Monocrystal elastic constants of the negative-thermal-expansion compound zirconium tungstate (ZrW2O8)

We measured zirconium tungstate's elastic constants C-ij. This compound shows relatively soft, nearly isotropic elastic constants with normal Poisson ratios and no approach to Born instability. ZrW2O8 shows normal ambient-temperature elastic constants C-ij, but remarkable dC(ij)/dT that show dominant low-frequency acoustic-vibration modes. From the bulk modulus, we estimated the total ambient-temperature thermodynamic Gruneisen parameter as gamma=-1.2. The dB/dT slope gives a Gruneisen parameter gamma=-7. The 300-0 K bulk-modulus increase (40%) seems unprecedented and breaks Birch's law of corresponding states.