New high-pressure phase ofZrO2above 35 GPa

Phase transformations of pure ${\mathrm{ZrO}}_2$ at high pressure up to 60 GPa were investigated by using x-ray diffraction and micro-Raman-scattering methods. The existence of phase transformation at about 13 GPa was reconfirmed by the spectral change of in situ Raman scattering. A new phase transformation at 35 GPa was observed from both of the experimental methods employed. A new high-pressure phase is stable up to 60 GPa and quenchable to ambient conditions. The measured x-ray diffraction pattern for this high-pressure phase was indexed on the basis of tetragonal symmetry. Eight Raman bands were observed for the quenched high-pressure phase. Candidate space groups that are consistent with the obtained experimental results were deduced. The most plausible space group is considered as one of ${\mathit{C}}_{4\mathit{h}}^1$, ${\mathit{C}}_{4\mathit{h}}^4$, ${\mathit{D}}_{4\mathit{h}}^1$, or ${\mathit{D}}_{4\mathit{h}}^5$ (P4/m, ${\mathrm{P}4\mathrm{}}_2$/n, P4/mmm, or P4/mbm). The molar volume for the new high-pressure phase is smallest in the high-pressure phases so far reported for ${\mathrm{ZrO}}_2$. .AE