Pressure-induced amorphization of cubic ZrMo2O8 studied in situ by X-ray absorption spectroscopy and diffraction

A combination of in situ high-pressure X-ray diffraction and Mo K-edge XANES was used to examine the changes in local structure that occur as the negative thermal expansion material cubic zirconium molybdate becomes amorphous on compression and, hence, provide insight into the mechanism of amorphization. Amorphization started at ∼1.7 and by 4.1 GPa the sample was glass like by diffraction. The XANES data shows that the pressure induced amorphization at 4.1 GPa does not involve a complete change of molybdenum coordination from tetrahedral, in the starting phase, to approximately octahedral as would be expected if the amorphous material were a metastable intermediate well advanced along the pathway towards decomposition into a mixture of MoO3 and ZrO2. Recrystallization of the amorphous material at 600 °C and 4.1 GPa produced a sample that was not a simple mixture of known MoO3 and ZrO2 polymorphs nor a known polymorph of ZrMo2O8.