6533b855fe1ef96bd12afd5c

RESEARCH PRODUCT

Pressure and temperature dependence of the lattice dynamics ofCuAlO2investigated by Raman scattering experiments andab initiocalculations

subject

description

We have studied the vibrational properties of $\mathrm{Cu}\mathrm{Al}{\mathrm{O}}_{2}$ 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 ${\ensuremath{\sigma}}_{{E}_{g}}=418.1\ifmmode\pm\else\textpm\fi{}0.2\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ and ${\ensuremath{\sigma}}_{{A}_{1g}}=767.2\ifmmode\pm\else\textpm\fi{}0.3\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$. Polarized measurements with single crystals have confirmed their symmetry. We present and discuss the phonon-dispersion curves. Below $200\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the temperature dependence of the Raman active modes is almost linear, with coefficients $\ensuremath{\partial}{\ensuremath{\sigma}}_{{E}_{g}}∕\ensuremath{\partial}T=(\ensuremath{-}4\ifmmode\pm\else\textpm\fi{}1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}∕\mathrm{K}$ and $\ensuremath{\partial}{\ensuremath{\sigma}}_{{A}_{1g}}∕\ensuremath{\partial}T=(\ensuremath{-}1.0\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}∕\mathrm{K}$. Most of the temperature shift is associated with thermal expansion. The pressure dependence is given by $\ensuremath{\partial}{\ensuremath{\sigma}}_{{E}_{g}}∕\ensuremath{\partial}P=2.72\ifmmode\pm\else\textpm\fi{}0.07\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}∕\mathrm{GPa}$ and $\ensuremath{\partial}{\ensuremath{\sigma}}_{{A}_{1g}}∕\ensuremath{\partial}P=4.96\ifmmode\pm\else\textpm\fi{}0.12\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}∕\mathrm{GPa}$. We observe a reversible phase transition at $34\ifmmode\pm\else\textpm\fi{}2\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, which, as already has been shown to happen in $\mathrm{Cu}\mathrm{Ga}{\mathrm{O}}_{2}$, we relate to the existence of a dynamical instability.