On the anomaly of the specific heat of real KH2PO4 crystals

The splitting of the anomaly revealed in the specific heat of real crystals of potassium dihydrogen phosphate KH₂PO₄ is discussed. It is demonstrated that the observed effect is characteristic of first-order phase transitions occurring near the tricritical point and originates from the specific features inherent in the defect structure of real crystals. A method is proposed for describing the experimentally observed splitting of the specific heat anomaly in the framework of the Landau theory with due regard for the possible formation of metastable states characterized by the polarization aligned antiparallel to the applied electric field in the polar phase.