Elasticity of single-crystal MgO to 8 gigapascals and 1600 kelvin

The cross pressure (P) and temperature (T) dependence of the elastic moduli (C-ij) of single-crystal samples of periclase (MgO) from acoustic wave travel times was measured with ultrasonic interferometry: partial derivative(2)C(11)/partial derivative P partial derivative T = (-1.3 +/- 0.4) x 10(-3) per kelvin; partial derivative(2)C(110)/partial derivative P partial derivative T = (1.7 +/- 0.7) x 10(-3) per kelvin; and partial derivative(2)C(44)/partial derivative P partial derivative T = (-0.2 +/- 0.3) x 10(-3) per kelvin. The elastic anisotropy of MgO decreases with increasing pressure at ambient temperature, but then increases as temperature is increased at high pressure. An.assumption of zero cross pressure and temperature derivatives for the elastic moduli underestimates the elastic anisotropy and overestimates the acoustic velocities of MgO at the extrapolated high-pressure and high-temperature conditions of Earth's mantle.