Post-PbCl2 phase transformation of TeO2 -: art. no. 092101

Phase transformations of TeO2 have been investigated up to 150 GPa by x-ray diffraction and Raman scattering techniques using a diamond-anvil cell. It is found that the paratellurite phase transforms to the PbCl2 structure with a coordination number of 9, which is the maximum number so far reported in dioxide, at pressures of about 20-30 GPa. A further transformation to a post-PbCl2 phase has been observed for the first time in dioxides at pressures of about 80-100 GPa. The x-ray diffraction pattern of the post-PbCl2 phase of TeO2 could not be explained by assuming the post-PbCl2 structures reported in dihalides such as the Co2Si and Ni2In structures, and the nature of this phase has not yet been clarified. The PbCl2 phase of TeO2 contracted rather isotropically with increasing pressure similar to other dioxides, in marked contrast with the anisotropic contraction of the PbCl2 phases of dihalides. These results suggest that the mechanism of the post-PbCl2 phase transformation in dioxides may be different from that in dihalides.