Frequency shifts of the disorder-induced modes close to the tricritical phase transition in NH4Cl
Hamit Yurtseven, D Kayisoglu
We have studied the Raman frequencies of the disorder-induced modes of ν7 (93 cm-1) and ν5 (144 cm-1) close to the tricritical phase transition in NH4Cl (P ≅ 1.6 kbar, Tc257 ≅ K). Using our observed Raman data for these phonon modes, we have obtained the value of the exponent a ≅ 0.3 for the frequency shifts, which can describe the critical behaviour of the thermal expansivity αp and also of the specific heat Cp. Our exponent value can be compared with the value of 0.1 predicted by the 3d Ising model.