High Pressure and Temperature Equation of State of NiO up to 8 GPa and 1400K

P-V-T measurements of nickel oxide (NiO) were conducted by using in situ synchrotron x-ray diffraction and a multi-anvil apparatus at the National Synchrotron Light Source. Data were collected at pressures and temperatures up to 8 GPa and 1370K. Fitting the experimental data to the third-order Birch-Murnaghan equation of state yields a bulk modulus K0=203 ± 4 GPa at a fixed K'= 4. Temperature derivative of bulk modulus is derived (∂K/∂T)P = -0.05 GPa/K for the temperature range below Néel temperature of NiO (523K), with hexagonal structure, and (∂K/∂T)P = -0.07 GPa/K for the temperature range above Néel temperature, with B1 structure. Using the values of bulk moduli above Néel temperature, we extrapolate the bulk modulus for B1 structure to ambient temperature, K0(B1) = 211 GPa. While the measured bulk modulus (K0=203 GPa) of NiO is far off the linear trend of bulk modulus of transition metal oxides (all with B1 structure) as a function of their unit cell volume, the extrapolated bulk modulus for B1 structure at ambient temperature matches the linear trend very well.