Zirconium coordination change upon the pressure-induced amorphization of cubicZrW2O8andZrMo2O8

Abstract

Extended x-ray-absorption fine structure (EXAFS) and x-ray absorption near-edge structure (XANES) were used to examine cubic ${\text{ZrW}}_{2}{\text{O}}_{8}$ and cubic ${\text{ZrMo}}_{2}{\text{O}}_{8}$ that had been pressure amorphized at 7.5 and 5 GPa, respectively, in a multianvil press and recovered to ambient conditions. Data were taken at the $\text{W}\text{ }{\text{L}}_{\text{III}}$ and ${\text{L}}_{\text{I}}$ or $\text{Mo}\text{ }K$ edges, as well as at the $\text{Zr}\text{ }K$ edge. They indicate an increase in the average coordination number of tungsten in ${\text{ZrW}}_{2}{\text{O}}_{8}$ and a less pronounced increase in that of molybdenum in ${\text{ZrMo}}_{2}{\text{O}}_{8}$, in agreement with previous work. Notably, the $\text{Zr}\text{ }K$-edge XANES and EXAFS analyses provide strong evidence for a previously unreported change in the average Zr coordination from 6 to $\ensuremath{\sim}7$ during the amorphization of both compounds.