Institute of Low Temperature and Structure Research, Polish Academy of Sciences, PO Box 1410, 50-950 Wrocław 2, Poland.
J Phys Condens Matter. 2012 Aug 29;24(34):345403. doi: 10.1088/0953-8984/24/34/345403. Epub 2012 Aug 7.
A high-pressure Raman scattering study of wolframite-type Mn(0.97)Fe(0.03)WO(4) is presented up to 10.4 GPa. The phonon wavenumbers vary linearly with pressure. The mode Grüneisen parameters are larger for many bending and lattice modes when compared to the stretching modes due to the larger compressibility of Mn(Fe)O(6) octahedra when compared to WO(6) octahedra. Combining the pressure-dependent Raman data of this work with the temperature-dependent Raman data on this crystal previously reported by us has allowed estimation of the temperature-dependent pure lattice and intrinsic anharmonic contributions to the observed total Raman shifts as a function of temperature. It has been found that the observed unusual hardening of the 884, 698 and 674 cm(-1) stretching modes upon heating from 4 to about 150-200 K followed by the usual softening above 150-200 K is a result of a positive intrinsic anharmonic contribution and a negative pure lattice contribution; i.e., up to about 150-200 K the anharmonic contribution surpasses the lattice contribution and the total Raman shift is slightly positive whereas above 150-200 K the lattice contribution becomes dominant and the Raman bands exhibit the usual softening with increasing temperature.
本文对尖晶石型 Mn(0.97)Fe(0.03)WO(4)进行了高压拉曼散射研究，压力高达 10.4 GPa。声子频率随压力呈线性变化。与伸缩模式相比，许多弯曲和晶格模式的模式 Grüneisen 参数由于 Mn(Fe)O(6)八面体的压缩性大于 WO(6)八面体，因此更大。将这项工作的压力相关拉曼数据与我们之前报道的该晶体的温度相关拉曼数据相结合，我们可以估算出观察到的总拉曼位移随温度变化的温度相关纯晶格和固有非谐贡献。结果发现，在从 4 K 加热到 150-200 K 左右时，观察到的 884、698 和 674 cm(-1)伸缩模式的异常硬化，随后在 150-200 K 以上通常软化，这是由于正的固有非谐贡献和负的纯晶格贡献所致；即在大约 150-200 K 之前，非谐贡献超过晶格贡献，总拉曼位移略为正，而在 150-200 K 以上，晶格贡献变得占主导地位，拉曼带随着温度升高呈现出通常的软化。
