加，而锶的电荷则持续减少。随着压力的增加，Ti-O键的d-p-π杂化和局域电子密度降低。在P4/MBM相中，Ti-O键变短，Ti电荷的变化更加加速。X射线衍射谱、拉曼光谱和分子轨道计算都得到了一致的结果。
The vibrational and structural properties of SrTiO 3 were investigated using Raman spectroscopy, synchrotron x-ray powder diffraction up to 55 GPa at 300 K, and ab initio quantum chemical molecular orbital (MO) calculations. These measurements and calculations revealed the structure transformation from cubic to tetragonal phase at about 9 GPa. Above 9 GPa, sharper new peaks were associated with a tetragonal structure. At about 30 GPa some bands disappeared and several new bands emerged. Structure transformation from I4/mcm to a new structure of P4/mbm was found at above 30 GPa by Rietveld profile fitting analysis. The diffraction pattern gave no indication of a Cmcm orthorhombic phase. Ab initio MO calculation proved the change of the molecular orbital coupling with a structure transformation. The Mulliken charge of Ti is increased with increasing pressure in the cubic phase, but the Sr charge continuously decreased. The d–p–π hybridization of the Ti–O bond and localizing the electron density are decreased with increasing pressure. The Ti–O bond becomes shorted in the P4/mbm phase and the change in the Ti charge accelerated more. All present investigations by x-ray diffraction, Raman spectra study and MO calculation show consistent results.