Electrocaloric properties of 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 ceramics Vrabelj, Marko; Ursic, Hana; Rozic, Brigita ...
2013 Joint IEEE International Symposium on Applications of Ferroelectric and Workshop on Piezoresponse Force Microscopy (ISAF/PFM),
2013-July
Conference Proceeding
The electrocaloric (EC) effect is a conversion of electrical energy to heat and may be defined as an adiabatic and reversible temperature change that occurs in a polar material upon external electric ...field. The aim of our work was to prepare 0.7Pb(Mg 1/3 Nb 2/3 )O 3 -0.3PbTiO 3 (0.7PMN-0.3PT) ceramics and to study the EC temperature change (ΔT) vs. applied electric field and temperature. For the synthesis of the 0.7PMN-0.3PT bulk ceramics, PbO, MgO, TiO 2 and Nb 2 O 5 were used. The homogenized, stoichiometric powder mixtures were mechanochemically activated in a high-energy planetary mill, and milled in an attrition mill in isopropanol. The powder compacts were sintered at 1200 °C for 2 h in double alumina crucibles in the presence of the packing powder. The ceramic was single phase perovskite, with the relative density of 97 % and a uniform microstructure with the median grain size of 1.0 μm ± 0.5 μm. In order to study the EC effect, a high resolution calorimeter was used. The observed magnitudes of the EC effect confirmed the existence of a large EC effect in this material. A characteristic peak of AT as a function of the electric field was observed near the critical point, with the AT of 2.7 K at 90 kV/cm and 430 K.
The electrocaloric effect (ECE) of 0.85PbMg
1/3
Nb
2/3
O
3-
0.15PbTiO
3
(0.85PMN-0.15PT) thin films deposited on (111) Pt/TiO
2
/SiO
2
/Si substrate by pulsed laser deposition (PLD) has been ...calculated. The reversible adiabatic temperature was calculated indirectly using the Maxwell's relation
. Permittivity and P-E measurements show an anomaly at 11°C on heating only. This anomaly previously reported are claimed to arise due to the PNR depolarization upon heating. The absence of this anomaly during cooling suggests that no structural phase transition takes place. A negative electrocaloric effect is observed which is explained by the increase in the entropy term.
We determine isothermal entropy changes ( ) associated with electrocaloric, magnetocaloric, and the corresponding multicaloric effects in a model type-I multiferroic system using Landau-Devonshire ...thermodynamic analysis. We show that (a) the magnetocaloric effect exhibits an unexpected anomaly at the ferroelectric transition occurring at a high temperature, even in the absence of magnetic ordering, and (b) the synergy between electro- and magnetocaloric effects leads to a significantly enhanced multicaloric effect ( ) over a wide temperature range when the difference in temperatures of magnetic and ferroelectric ordering ( ) is small. This result originate from the coupled thermal fluctuations of magnetic and electric order parameters. While the former is useful in detecting multiferroic materials from the measurements covering higher temperature transition alone, the latter augurs well for caloric applications of multiferroics.
In the present work we investigate the influence of acceptor (K + , Cu + , Li + ), donor (La 3+ , Bi 3+ , Eu 3+ , Nd 3+ , Y 3+ , Cr 3+ ) and charge equivalent dopants (Sr 2+ , Co 2+ , Mn 2+ , Ta 5+ ) ...on the dielectric and ferroelectric behavior of 0.92 Pb(Mg 1/3 Nb 2/3 )O 3 -0.08 PbTiO 3 (0.92PMN-0.08PT). As a criterion for the basic suitability for electrocaloric cooling application, we directly measure the temperature change (ΔT) upon the application and withdrawal of an electric field as a function of the ambient temperature. For the undoped 0.92PMN-0.08PT bulk ceramics fabricated by the columbite route, we observed the maximum ΔT of 0.24 K when applying an electric field of 2 kv-rnm -1 at 28°C (ΔT up ). Withdrawing the electric field at same conditions showed a temperature decrease of 0.20 K (ΔT down ). The resulting ΔT down :ΔT up ratio is also considered.
