The pressure-induced structural phase transitions in bismuth tungstate Bi₂WO₆ have been studied using neutron diffraction and Raman spectroscopy at high pressures up to 7 and 30 GPa, respectively. A rich structural polymorphism was revealed. At P ≃ 3.5 GPa a phase transition from the initial orthorhombic phase of P2₁ab symmetry to an orthorhombic phase of B2cb symmetry was observed. This transition is caused by the complex spatial rotation of the WO₆ octahedra. A subsequent isostructural phase transition to another orthorhombic phase of B2cb symmetry was detected at P ≃ 5.9 GPa, accompanied by changes in both the mutual rotation and tilting of the oxygen octahedra with respect to the crystal b axis. Two more pressure-induced phase transitions in Bi₂WO₆ at high pressures of 11.5 and 20 GPa were observed in the Raman spectra. These pressure-driven phase transitions in bismuth tungstate are accompanied by anomalies in the pressure dependences of the unit-cell parameters, bond lengths and angles, and in the vibrational modes.

中文翻译：

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钨酸铋 Bi2WO6 中的压力诱导结构相变

使用中子衍射和拉曼光谱分别在高达 7 和 30 GPa 的高压下研究了钨酸铋 Bi ₂ WO _{6 中}压力诱导的结构相变。揭示了丰富的结构多态性。在P ≃ 3.5 GPa 时，观察到从P 2 ₁ ab对称的初始正交相到B 2 cb对称的正交相的相变。这种转变是由 WO ₆八面体的复杂空间旋转引起的。随后的同构相转变到另一个B 2 cb对称的正交相在P ≃ 5.9 GPa，伴随着氧八面体相对于晶体b轴的相互旋转和倾斜的变化。在拉曼光谱中观察到在 11.5 和 20 GPa 的高压下Bi ₂ WO ₆中的另外两个压力诱导相变。钨酸铋中这些压力驱动的相变伴随着晶胞参数、键长和角度以及振动模式的压力依赖性异常。