HIGH-PRESSURE ELECTRONIC STRUCTURE AND PHASE TRANSITIONS IN MONOCLINIC InSe: X-RAY DIFFRACTION, RAMAN SPECTROSCOPY, AND DENSITY FUNCTIONAL THEORY

摘要: We have studied the crystal and electronic structure of monoclinic (MC) InSe under pressure finding a reversible phase transition to ${\mathrm{Hg}}_{2}{\mathrm{Cl}}_{2}$-like tetragonal phase. The evolution was investigated by angle-dispersive x-ray diffraction Raman spectroscopy in diamond-anvil cell up $30\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. From experiments, we deduced that MC becomes gradually more symmetric pressure, transforming into one at $19.4\ifmmode\pm\else\textpm\fi{}0.5\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. This occurs without any volume change. measurements confirmed occurrence monoclinic-to-tetragonal transformation. nondegenerate modes phase, especially ${A}_{g}^{4}$ modes, exhibit negative coefficient, converging with ${B}_{g}^{1}$ becoming an $Eg$ mode experimental results are interpreted through density-functional theory (DFT) electronic-structure total-energy calculations, which showed beyond $18\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ is most stable It also shown along continuous change from InSe, there progressive decrease band gap eventually, small overlap. However, Raman-effect optical-absorption suggest this overlap probably due usual DFT band-gap underestimation. Tetragonal likely low-gap semiconductor. bonding compared.