Effect of γ irradiation on the thermochromic phase transition in [(C2H5)2NH2]2CuCl4 crystals (as derived from heat capacity measurements)

The heat capacity of [(C2H5)2NH2]2CuCl4 crystals, both nonirradiated and γ-irradiated to a dose of 107R, was studied in the temperature interval 90–330 K by adiabatic calorimetry. The temperature dependence of Cp(T) was found to have a peak-shaped anomaly in the region of the thermochromic phase transition (PT) at T = 322.7 K. Smoothened experimental heat capacity data were used to calculate the changes in the thermodynamic functions. The changes in the entropy and enthalpy of the thermochromic PT were determined to be ΔS = 42 J K−1 mol−1 and ΔH = 13653 J mol−1 for the nonirradiated crystals and ΔS = 39 J K−1 mol−1 and ΔH = 12120 J mol−1 for the irradiated crystals, respectively. Irradiation of a [(C2H5)2NH2]2CuCl4 crystal by γ rays to a dose of 107 R was shown to shift the PT point toward lower temperatures by ΔT ≈ 1.7 K.