To investigate the pressure-induced structural transitions of chromium dioxide (CrO$_{ 2}$), phonon dispersions and total energy band structures are calculated as a function of pressure. The first structural transition has been confirmed at P$\approx$ 10 GPa from the ground state tetragonal CrO$_{ 2}$ (t-CrO$_{ 2}$) of rutile type to orthorhombic CrO$_{ 2}$ (o-CrO$_{ 2}$) of CaCl$_{ 2}$ type. The half-metallic property is found to be preserved in o-CrO$_{ 2}$. The softening of Raman-active B$_{ 1g}$ phonon mode, which is responsible for this structural transition, is demonstrated. The second structural transition is found to occur for P$\geq$ 61.1 GPa from ferromagnetic (FM) o-CrO$_{ 2}$ to nonmagnetic (NM) monoclinic CrO$_{ 2}$ (m-CrO$_{ 2}$) of MoO$_{ 2}$ type, which is related to the softening mode at { \bf q} = R(1/2,0,1/2). The third structural transition has been newly identified at P= 88.8 GPa from m-CrO$_{ 2}$ to cubic CrO$_{ 2}$ of CaF$_{ 2}$ type that is a FM insulator.
Categories: cond-mat.mtrl-sci cond-mat.other