Variations in thermal properties of diamond under isothermal compression

Abstract

State equation P(V/V 0, T) and baric dependences of thermal properties of diamond have been obtained without any fitting parameters from the interatomic pair Mie–Lennard-Jones potential and the Einstein model of a crystal. Calculations have been performed along two isotherms (at T = 300 and 3000 K) up to P = 10000 kbar = 1000 GPa, i.e., to a relative volume of V/V 0 = 0.5. The baric dependences have been obtained for the following characteristics: isothermal elastic modulus B T and B'(P), isochoric heat capacity C v and C v ' (P), isobaric heat capacity C p ; thermal expansion coefficient α p and α p ' (P); and specific surface energy σ, as well as its derivatives σ'(P) and σ'(T). It is shown that for P → ∞, functions B T (P) and σ(P) vary linearly, functions B'(P), α p (P), C v (P), C p (P) and σ'(P) tend to constants, while functions α p '(P), C v '(P), and difference C p (P)–C v (P) tend to zero. Good agreement with experimental data has been demonstrated.