Unified view for pressure-induced successive changes from amorphization to re-entrant crystallization

提出了“变尺寸单元间空间构型热力学优化”的新思想。在此基础上，作者试图解释由上传压力引起的一系列结构变化。为此，选择分子晶体四碘化锡作为原型物质，其经历压力诱导的非晶化，然后再进入结晶。如果锡原子被假定占据由碘组成的主晶格的四面体间隙位置，那么只要锡总是以四个碘作为最近的邻居，在寻找可能的占据位置时就会出现挫折。根据这一规则，低压相结构自动地出现为没有任何挫折的情况。然而，随着锡人口的增加，挫折感也随之增加。局部能量的挫折网站变得更高相比，nonfrustated网站。然后，通过适当地分配局部能量，可以写出哈密顿量。不 关于我们 由此，通过最小化由哈密顿量得到的自由能，定性地解释了一系列的结构变化，这一思想可以用来描述多晶现象的物理起源。很自然地推断，四碘化锡将发生压力诱导的液-液转变。事实上，从低压结晶相的熔化曲线中发现，在约1.5GPa处具有断裂，超过该断裂，熔化曲线变得几乎平坦。这表明低压液体的密度不同于高压侧的密度。最后，我们已经成功地显示了直接的证据，存在的两种液体具有不同的局部结构进行原位同步X射线衍射实验。当在平均场近似下处理时，本思想产生正则解处理。在此基础上，建立了四碘化锡的相图，包括新的临界点和调幅线。少

A new idea of "thermodynamic optimization for spatial configuration among elements with variable size" is proposed. On the basis of this idea the reporter has tried to explain a series of structural changes induced by uploading pressure. To this end, a molecular crystal tin tetraiodide was chosen as a prototype substance, which undergoes pressure-induced amorphization followed by re-entrant crystallization. If tin atoms are assumed to occupy the tetrahedral interstitial sites of the host lattice made of iodines, frustration will come up in finding possible occupation sites as far as the tin does always take four iodines as nearest neighbors. According to this rule the lower-pressure phase structure automatically appears as a case without any frustration. However, frustration develops with increasing tin population. The local energy of the frustrated site becomes higher as compared to nonfrustated site. The Hamiltonian can then be written down by suitably assigning the local energies. T … More he series of structural variations were thus qualitatively explained by minimizing the free energy obtained through the Hamiltonian.The idea can be adapted to describe the physical origin of polyamorphism. It is naturally inferred that a pressure-induced liquid-to-liquid transition will take place in tin tetraiodide. In fact, from the melting curve of the low-pressure crystalline phase was found to have a break at around 1.5 GPa, beyond which the melting curve becomes almost flat. This suggests that the density of the low-pressure liquid differs from that on the higher-pressure side. Finally, we have succeeded in showing direct evidence for the existence of the two liquids with different local structures by conducting in situ synchrotron x-ray diffraction experiments. The present idea yields, when treated within mean-field approximation, a regular solution treatment. The phase diagram of tin tetraiode was constructed within this framework, which included a new critical point and spinodal lines. Less