Study of the physical properties and electrocaloric effect in the BaTiO$_{3}$ nano- and microceramics

The specific heat, thermal expansion, permittivity, and electrocaloric effect in bulk of BaTiO$_{3}$ (BT) samples in the form of nano- (nBT-500 nm) and micro- (mBT-1200 nm) ceramics fabricated using spark plasma sintering and solid-state plasma techniques have been investigated. The size effect has been reflected, to a great extent, in the suppression of the specific heat and thermal expansion anomalies and in the changes in the temperatures and entropies of phase transitions and permittivity, and a decrease in the maximum intensive electrocaloric effect: $\Delta T^{\operatorname{max}}_{\operatorname{AD}}$ = 29 mK ($E$ = 2.0 kV/cm) for nBT and $\Delta T^{\operatorname{max}}_{\operatorname{AD}}$ = 70 mK ($E$ = 2.5 kV/cm) for mBT. The conductivity growth at temperatures above 360 K leads to the significant irreversible heating of the samples due to the Joule heat release in the applied electric field, which dominates over the electrocaloric effect.