Calculation of the P-T phase diagram of nitrogen using a mean field model

Abstract

The P-T phase diagram is calculated at low and moderate pressures by obtaining the phase line equations for the transitions considered in nitrogen using the Landau phenomenological model. For some transitions, a quadratic coupling between the order parameters is taken into account in the expansion of free energies in terms of the order parameters. A quadratic function in T and P is fitted to the experimental P-T data from the literature and the fitted parameters are determined. It is shown that the model studied here describes the observed data adequately, which can also be used to predict the thermodynamic properties of the phases of the molecular nitrogen within the temperatures and pressures of the P-T phase diagram of this system.