Thermal equations of state and melting of lithium deuteride under high pressure

Based on in situ high-pressure and high-temperature neutron diffraction experiments at pressures of up to 4.1 GPa and temperatures of up to 1280 K, thermoelastic parameters were derived by using a Birch-Murnaghan equation of state. With the pressure derivative of the bulk modulus, K0′, fixed at 4.0, we obtained the ambient bulk modulus K0 =31.5±0.7 GPa, the temperature derivative of bulk modulus at constant pressure (K/T) P =-2.7× 10-2 GPa/K, the volumetric thermal expansivities αT (K-1) =9.8±0.71× 10-5 +12.62±1.09× 10-8 T at atmospheric pressure and αT (K-1) =5.45±1.17× 10-5 +6.53±1. 45× 10-8 T at 3.0 GPa, and the pressure derivative of thermal expansion (α/P) T =-2.72× 10-5 GPa-1 K-1. Within the experimental uncertainties, the ambient bulk modulus and volumetric thermal expansion determined from this work are in good agreement with previous experimental results, whereas the derived ( KT /T) P and (α/P) T values provide the thermoelastic equation-of-state parameters for LiD. We also determined the melting temperature of LiD under high pressure. Our results reveal a substantially increased thermal stability for crystalline LiD when compared to a previous theoretical prediction that used a combined technique of two-phase simulation and first-principles molecular dynamics.