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

Abstract

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±1.09×10−8T at atmospheric pressure and αT(K−1)=5.45±1.17×10−5+6.53±1.45×10−8T 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.