Pressure-induced elastic softening of monocrystalline zirconium tungstate at 300 K

The elastic tensor of monocrystalline ZrW2O8 was determined near 300 K as a function of pressure, using pulse-echo ultrasound in a large-volume moissanite anvil cell. An unusual decrease in bulk modulus with increased pressure was observed. A framework-solid-based nonlinear model with many degrees of freedom predicts the observed behavior. We also observe that ReO3, a similar framework solid but lacking the necessary degrees of freedom, fails to display softening. Additionally, the pressure-induced phase transition from alpha-ZrW2O8 (cubic) to gamma-ZrW2O8 (orthorhombic) is found to take place at approximate to 0.5 GPa, a result confirmed by Raman spectroscopy.