Knowledge Bank

We establish here the modified Pippard relations by relating the specific heat $Cp$ to the frequency shifts $\frac{1}{\nu }\left( {\frac{{\partial \nu }}{{\partial T}}} \right)_P $ and also the thermal expansivity $\alpha p$ to the $\frac{1}{\nu }\left( {\frac{{\partial \nu }}{{\partial P}}} \right)_T $ for the $\nu$ (140 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$) Raman mode of NH$4$Br close to its phase I- phase II transition. From our linear plots of $Cp$ vs. $\frac{1}{\nu }\left( {\frac{{\partial \nu }}{{\partial T}}} \right)_P $ and $\alpha p$ vs. $\alpha p$ to the $\frac{1}{\nu }\left( {\frac{{\partial \nu }}{{\partial P}}} \right)_T $,weextractthevaluesoftheslopeDP/dT,whichareclosetotheexperimentalvalueof28.2bar/$^irc$CnearthephaseI-phaseIItransitioninNH$_4$Br.