Structural transitions and electron transfer in coffinite, USiO4, at high pressure

The compressibility, phase stability, and vibrational properties of coffinite (USiO4) were studied by in Situ X-ray diffraction and infrared (IR) measurements at high pressures. An irreversible phase transition from the zircon-type to scheelite-type structure was found to Occur at 14-17 GPa. Accompanying the structural transition, partial amorphization was also evident in the XRD analysis. The predicted transition pressure calculated by density functional theory is in good agreement with the experimental results. IR spectra also suggest that water is incorporated into the coffinite structure, and a pressure-induced electron transfer (U4+ -> U5+) may also occur.