High-pressure electronic structure and phase transitions in monoclinic InSe:: X-ray diffraction, Raman spectroscopy, and density functional theory
High-pressure electronic structure and phase transitions in monoclinic InSe:: X-ray diffraction, Raman spectroscopy, and density functional theory
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DOI：
10.1103/physrevb.77.045208
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发表时间：
2008-01-01
影响因子：
3.7
通讯作者：
Chevy, A.
中科院分区：
文献类型：
--
作者：
Errandonea, D.;Martinez-Garcia, D.;Chevy, A.
我们研究了单斜（MC）InSe的晶体结构和电子结构，发现在压力下的Hg 2Cl 2-like tetraxide相的可逆相变。通过角色散X射线衍射和拉曼光谱在金刚石压砧单元中研究了晶体结构的压力演化，压力高达30 GPa。从衍射实验中，我们推断MC InSe在压力下逐渐变得更加对称，在19.4 +/- 0.5 GPa下将晶体结构转变为四方结构。这种相变在没有任何体积变化的情况下发生。压力下的拉曼测量证实了单斜晶系到四斜晶系转变的发生。MC相中的非简并模，特别是A（g）（4）模，表现出负压力系数，与B-g（1）模收敛，在四方相转变为Eg模。通过密度泛函理论（DFT）的电子结构和总能量计算对实验结果进行了解释，结果表明，在18 GPa以上，四元相是最稳定的相.它还表明，沿着从单斜到四斜InSe的连续变化，有一个渐进的减少的带隙，并最终在四斜相，有一个小的带重叠。然而，拉曼效应和光吸收测量表明，这种重叠可能是由于通常的DFT带隙低估。四面体InSe很可能是一种低带隙半导体。比较了单斜相和四斜相InSe的成键情况。
We have studied the crystal and electronic structure of monoclinic (MC) InSe under pressure finding a reversible phase transition to a Hg2Cl2-like tetragonal phase. The pressure evolution of the crystal structure was investigated by angle-dispersive x-ray diffraction and Raman spectroscopy in a diamond-anvil cell up to 30 GPa. From the diffraction experiments, we deduced that MC InSe becomes gradually more symmetric under pressure, transforming the crystal structure into a tetragonal one at 19.4 +/- 0.5 GPa. This phase transition occurs without any volume change. Raman measurements under pressure confirmed the occurrence of a monoclinic-to-tetragonal transformation. The nondegenerate modes in the MC phase, especially the A(g)(4) modes, exhibit a negative pressure coefficient, converging with the B-g(1) modes, and becoming an Eg mode in the tetragonal phase. The experimental results are interpreted through density-functional theory (DFT) electronic-structure and total-energy calculations, which showed that beyond 18 GPa the tetragonal phase is the most stable phase. It is also shown that along the continuous change from monoclinic to tetragonal InSe, there is a progressive decrease of the band gap and eventually, in the tetragonal phase, there occurs a small band overlap. However, the Raman-effect and optical-absorption measurements suggest that this overlap is probably due to the usual DFT band-gap underestimation. Tetragonal InSe is most likely a low-gap semiconductor. The bonding in the monoclinic phase and that in the tetragonal InSe phase are compared.