Direct electrocaloric measurements using a differential scanning calorimeter Sanlialp, Mehmet; Shvartsman, Vladimir V.; Lupascu, Doru C. ...
2015 Joint IEEE International Symposium on the Applications of Ferroelectric (ISAF), International Symposium on Integrated Functionalities (ISIF), and Piezoelectric Force Microscopy Workshop (PFM),
05/2015
Conference Proceeding
The electrocaloric effect (ECE) in ferroelectric materials is a promising mechanism for the development of small, effective, low cost, and environmentally friendly solid state refrigerators. During ...the last decade, an increased interest has been paid to studies of this effect. Getting reliable values requires direct measurements of the ECE instead of the frequently used indirect estimates based on Maxwell's relation. In this paper, we report on the modification of a differential scanning calorimeter for direct ECE measurements. The importance of proper estimation of the heat capacitance and thermal losses for the correct ECE measurements is discussed. The ECE was measured for bulk ceramics Ba(Zr 0.2 Ti 0.8 )O 3 . The temperature change reaches a value of ΔT EC = 0.44 K at 305 K under an electric field of 2 kV/mm. The obtained data are compared with results of the evaluation of the indirect ECE.
The effect of misfit strain on the electrocaloric effect in polydomain epitaxial BaTi03 thin films at room temper- ature is investigated using the Ginzburg~Landau Devonshire thermodynamic theory. ...Numerical calculations indicate that the misfit strain has a large impact on the ferroelectric polarization states and the electrocaloric effect. Most importantly, the electrocaloric effect in the polydomain ca1/ca2/ca1/ea2 phase is much larger than that in the mon- odomain c phase and the other polydomain phases. Consequently, a large electrocaloric effect can be obtained by carefully controlling the misfit strain, which may provide potential applications in refrigeration devices.
0.68PbMg1/3Nb2/3O3–0.32PbTiO3 (PMN–PT) thin films with a lead zirconate titanate Pb(Zr0.3Ti0.7)O3 (PZT)/PbOx buffer layer were deposited on Pt/TiO2/SiO2/Si substrates by radio frequency magnetron ...sputtering technique, and pure perovskite crystalline phase with highly (100)-preferred orientation was formed in the ferroelectric films. We found that the highly (100)-oriented thin films possess not only excellent dielectric and ferroelectric properties but also a large electrocaloric effect (13.4K at 15V, i.e., 0.89K/V) which is attributed to the large electric field-induced polarization and entropy change during the ferroelectric–paraelectric phase transition. The experimental results indicate that the use of PZT/PbOx buffer layer can induce the crystal orientation and phase purity of the PMN–PT thin films, and consequently enhance their electrical properties.
(001)-oriented 0.67PbMg1/3Nb2/3O3–0.33PbTiO3 thin films with a pure perovskite crystalline phase were deposited on LaNiO3-coated SiO2/Si substrates by the rf magnetron sputtering technique. We found ...that the as-grown thin films with (001)-oriented texture possess not only excellent dielectric and ferroelectric properties but also a large electrocaloric effect (14.5 K in 12 V, i.e., 1.21 K/V) which is attributed to the large polarization and entropy change during the ferroelectric–paraelectric phase transition at a high electric field. The discovery of the large electrocaloric effect in highly textured ferroelectric thin films widens their potential applications, such as in solid-state electrical refrigeration.
► Highly pure (001)-oriented 0.67PMN–0.33PT thin films were grown. ► The thin film possesses excellent properties including a large electrocaloric effect. ► The large electrocaloric effect is attributed to the large polarization and entropy change. ► This discovery widens the potential applications of ferroelectric thin films.
The electrocaloric (EC) effect attracted attention due to recent predictions of the existence of a giant EC in polymeric and inorganic ferroelectric materials based on indirect measurements of the ...electric polarization. The giant EC effect could potentially be of great importance in development of cooling or heating devices of new generation, which would be more environmentally friendly. A method and analysis of direct measurements of the giant EC effect in P(VDF-TrFE) (68/32 mol%) copolymer thin films are presented. It is found that the EC effect is of similar magnitude as found in P(VDF-TrFE) (55/45 mol%) copolymer by indirect method.
