第五副族元素动-静熔化线差异的关键问题研究

The science about matters under extreme compression is the basis for perception, understanding, and then to design and precisely control the dynamical response of materials. The well-known discrepancy in the melting curve of transition metals measured by dynamic and static loading methods is a long standing but important and fundamental conundrum in this field. To pursue an ultimate solution for this problem will drive forward a fast development in the high pressure physics and technology, as well as to enhance our prediction and control capability in material science. This proposal focuses on the group VB metals, which are believed having both huge discrepancy in the dynamic and static melting curves and anomalous solid-solid phase transition and shear softening simultaneously. By carrying out an ensemble of dynamic and static high-pressure measurements and theoretical simulations, we will attempt to deepen the comprehension about the physical processes and relevant effects in both dynamic loading and static laser heating diamond anvil cell (DAC) loading. With such a systematic investigation on the law that governs the high pressure melting, shear softening and anisotropy, structure stability, and properties variation, as well as their connections, we will acquire reliable phase boundaries for solid-solid and solid-liquid transitions, and the P-T phase diagram as well. This achievement might provide a complete and self-consistent verification and validation about the discrepancy in the dynamic and static melting curves of transition metals, and recognize the clues or unique understanding about the potential candidate for the possible physical mechanism.

极端压缩状态下的物质科学是认识、理解、设计和控制材料动态响应行为的基础。过渡金属动-静高压熔化线差异问题是这一学科领域长期未解的重要基础科学难题，寻求对该问题的解决必将推动高压领域科学技术的快速发展，加深加强对物质行为的预测和控制能力。本项目拟从具有动-静熔化线差异且同时具有剪切反常软化和固-固相变的第五副族元素入手，结合动、静高压测量和理论模拟，深入理解动、静高压不同加载方式下的物理过程及效应，系统研究第五副族金属的高压熔化、剪切软化、结构和物性等的规律变化及相互间的关联，并与实验测量结果相互结合、印证，以期获得可靠的固-固、固-液相边界及压力-温度相图，并对该组元素的动-静熔化线差异问题给出系统、可靠的检验和验证，寻找可能的物理机制，为解决过渡金属动-静高压熔化线差异提供新线索和新认识。

过渡金属由于具有独特且优异的性能而在工业工程中得到广泛应用。这些性能与d壳层电子的量子行为密切相关。第五副族元素的d壳层接近半填满的，具有非常典型的过渡金属特性，并导致了各种反常，其中被文献广泛报道的高压下过渡金属动-静熔化线差异问题即被猜测与此密切相关。为了解决其中的关键物理问题，我们自主开发了晶体弹性性质高通量计算程序和冲击雨贡纽与等熵线高效计算程序，发现了金属钒和铌中独特的密度泛函理论的过局域化偏差，并建立了DFT+J唯象方法。在此基础上，开展了大规模第一原理电子结构计算和分子动力学模拟，排除了粘性流体假定、排除了外部环境可能的影响，预测了温度驱动的钒RH-BCC逆相变，预测了金属钒和铌弹性常数和冲击声速的“压致软化-热致硬化”双重反常，预测了金属钒和铌可靠的高压熔化曲线，建立了高压相变-力学性质反常-熔化曲线反常之间的物理关联。开展了一系列动高压实验和基于激光加热DAC的静高压实验，获得了可靠的高压声速数据、晶体结构信息和动-静高压熔化温度数据，实验证实了温度驱动钒RH-BCC逆相变、证实了金属钒模量和声速的“压致软化-热致硬化”双重反常，意外发现冲击路径下的BCC-RH1-RH2结构相变，获得了理论-动-静高压实验完全自洽一致的熔化曲线。结果否定了动-静高压熔化线差异与d电子行为有关这一假定，也否定了其与过渡金属有关。并将之前的动-静熔化线数据差异溯源至实验技术的缺陷，而非过渡金属元素本身的物理特性，澄清了关于动-静高压熔化线问题的物理本源，并最终获得了可靠的金属钒高压结构相图。这一科学认识上的重大进步或将推动高温高压实验技术向精密化发展。通过本项目的研究，建立了系统的金属材料高压熔化特性精密研究实验和理论模拟方法，获得了关于第五副族元素和d电子行为的新认识，为探索或设计更广泛的高压材料体系，特别是含f电子的关联金属体系奠定了基础，并为理解极端压缩条件下物质的普遍特性提供了有益参考。