极端条件下新奇化学态的探索

Stoichiometry and atomic ordering state are expected to affect critically the structure and physical properties of the materials. It is important that to investigate the materials with unusual stoichiometric ratio both in theory and experiment. Under extreme conditions, the pressurecan significantly change the atomic bonding by compressing the atomic spacing, so as to change the properties of solid materials.Under high temperature and pressure,the materials with novel chemical state and special physical properties can be synthesized. On the basis of the previous works, our research will focus on the metal halide, metal hydride, high density nitrideand and light elements frameworks and is aimed to fabricate the compounds with novel stoichiometric ratio. By combining of the theory and experiment, we will use USPEX evolutionary algorithm to predict the crystal structures of the compounds and synthesize the compounds with novel chemical state by laser heating diamond anvil cells technique.In situ X-ray diffraction, Raman spectra and electrical transport measurements will completely present the structure and physical properties of these new compounds.

材料中原子的化学计量比和站位可以显著的影响材料的结构和物理性质，研究具有异常化学计量比的材料在理论和实验上都有极为重要的意义。在极端条件下，压力通过缩小原子间距，可以显著地改变原子键合，从而改变固体材料的物性。高温高压下可以合成常压下无法生成的新化学态和具有特殊物理性质的新物质。在已有工作的基础上，本项目将致力于在金属卤化物、金属氢化物、高密度氮化物和轻元素骨架材料中发现具有新奇化学计量比的化合物。通过理论计算和实验的紧密结合，在各种不同的压力和温度条件下，利用USPEX演化算法来预测高压下化合物的晶体结构，采用激光加热金刚石对顶砧技术来合成新化学态物质。原位的X射线衍射、拉曼光谱和电输运测量将完整的呈现这些新化合物的结构和物性。

在极端高温高压条件下，材料会发生许多新奇的变化，比如相变、绝缘体-金属转变和新材料的合成。在本项目的支持下，我们结合金刚石对顶砧装置和脉冲激光加热技术，创造了极端高温高压条件，并且结合瞬态宽带光谱测量方法，研究了一系列材料的绝缘体-半导体-金属化转变行为，比如稀有气体、氮、氢等，文章发表在Science、Nature communications、PNAS、Physics Review Letter等一流期刊，开创了极端条件下材料物性测量的新方法；在此基础上，我们开展了Fe在极端条件下热导率的实验测量，解释了地球早期磁场形成的成因，文章发表在Nature；此外，我们还利用高温高压实验方法开展了大量新材料的合成，例如富氢高能材料、富氮高能材料、超硬等功能材料。按照项目预期计划圆满地完成了各项研究目标。

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