Structural analysis of pressure-amorphized zirconium tungstate

The negative thermal-expansion material zirconium tungstate, when subjected to a moderate pressure of 2 GPa, turns amorphous irreversibly; the amorphous state being similar to 26% more dense than the crystalline phase alpha-Zr(WO4)(2). Structure of pressure-amorphized Zr(WO4)(2) is investigated using synchrotron x-ray diffraction. Structure factors S(q) of samples recovered from different pressures are obtained. The first peak in S(q) for 10.5 GPa-treated sample is found to occur at a slightly larger q than that recovered from 5.5 GPa, suggesting that the amorphous samples recovered from higher pressure could be more dense. The pair-correlation functions g(r), obtained by Fourier transforming S(q), suggests that the further densification of amorphous phase occurs via contraction of second and third neighbor shells representing O-O and W-W and W-Zr distances rather than first neighbor shell. In contrast to earlier speculations, the present results do not show evidence for an increase in the coordination number and consequent existence of distinct amorphous phases in samples recovered from pressures up to 10.5 GPa.