Electrocaloric, energy storage and dielectric properties of lead-free Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃ ceramic prepared by hydrothermal-assisted sintering technique

In this work, lead-free calcium barium zirconium titanate ceramic of the composition Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃ (denoted BCZT) were elaborated hydrothermally at low temperature and sintered at 1400 °C for 8 h. In bulk ceramic, a significant electrocaloric effect and high energy storage were obtained by reducing the thickness of the ceramic. Structural, dielectric, electrocaloric and energy storage properties were studied for BCZT ceramic. The Rietveld refinement technique in conjunction with X-ray diffraction analysis verified the formation of a biphasic perovskite structure, characterized by the coexistence of tetragonal (P4mm) and orthorhombic (Pmm2) phases at room temperature, without the presence of foreign phases. The texture and homogeneous microstructure were examined by scanning electron microscopy (SEM), showing that the ceramic grains have a uniform distribution with an average size of 34.85 μm and a dense morphology due to the high sintering temperature. An impedance spectroscopy study of dielectric measurements over a frequency range from 1 kHz to 1 MHz and a temperature range from 15 to 100 °C revealed a maximum dielectric constant (ε_rmax) of 14,516 at around 66 °C, associated with a ferroelectric-paraelectric phase transition. The adiabatic variation of the electrocaloric temperature (ΔT) and the reactivity (ζ) were indirectly determined by the Maxwell approach and the measured ferroelectric polarization P(T, E) extracted from the P-E hysteresis loops. The energy storage density (W_total) was also modelled using Landau-Ginzburg-Devonshire (LGD) phenomenological theory.