Ce mémoire de thèse porte sur la caractérisation de l'effet électrocalorique des matériaux ferroélectriques solides et cristaux liquides. La découverte récente d'un effet électrocalorique qualifié de ..."géant" a relancé l'intérêt pour l'étude et la caractérisation des propriétés électrocaloriques des matériaux. Au-delà de la recherche des matériaux performants, ce domaine de recherche concerne également le développement des techniques de caractérisations appropriées et la réalisation des prototypes de réfrigération électrocalorique. Dans ce contexte, notre étude se focalise sur le développement de nouvelles techniques de caractérisation, la méthode photopyroélectrique (indirecte) et la calorimétrie (directe). La technique photopyroélectrique, développée au sein du laboratoire a été utilisée pour la détermination des propriétés thermiques du matériau pyroélectrique lui-même. L'exploitation de cette technique nous a permis également de déterminer les propriétés pyroélectriques du matériau, en particulier le rapport entre le coefficient pyroélectrique et la capacité calorifique, en fonction de la température et du champ électrique appliqué, nécessaire pour une évaluation indirecte de l'effet électrocalorique. Plusieurs matériaux ferroélectriques solides et liquides ont été étudiés à l'aide de cette méthode, en particulier, un monocristal de TriGlycine Sulfate et deux cristaux liquides. L'effet électrocalorique a été évalué autour de la température de transition de phase que présentent chacun de ces matériaux. Pour valider les résultats obtenus, nous avons procédé à des mesures indirectes de la polarisation par la méthode usuelle du courant de dépolarisation. Dans ce travail, nous avons également développé une technique de mesure indirecte de l'effet électrocalorique, par mesure calorimétrique, à l'aide d'un nouveau dispositif. Outre l'étude des transitions de phase et de la capacité calorifique, cet instrument permet une mesure directe de la température et de la quantité de chaleur absorbée ou cédée avec le milieu environnant. Une première étude de l'effet électrocalorique a été réalisée sur un matériau multicouche à base de titanate de baryum. Les résultats obtenus par cette approche ont été ensuite comparés à d'autres techniques directes et indirectes existantes dans la littérature. Ces deux nouvelles approches permettent d'élargir les possibilités d'étude de futurs matériaux électrocaloriques et de mesurer à la fois les propriétés thermiques et pyroélectriques nécessaires pour l'étude de l'effet électrocalorique.
This thesis work deals with the characterization of the electrocaloric effect in solid and liquid crystal ferroelectric materials. Following the 2006 discovery of Mischenko and al., the characterization techniques of the electrocaloric effect and the exploration of new caloric materials have attracted much attention. This discovery showed also that electrocaloric materials can be used for efficient innovative solution for refrigeration devices. This PhD dissertation focuses on the development of new techniques used to evaluate the electrocaloric effect by the photopyroelectric technique and by calorimetry. Few years ago, a new particular configuration based on the photopyroelectric technique, developed in our laboratory, was described for measuring thermal parameters of pyroelectric materials themselves. By means of this technique, we indirectly investigate the electrocaloric effect in ferroelectric materials by measuring the ratio of the pyroelectric coefficient to the volumetric heat capacity, as function of temperature and applied field, using Maxwell's relation. Measurements were carried out on ferroelectric solid materials (TriGlycine Sulfate) and liquid crystals. Electrocaloric effect has been evaluated around the phase transition temperature of each sample. To further validate the accuracy to the evaluated adiabatic temperature changes, we proceeded to indirect measurements by using the polarization reversal current technique. In the present work, we also developed a calorimeter in order to directly evaluate the electrocaloric effect. This technique is mainly used to measure with high resolution the heat capacity and enthalpy near phase transition temperature. In addition, this technique allows us to directly measure the temperature and the amount of heat absorbed or transferred from the material to the surrounding environment. A primary study of the electrocaloric effect was carried out on a multilayer material based on barium titanate. The results obtained by this approach have been then compared to conventional direct and indirect measurements. Those two new approaches give access to the measurement of both thermal and pyroelectric properties allowing the evaluation of the electrocaloric effect.