Pippard relations modified by the Raman frequency shifts for the phases I and II in NH4I

Linear variation of CP with the (1/ν)(∂ν/∂T)P and also a linear variation of αP with the (1/ν)(∂ν/∂P)T, indicate that the frequency shifts obtained for the ν7 (40 cm−1) lattice mode exhibit similar critical behaviour as CP and αP close to the I-II phase transition in NH4I.