第一性原理研究硫化镉高压相变及其电子结构与弹性性质

采用第一性原理研究了CdS的六方纤锌矿(WZ), 立方闪锌矿(ZB) 和岩盐矿(RS)相在高压条件下的相稳定性、 相变点、电子结构以及弹性性能.WZ相与RS 相可以在相应的压强范围内稳定存在, 而ZB相不能稳定存在.压强大于2.18 GPa时, WZ相向RS相发生金属化相变.WZ相中S原子电负性大于Cd, 且电负性差值小于1.7, CdS的WZ相为共价晶体.高压作用下, S原子半径被强烈压缩, 有效核电荷增加, 对层外电子吸引能力提高, 电负性急剧增大, 导致S与Cd的电负性差值大于1.7, CdS的RS相以离子晶体存在. WZ相的C₄₄随压强增加呈下降趋势, 导致WZ相力学不稳定, 并向RS相转变.当压强大于2.18 GPa时, RS相C₁₁, C₁₂随压强增加而增大, 并且C₄₄保持稳定, 说明RS相具有良好的高压稳定性与力学性能.关键词：第一性原理相变电子结构弹性性质

First-principles study of pressure induced phase transition,electronic structure and elastic properties of CdS

In this work, phase stabilities, phase transitions, electronic structures and elastic properties of wurtzite structure (WZ), zinc-blende structure (ZB) and rocksalt struture (RS) phase of CdS are studied by first principles method. Results indicate that WZ and RS phases could be stable in corresponding pressure areas. However, ZB phase could not be stable. Pressure-induced metallic phase transition from WZ to RS will occur at 2.18 GPa. Electronegativity of S atom in WZ phase is much more than that of Cd atom, and the difference in electronegativity between S and Cd is less than 1.7, which induces covalent crystal of CdS. Under the condition of high pressure, radius of S is reduced sharply, which causes the increase of effective nuclear charge. Large nuclear charge will enhance the ability to attract electrons of outer shell, which will cause larger electronegativity. When pressure is higher than 2.18 GPa, the difference in electronegativity is more than 1.7. Then, CdS will be ionic crystal. C₄₄ of WZ phase decreases with pressure, resulting in mechanical instability. And then,the WZ-to-RS phase transition occurs at 2.18 GPa. Moreover, C₁₁ and C₁₂ of RS phase increase with pressure. At the same time, C₄₄ of RS is stable with pressure increasing entirely, all of which shows that RS phase has excellent stability and mechanical property under high pressure.
Keywords：first principlephase transitionelectronic structureelastic properties