On taking into account the irreversibility of first-order phase transitions

Based on the fact of irreversibility of the real first-order phase transition (PT-1), an inequality was obtained that generalizes the Clapeyron–Clausius equation (CCE) in the case of irreversibility of PT-1: the Clapeyron–Clausius inequality. It was shown that the CCE determines only the maximum possible slope of the line PT-1 in the coordinates temperature–pressure and temperature–intensity of an external homogeneous magnetic (or electric) field. Analysis of experimental data for various types of PT-1 has shown that the deviation from the CCE is more noticeable the more jump in volume or jump in magnetization (or polarization) at PT-1.