Raman spectroscopy of CuAlS2 and CuAlSe2 at high pressures

The pressure dependence of the Raman-active phonons of CuAlS₂ and CuAlSe₂ single crystals has been studied up to 30 GPa in a membrane diamond anvill cell (MDAC) using nitrogen and neon gas, respectively, as pressure transmitting medium. The effect of pressure on the phonon frequencies is discussed in terms of the Grüneisen parameters. From changes in the Raman spectra of the samples under pressure, a first-order phase transition was observed at about 16 GPa (CuA1S₂) and 12 GPa (CuAlSe₂). After the phase transition, the Raman studies performed on the downstroke show that the recovered phase is disordered and the samples are microcrystallines.