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

摘要

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, K'_0, fixed at 4.0, we obtained the ambient bulk modulus K_0=31.5±0.7 GPa, the temperature derivative of bulk modulus at constant pressure (dK/dT)_P=-2.7 × 10~(-2) GPa/K, the volumetric thermal expansivities α_T(K~(-1))=9.8 ± 0.71 × 10~(-5)+12.62 ± 1.09 × 10~(-8) T at atmospheric pressure and α_T(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 (dα/dP)_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 (dK_T/dT)_P and (dα/dP)_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.