Variations in thermal properties of diamond under isothermal compression

Abstract

State equation P(V/V₀, 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/V₀ = 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.