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The statistics of ferroelectrics of the KDP family is investigated on the basis of Blinc and Svetina's model. Tables and graphes for various thermodynamic quantities connected with the transition are presented which permit a comparison with the experiment and an estimation of parameters of the theory for any crystal of the family. An attempt of such a fit of parameters is made and gives a satisfactory description of all the experimental data except the differences between the Curie and Curie‐Weiss temperatures which are too small in the theory. Some trends in variations of the found parameters with composition are observed and discussed.

Specific heat of polycrystalline BaTiO 3 thin films on the fused quartz substrate was measured by ac-hot probe method. Phase transition temperature, excess entropy and spontaneous polarization were determined as a function of film thickness and grain size. The variation of the latter was obtained in the limits 30 -150 nm by changing of the temperature of the substrate during sputtering while thickness of films 20 -1100 nm was controlled by the conditions of sputtering. It was found that the relation between the thickness and grain size is important for the size effects in polycrystalline films.

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