ИСТИНА

The heat capacity of a ferroelectric crystal in a wide temperature range can be represented as the sum of the anomalous and background specific heats. Anomalous or excess is called the part of the specific heat, which depends on the phase transition parameter and its derivatives. This part of the heat capacity is not observed if measurements are taken at a fixed value of the phase transition parameter. The background heat capacity of a crystal is the sum of its lattice heat capacity and other contributions that do not depend on the derivatives of the phase transition parameter, for example, the contribution to the heat capacity of thermal expansion. Calculation of the background heat capacity is a necessary stage in the interpretation of the experimental data on the temperature dependence of the heat capacity for ferroelectric crystals. Since the background specific heat of a crystal is substantially determined by its lattice heat capacity, the determination of the background specific heat from the experimental temperature dependence of the heat capacity of the crystal makes it possible to obtain independent information on its phonon spectrum. Conversely, the existing data on the phonon spectrum of the crystal make it easier to determination its background specific heat. Calculation of the background specific heat is quite facilitated in the presence of a sufficiently detailed temperature dependence of the heat capacity over a wide temperature interval including the ferroelectric phase transition. Obtaining such the dependences requires special thorough when planning and making a calorimetric experiment. We made a comparative review of various methods for determining the background specific heat of ferroelectric crystals. The experimental and computational approaches are analyzed using examples of such model ferroelectrics as triglycine sulfate, potassium dihydrophosphate, barium titanate and gadolinium molybdate. Also detailed are the results relating to prospective for applications crystals of lanthanum borogermanate and solid solutions based on lead titanate magnoniobate. The specificity of ferroelectric crystals is that, as a rule, in their phonon spectrum the most active are one or several polar optical modes being discussed. This circumstance can be used both in constructing the lattice specific heat from data on the phonon spectrum of the ferroelectric crystal, and in constructing the interpolation schemes necessary for interpretation the temperature dependencies of the heat capacity of ferroelectrics.