Raman spectroscopic studies of the polymorphism in ZrO2 at high pressures

The Raman spectra of Zro2 at high pressures are measured at room temperature using a diamondanvil pressure-cell. Two kinds of pressure transmitting medium, methanol and Nacl, are used to see the effect of stress components on the phase transformation. The pressure of phase transformation shows a considerable difference between the two media. In the case of methanol, a phase transformation is observed at 3.5 Gpa, while in the case of Nacl, at 5.4 GPa. In the high-pressure phase, 19 Raman bands are observed. This number of bands far exceeds that which is expected for the tetragonal phase, D in space group. From the relation between the number of Raman bands and the crystal structure, it is more reasonable to consider that the high-pressure phase belongs to a orthorhombic system. The space group of the high-pressure phase is discussed on the basis of the observed number of Raman bands.