Pressure and temperature dependence of the lattice dynamics of CuAlO2 investigated by Raman scattering experiments and ab initio calculations

We have studied the vibrational properties of CuAlO2 by means of Raman scattering in ambient conditions, at low temperature, and also at high pressure. Results are discussed in the framework of an ab initio calculation. Raman active modes have wave numbers sigma(Eg)=418.1 +/- 0.2 cm(-1) and sigma(A1g)=767.2 +/- 0.3 cm(-1). Polarized measurements with single crystals have confirmed their symmetry. We present and discuss the phonon-dispersion curves. Below 200 K, the temperature dependence of the Raman active modes is almost linear, with coefficients partial derivative sigma(Eg)/partial derivative T=(-4 +/- 1)x10(-3) cm(-1)/K and partial derivative sigma(A1g)/partial derivative T=(-1.0 +/- 0.2)x10(-2) cm(-1)/K. Most of the temperature shift is associated with thermal expansion. The pressure dependence is given by partial derivative sigma(Eg)/partial derivative P=2.72 +/- 0.07 cm(-1)/GPa and partial derivative sigma(A1g)/partial derivative P=4.96 +/- 0.12 cm(-1)/GPa. We observe a reversible phase transition at 34 +/- 2 GPa, which, as already has been shown to happen in CuGaO2, we relate to the existence of a dynamical instability.