Effect of γ irradiation on the structural and thermal properties of [N(C2H5)4]2ZnBr4 in the vicinity of a first-order phase transition

The unit cell parameters a and c of nonirradiated [N(C2H5)4]2ZnBr4 crystals in the temperature region 90–300 K and of samples irradiated with γ rays to doses of 106 and 5 × 106 R in the 270-to 300-K interval were measured using x-ray diffraction. The data obtained were used to derive the thermal expansion coefficients αa and αc. It is shown that the parameter a increases and the parameter c decreases with increasing temperature. In the vicinity of the phase transition (PT) at T = 285 K, the temperature dependences of a(T) and c(T) reveal anomalies in the form of jumps and the αa(T) and αc(T) curves have a maximum and a minimum, respectively. The heat capacity of nonirradiated and irradiated [N(C2H5)4]2ZnBr4 samples was measured by adiabatic calorimetry. A maximum was found in the Cp(T) curve at T = 285 K. Both x-ray diffraction and heat capacity measurements showed that the PT temperature decreased after γ irradiation.