λ‐transition of NH4Cl and ND4Cl at high pressures

Abstract

AbstractWe predict in this study using the mean‐field theory, the phase‐line equation from the free energy expanded in terms of the order parameters of solid II and III phases of NH4Cl and ND4Cl close to the λ‐phase transitions at high pressures. Using the temperature and pressure dependence of the coefficients given in the phase‐line equation, it is shown that the experimentally observed T –P phase diagram for the solid II–solid III transition, can be predicted from the mean field model studied here for both crystalline structures. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)