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

Abstract

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 C _p(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.