Electrocaloric Study Effect in the Relaxor Ferroelectric Ceramic 0.9(0.75PMN-0.25PT)-0.1PS (original) (raw)
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Study of the Electrocaloric Effect in the Relaxor Ferroelectric Ceramic 0.75PMN-0.25PT
Journal of Electronic Materials, 2015
Electrocaloric (EC) cooling based on the ability of materials to change temperature by applying an electric field under adiabatic conditions is a relatively new and challenging direction in ferroelectrics research. Analytical and simulation data for the electrocaloric effect (ECE) in 0.75Pb(Mg 1/3 Nb 2/3)O 3-0.25PbTiO 3 (0.75PMN-0.25PT) bulk ceramic samples are reported. The adiabatic temperature change (DT) due to a change of the external electric field has been calculated indirectly from the entropy change. The temperature change increases with an increase in the applied electric field and reaches a maximum of 2.1 K in 25 kV/cm electric field shift near the Curie temperature of 398 K; that is, the cooling DT per unit field (MV/m) is 0.896 9 10 À6 m K/V. This value is significantly large for bulk ceramics and makes the compound promising for room-temperature electric cooling applications.
Lead-free Relaxor Ferroelectrics for Electrocaloric Cooling
Materials Today: Proceedings, 2016
In this work, we consider electrocaloric (EC) device operation at high electric fields E above the temperature Tm of the maximum dielectric permittivity. Here, the EC response is determined by the temperature dependence of dielectric permittivity while dielectric losses are comparably low. We discuss materials selection and EC device concepts. An upper bound of the EC effectindependent on phase transition-is proposed which is based on the maximum energy density storable in a dielectric. Relaxors promising for EC applications are discussed.
2012
The electrocaloric (EC) effect accompanied with the ferroelectric to paraelectric phase transition in (111)-oriented PbMg 1/3 Nb 2/3 O 3 (PMN) is investigated. It is shown that the largest change T is 0.37 K in 3 kV/cm electric field shift near the Curie temperature of 221 K; that is, the cooling T per unit field (MV/m) is 1.23×10 6 m•K/V. This value is significantly larger, and comparable with the value of 0.254×10 6 m•K/V for PbZr 0.95 Ti 0.05 O 3 thin film under larger electric field shift E = 30 kV/cm. Thus, the EC effect of (111) PMN single crystal provides cooling solutions at low temperatures, and opens more opportunities for practical application in cooling systems.
Applied Physics Letters, 2006
We have recently observed a giant electrocaloric effect (12 K in 25 V) in 350 nm sol-gel PbZr0.95Ti0.05O3 films near the ferroelectric Curie temperature of 242 • C. Here we demonstrate a giant electrocaloric effect (5 K in 25 V) in 260 nm sol-gel films of the relaxor ferroelectric 0.9 PbMg 1/3 Nb 2/3 O3-0.1 PbTiO3 near the Curie temperature of 60 • C. This reduction in operating temperature widens the potential for applications in novel cooling systems.
Electrocaloric properties of high dielectric constant ferroelectric ceramics
Journal of the European Ceramic Society, 2007
In the last two decades, the electrocaloric (EC) effect which is associated to the temperature (θ) dependence of the macroscopic polarization P(E, θ) under electric field E has been spasmodically studied in ferroelectric materials in order to find an alternative to the classical refrigeratory devices using freon. Basically, large electrocaloric temperature variation T originates from electric field-induced phase transition at the Curie temperature, but temperature changes of the sample are difficult to measure and depend on the experimental conditions. In this paper, the electrocaloric effect has been quantified directly and precisely by measuring the thermal energy exchanged under isothermal conditions using a modified Differential Scanning Calorimetry (DSC) apparatus. The DSC technique allowed to compare the EC properties of high-dielectric-constant (ε) ceramics in the vicinity of ferroelectric-paraelectric phase transition. The measurements were also simulated starting from polarization versus electric field hysteresis loops for different temperatures. It is shown excellent agreement between simulations and direct DSC measurements, except in a limited temperature range where the hysteresis of the polarization versus temperature is high.
Electrocaloric Effect In Relaxor Ferroelectric Ceramics and Single Crystals
2006 IEEE International Symposium on the Applications of Ferroelectrics, 2006
The electrocaloric effect (ECE) in normal and relaxor ferroelectrics is investigated in the framework of a thermodynamic approach based on the Maxwell relation and a Landau-type free energy model. The static dielectric response of relaxors is described by the spherical random bond-random field model, yielding the first Landau coefficient a = a(T ), which differs from the usual expression for ferroelectrics. The fourth-order coefficient b is treated as a phenomenological parameter, which is either positive or negative due to the anisotropy of the stress-mediated coupling between the polar nanoregions. When b < 0, the maximum ECE in a relaxor is predicted near the critical point in the temperature-field phase diagram, whereas in a ferroelectric it occurs at the first order phase transition. The theoretical upper bound on the ECE temperature change is estimated from the values of saturated polarization, effective Curie constant, and specific heat of the material.
Based on the experimental data of the isothermal polarization P(T,E) of BaHf 0.11 Ti 0.89 O 3 bulk ceramic, entropy change (∆S), temperature change (∆T), and heat carrying capacity (∆Q) of the material are evaluated in detail using an artificial neural network (ANN) procedure. As a result, the maximum ECE occurs above T C and shifts to higher temperatures with increasing applied field. The BaHf 0.11 Ti 0.89 O 3 ceramic exhibits large ECE parameters around the Curie temperature (T C) associated with a relatively broad electrocaloric temperature span. Furthermore, under different electric fields, many figures of merit such as relative cooling power, temperature-averaged entropy change, and normalized refrigerant capacity are explored, making the sample a promising material for green cooling devices. Such figures of merit increase monotonically with the enhancement of the applied field. In addition, the field dependence of the ∆S and ∆T is thoroughly investigated. The master curve and the exponent n controlling the field dependence of both magnitudes confirm the second-order character of the electric phase transition of the sample. The ANN method provides very accurate and fast predictions with a small amount of experimental data. Therefore, this method accelerates the characterization of novel electrocaloric materials by shortening the time necessary for experimentation.
Temperature hysteresis of the capacitance dependence C"T… for ferroelectric ceramics
The influence of applied electric field, temperature variation rate, and free charge carrier density on the hysteresis of C͑T͒ dependence is investigated on ferroelectric ceramic capacitors. The measurements were performed on the ceramic capacitors of Ba 0.55 Sr 0.45 TiO 3 containing 12 wt % of Mg complex additive and the 0.87Pb͑Mg 1/3 Nb 2/3 ͒O 3 -0.13PbTiO 3 ceramics. The investigations were directed to study of electrocaloric response of ferroelectric ceramics. Various mechanisms of temperature hysteresis are discussed.