Electrocaloric (EC) effect is the change in entropy and, consequently, in temperature of a dielectric material due to the electric-field-induced changes in the polar states. The (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-100xPT) ceramics of selected compositions are expected to exhibit a large EC effect due to their excellent dielectric properties, such as high dielectric permittivity and polarization, and a large change of polarization with temperature. We prepared the PMN-10PT and PMN-30PT bulk ceramics with similar densities and different grain sizes by changing the sintering temperature and time and analysed their phase composition, microstructure, dielectric and EC properties. The highest measured EC temperature change for the PMN-10PT ceramic with 3.6 m grains was 3.45 °C at 127 °C and 160 kV/cm, which is the highest reported value until now for Pb-based perovskites. The influence of the grain size on the dielectric and EC properties of PMN-10PT will be discussed in the contribution. Furthermore, we explore utilization of PMN-10PT ceramics as active elements in an EC cooling device. The experimental testing of the cooling device demonstrates the efficient regeneration and establishment of the temperature span between the hot and the cold sides of the regenerator, exceeding several times the EC temperature change of a single PMN-10PT ceramic plate.
B.04 Guest lecture
COBISS.SI-ID: 29445415This international patent application introduces the new and efficient method for the utilization of the electrocaloric effect in refrigeration, heat pumping and the power generation.
F.32 International patent
COBISS.SI-ID: 29642791The electrocaloric (EC) effect is a conversion of electrical energy to heat and may be defined as an adiabatic temperature change that occurs in a polar material upon application of an external electric field. The possibility to employ the EC materials in solid-state cooling applications has been one of the main driving forces for numerous studies, especially after 2006, when Mischenko et al. reported the giant EC temperature change ΔTEC of 12 °C at 480 kV/cm and 220 °C in PbZr0.95Ti0.05O3 thin films. Surprisingly, the efficiency of EC materials, or prototype devices has been discussed only in a few studies, although it is of the utmost importance for applications. In this work, we investigate the energy efficiency of an EC cooling system in view of the effect of the polarization-electric field P-E hysteresis losses of the EC material, and we also take into account the electric-energy recovery and heat regeneration. For the purposes of the analysis, the (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-100xPT) with x = 0, 0.1 and 0.35 ceramics were studied. PMN is considered as a prototype relaxor material while the compositions with a large PT content such as PMN-35PT behave as ferroelectrics. In the contribution we show that if no electric energy-recovery and no heat regeneration are performed on the EC cooling system, the energy efficiency of the system (ξ) does not exceed ~4 % of the efficiency of a Carnot heat pump, irrespective the PMN-100xPT composition. However, if realistic 80 % of the available electric energy is recovered, the ξ is 2.4 %, 9.4 % and 15.8 % for the PMN-35PT, PMN-10PT and PMN, respectively. The poor energy-efficiency in the case of PMN-35PT is a consequence of large P-E hysteresis losses originating from the material’s ferroelectric character. In contrast, PMN is a relaxor material with low hysteresis losses, meaning that a high degree of the electric energy can be recovered, and consequently, a high energy-efficiency can be achieved. Furthermore, we show that if both, the electric-energy recovery (80 %) and the heat regeneration are performed, the EC cooling system employing PMN as an EC working body can achieve the ξ as high as 81 %. Therefore, a high degree of the electric-energy recovery, preferably combined with a heat regeneration process, is needed to create the basis for an efficient EC cooling system.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 29768743