Pressure-induced amorphization of cubicZrW2O8studiedin situandex situby synchrotron x-ray diffraction and absorption

The behavior of cubic $\mathrm{Zr}{\mathrm{W}}_{2}{\mathrm{O}}_{8}$ on compression in a DAC to $7.6\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ was examined in situ by a combination of synchrotron x-ray diffraction and x-ray absorption spectroscopy (XAS). These data were compared with x-ray absorption measurements on an amorphous sample of $\mathrm{Zr}{\mathrm{W}}_{2}{\mathrm{O}}_{8}$ recovered from $7.5\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ in a multianvil apparatus. The in situ diffraction data show the complete formation of orthorhombic $\mathrm{Zr}{\mathrm{W}}_{2}{\mathrm{O}}_{8}$ at low pressure $(<0.5\phantom{\rule{0.3em}{0ex}}\mathrm{GPa})$, and amorphization onset at $>2.4\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ with completion at $<7.6\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. The corresponding in situ XAS data suggest a continuous evolution of the local tungsten coordination environment on compression after forming the orthorhombic phase, with the average $\mathrm{W}\mathrm{O}$ bond length increasing, indicating an increase in the average coordination number, and the W ${L}_{I}$ pre-edge peak decreasing in magnitude, indicating a movement toward tungsten coordination that is closer to centrosymmetric These observations are inconsistent with a model for the amorphization that simply involves a loss of orientational/positional order among existing coordination polyhedra. The XANES data for the amorphous sample recovered from the multianvil apparatus are unlike any of the XANES seen in the in situ measurements, suggesting that the local structure in the glassy material relaxes on decompression. The XANES for the recovered sample are very similar to those for ammonium paratungstate, a material that contains tungsten in a variety of heavily distorted octahedral environments.