Correlations of the thermodynamic quantities with the frequency shifts of a lattice mode close to the I-II transition in NH4Br

We correlate here the specific heat Cp with the frequency shifts (1/V) (∂V/∂T)p and the thermal expansivity αp with the (1/ν) (∂V/∂P)T close to the I-II transition in NH4Br. This correlation is performed for the Raman mode of νs (140 cm−1) using the molar volume data for NH4Br. It is shown here that spectroscopic modifications of the Pippard relations are applied satisfactorily to the I-II phase transition by using a lattice mode of NH4Br.