Calculation of the T–P phase diagram for oxygen using the mean field theory

Abstract T–P phase diagram of oxygen with the liquid and solid phases (α, ά, ᾱ, β, γ and ϵ) is calculated using the mean field theory. By expanding the free energy in terms of the order parameter, the phase line equations are derived and they are fitted to the experimental T–P data from the literature. Our calculated T–P phase diagram predicts adequately the observed behavior of the transitions between the liquid and solid phases in oxygen (O2). Some thermodynamic quantities are predicted from the free energy expansion for the liquid–γ and ά–ɛ transitions in O2.