晶体化学新领域——高压相变晶体化学

New Special Field of Crystal Chemistry:High-Pressure Phase Transition Crystal Chemistry

用X射线衍射的方法衡量原子及离子的尺寸并测定其晶体结构是人类进入微观世界最为关键的一步。在通常的温度和压力下各种原子及离子的结合方式及排布规则已在晶体化学中得到详尽的阐述。笔者着重探讨了在高压下离子化合物及矿物的晶体化学特点。在高压下随着压力的增加,氧化物及硅酸盐中阳离子会发生从低配位数多面体向高配位数的多面体的迁移。这种迁移是由于阴阳离子半径比值改变所致。计算了不同的SiO2多形中氧和硅的离子半径,表明氧离子半径随压力增加而不断缩小,硅离子半径却随着压力的增加及相变的发生而逐渐增大,这种现象可能是由于离子化合物向金属相转变的结果。

The method which use X ray diffraction to measure the size of atom and ion and determine crystal structure is most important step for mankind get into microscopic view world. At usual temperature and pressure, the connection pattern and the arrange- ment rule of various atom and ion have already elaborated in the crystal chemistry in detail. In this paper, the study on the crystal chemistry characteristics of ionic compounds and minerals was emphasized under high pressure. Under high pressure when the pressure increases, the cations of silicon in oxide or silicate minerals occurred migration from low coordination number polyhedra to high coordination number polyhedra. This migration is due to the change with radius ratio of cations to anions. Under high pressure the ionic radii of oxygen and silicon have been calculated for different SiO2 polymorphs. It is indicated that the ionic radius of oxygen is decreasing gradually with the increase of pressure, but the cation radius of silicon is increasing with the increase of pressure and the occurrence of phase transitions. This kind of phenomenon may be due to the transition from ionic compounds to metallic phases under high pressure.