高压下钨酸锆晶体-非晶体相变的机制研究

Pressure-induced amorphization plays an important role in many physical processes and it is a promising approach for the commercial production of amorphous materials. A large number of investigations have been devoted to unfolding a variety of this fascinating phase transformation’s aspects under high pressure. However, owing to the difficult on techniques, two fundamental problems concerning the microscopic mechanism remain unsolved: (1) is this phase transition first order? (2) what is the transformation kinetics? The mechanism for amorphization in zirconium tungstate is particularly interesting since crystalline zirconium tungstate shows some unusual properties including isotropic negative thermal expansion and pressure induced elastic softening, which are believed to be theoretically linked with pressure-induced amorphization. In this project we propose to measure the volume change using strain gauge method and monitor the temperature variation by differential thermal analysis during the pressure-induced amorphization of zirconium tungstate. According to the volume/temperature variations we can make a judgment about is it a first order transformation. Meanwhile, we will investigate the transformation kinetics using a combination of strain gauge method, x-ray diffraction, neutron diffraction, Raman spectrum and Transmission electron microscope. This study is relevant to our understanding of the pressure induced amorphization and will supply experimental evidences for testing various theoretical models.

压力诱导的晶体-非晶相变广泛地存在于自然界中并有望用于工业制备大尺寸非晶材料。尽管已有大量的工作致力于研究这一现象，由于技术原因还有两个重要问题有待回答：（1）这一相变是一级相变吗？（2）这一相变的动力学过程是怎样的？钨酸锆是已知具有最大各向同性负热膨胀系数的材料，其在高压下的晶体-非晶相变与负热膨胀性质以及压致软化性质具有紧密的内在联系，因此钨酸锆高压下的晶体-非晶相变研究对于理解负热膨胀现象以及压致软化现象也具有重要意义。本课题拟用应变计方法测量钨酸锆在晶体-非晶相变过程中的体积变化，用原位差热分析方法测量相变时的温度变化。根据体积变化和温度变化我们可以判断这个相变是否是一级相变。同时我们将用应变计方法、原位X射线衍射、中子衍射和透射电子显微镜技术研究这一相变的动力学过程。本研究将加深对压力诱导的晶体-非晶相变机制的理解，提供可以用以甄别不同理论模型的实验数据。

压力诱导的晶体-非晶相变存在于许多材料中，相关研究对于地学和材料科学都有重要意义。尽管已有大量的工作致力于研究这一现象，由于技术原因还有两个重要问题有待回答：（1）这一相变是一级相变吗？（2）这一相变的动力学过程是怎样的？钨酸锆是已知具有最大各向同性负热膨胀系数的材料，其在高压下的晶体-非晶相变与负热膨胀性质以及压致软化性质具有紧密的内在联系，因此钨酸锆高压下的晶体-非晶相变研究对于理解负热膨胀现象以及压致软化现象也具有重要意义。本项目利用电阻应变计方法测量了钨酸锆在晶体-非晶相变过程中的体积变化，用原位差热分析方法测量相变时的温度变化。根据体积变化和温度变化我们判断出这一相变是一级相变。同时我们用应变计方法、原位X射线衍射、中子衍射和透射电子显微镜技术研究了这一相变的动力学过程，我们的实验数据表明，此相变主要是受成核过程控制，几乎没有核的长大过程。本研究将加深我们对压力诱导的晶体-非晶相变机制的理解，提供可以用以甄别不同理论模型的实验数据。