Heat capacity of nanocrystalline bismuth ferrite

The heat capacity of the nanocrystalline multiferroic $\mathrm{BiFeO}_3$ was studied in a wide temperature interval of $150$–$800$ K. It was found that the heat capacity nanocrystalline of bismuth ferrite in the temperature range of $350$–$570$ K is noticeably larger than that of the microcrystalline sample. It was shown that the temperature dependence of the excess heat capacity is due to the manifestation of the Schottky effect for the three-level states appearing as a result of the structural distortions. The anomaly of the heat capacity typical for the phase transition, the manifestation of which depends on crystallite sizes, was discovered in the temperature range of $T \approx 720$–$750$ K.