负热膨胀材料钨酸钇的快速合成及其Raman光谱(英文)

RAPID SYNTHESIS AND RAMAN SPECTRA OF A NEGATIVE THERMAL EXPANSION MATERIAL OF YTTRIUM TUNGSTATE

用二氧化碳激光快速凝固技术合成了负热膨胀材料钨酸钇。场发射扫描电子显微镜和X射线衍射分析表明:二氧化碳激光快速凝固技术合成的钨酸钇(Y2W3O12)为正交相的层状致密块体。Y2W3O12由于在大气中存放后会形成 Y2W3O12·xH2O, Raman光谱研究表明:其中的水分子不仅能阻碍其共享顶角多面体的摇摆,而且将阻碍每一种振动。低于388 K,所释放的水分子对[WO4]四面体内振动的影响较小,在该温度以上能够释放的水分子对 Y2W3O12框架结构中的多面体的摇摆运动、伸缩振动、弯曲振动、天平动和平动均有较大的阻碍作用。变温 Raman光谱揭示:不仅低频声子模,而且高频光学声子模对负热膨胀也有贡献。

A negative thermal expansion material of yttrium tungstate was synthesized by rapid solidification with a CO2 laser. The yttrium tungstate is a bulk material with a densely packed layer structure and orthorhombic phase, shown by field emission-scanning electron microscopy and X-ray diffraction. Y2W3O12 can be changed to form Y2W3O12·xH2O by adsorbing water in air after being stored at ambient atmosphere. Raman spectra reveal that the presence of water molecules in the material affects not only the rocking motion, but every type of motion of the corner-shared polyhedra. It is shown that the water molecules that could be released below 388 K have little influence on the vibrations of the [WO4] tetrahedra, whereas those that could be released above this temperature hinder not only the rocking, but also the stretching, bending, librational and translational motions of the polyhedra in the Y2W3O12 framework. The temperature dependence of the Raman spectra reveals that not only the low frequency modes, but also the higher optical phonon modes contribute to the negative thermal expansion as well.