Critical behaviour of the specific heat calculated using the Raman frequencies of the lattice and internal modes near the λ-phase transition in NH4Br

The specific heat which we calculate here using our frequencies of both Raman modes, agrees well with the observed specific heat CP near the λ-phase transition in NH4Br. Some discrepancy occurring in the specific heat above Tλ due to the lattice mode is explained within the framework of an Ising pseudospin-phonon coupled model for NH4Br.