Pressure dependence of the RamanA1mode and pressure-induced phase transition inCuInSe2

The pressure dependence of the Raman ${\mathit{A}}_1$ mode of ${\mathrm{CuInSe}}_2$ has been studied up to 6.9 GPa in a gasketed diamond-anvil cell and the Grüneisen parameter of the optical phonon ${\mathit{A}}_1$ has been measured. From changes in the Raman spectra of the samples under pressure, a first-order phase transition, from the chalcopyrite to the disordered rocksalt structure, was observed at 7.1 GPa. In the downstroke the high-pressure NaCl-type phase of ${\mathrm{CuInSe}}_2$ reverts to a polycrystalline chalcopyrite structure at 4.2 GPa. After the phase transition, the Raman studies performed on the pressure-quenched samples show that the sample is disordered and microcrystalline.