Calculation of the specific heat from the Raman frequency shifts close to the tricritical and second order phase transitions in NH4ClNH4Cl

This study gives our calculation for the specific heat using our Raman frequency shifts of the ν5(174cm-1) mode close to the tricritical (P=1.6kbar) and second order (P=2.8kbar) phase transitions in NH4ClNH4Cl. For this calculation we use as the values of the critical exponent for the specific heat, a=0.11a=0.11 (TTcT>Tc) for the tricritical (Tc=257.17K), and a=0.18a=0.18(TTc)(T>Tc) for the second order (Tc=268K) phase transitions, which we deduce from our analysis of the Raman frequency shifts of this mode studied here, on the basis of an Ising model.Our calculated specific heats agree well with those measured thermodynamically for both tricritical and second order phase transitions in NH4ClNH4Cl.