Clarification of size effects in polycrystalline BaTiO3 thin films by means of the specific heat measurements: grain size or film thickness?

Specific heat of polycrystalline BaTiO3 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.