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

摘要

We correlate here the specific heat C_p with the frequency shifts (1/V) (partial deriv V/partial deriv T)_p and the thermal expansivity α_p with the (1/ν) (partial deriv V/partial deriv P)_T close to the I—II transition in NH4Br. This correlation is performed for the Raman mode of ν_s (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.