ISOMORPHIC PHASE TRANSITIONS AND OVERCRITICAL BEHAVIOR OF FERROELECTRIC CRYSTALS

摘要

Heat capacity and dielectric perminttivity data for (CH_3NH_3)_5Bi_2Hal_11(hal=Cl,Br) and rare-earth molybdate crystals reveal additional anomalies associated with the presence of a line of isomorphic phase transitions in the phase diagram. This line results from the strong nonlinearity of the equation of state of these ferroelectric crystals, as demonstrated by the sixth- and higher order expansions of the thermodynamic potential.