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.

The results of measurements by the ac heater-probe method of the specific heat and thermal conductivity of polycrystalline BaTiO3 films with thickness between 1 and 0.1 μm in a temperature range 120–440 K are presented. In the heating and cooling runs, the phase transition anomalies of the thermal properties in the region of each phase transition in the sequence of symmetry change m3m-4mm-mm2-3m have been observed. A temperature hysteresis is observed, which is the signature of the first order phase transitions. As film thickness decreases, anomalies shift to lower temperatures and became smeared.

Abstract. Thermal properties -specific heat and heat conductivity coefficient -of polycrystalline BaTiO 3 films on massive substrates were studied as a function of the temperature and the film thickness by ac-hot probe method. The anomalies of specific heat with decreasing of the film thickness from 1100 to 20 nm revealed the reducing of T c and excess entropy of the ferroelectric phase transition, which becomes diffused.The critical thickness of the film at which T c = 0 estimated as 2.5 nm.

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