非静水压下过渡金属钼的相变机理及物态方程研究

The ultrahigh pressure equation of state of Molybdenum (Mo), a calibration standard, plays a very important role in the implosion dynamics. To determine the phase diagrams of Mo at high pressure (P) and temperature (T), including melting curve, is a longstanding problem. Though some experimental and theoretical investigations showd that there is a solid-solid phase transition under hydrostatic pressure. But the phase transition and the mechanism under non-hydrostatic pressure remains inconclusive up to now. In this work, we will investigate the mechanism of phase transition and equation of state of Mo under non-hydrostatic pressure from calculations. The ab-initio molecular dynamic simulations combined with the lattice dynamics will be employed to obtain the phase diagram and thermodynamic properties of Mo. The theoretical method contains the anharmonic effects at high temperature. And we will also investigate the dynamics mechanism of the phase transition of Mo under shock compression by molecular dynamic simulations. And then the high pressure melting curve of Mo will be investigated. From this work, we try to clarify the scientific disputation on the high pressure melting of transition metals. And it is contributing to construct the database of standard reference materials and the multi-phase equation of state of transition metal under high pressure.

难熔金属钼是超高压实验中的标准材料，其高压相变问题（包括固-固相变及固-液相变）在国内外动、静高压实验及理论计算三者之间存在极大的科学争议。前期理论研究表明钼在静水压下存在固-固相变，但非静水压下的相变信息及机理并不明确。因此，本项目拟采用理论计算，研究非静水压下钼的相变及物态方程问题。采用第一性原理分子动力学结合晶格动力学方法，充分考虑高温下非谐效应的影响，获取钼的高温高压相图及宽区物态方程；引入剪应力作用，分析冲击加载下钼的相变动力学机理；进而研究非静水压下钼的熔化曲线，尝试解决难熔金属在动静高压熔化问题上的巨大差异；同时为建立标准材料物态方程数据库、构建高压下金属多相物态方程模型提供有益参考。

难熔金属钼是超高压实验中的标准材料，其高压相变问题（包括固-固相变及固-液相变）在国内外动、静高压实验及理论计算三者之间存在极大的科学争议。前期理论研究表明钼在静水压下存在固-固相变，但非静水压下的相变信息及机理并不明确。因此，本项目拟采用理论计算，研究非静水压下钼的相变及物态方程问题。采用分子动力学结合晶格动力学方法，充分考虑高温下非谐效应的影响，获取钼的高温高压相图及宽区物态方程；引入剪应力作用，分析冲击加载下钼的相变动力学机理；进而研究非静水压下钼的熔化曲线，尝试解决难熔金属在动静高压熔化问题上的巨大差异；同时为建立标准材料物态方程数据库、构建高压下金属多相物态方程模型提供有益参考。在完成本项目的同时，我们对其他一系列过渡金属及其合金的高压相变问题进行了深入研究，如Ti，Zr，Fe，Ni-Ti合金，Ce-La合金以及Fe3C化合物等。