Strong electrocaloric effect in lead-free 0.65Ba(Zr0.2Ti0.8)O3-0.35(Ba0.7Ca0.3)TiO3 ceramics obtained by direct measurements

Mehmet Sanlialp (1) , V.V. Shvartsman (1) , Matias Acosta (2) , Brahim Dkhil (3) , D.C. Lupascu (2)

1 CeNIDE - Center for Nanointegration Duisburg-Essen
2 Institute of Materials Science
3 SPMS - Laboratoire Structures, Propriétés et Modélisation des solides

Strong electrocaloric effect in lead-free 0.65Ba(Zr 0.2 Ti 0.8)O 3-0.35(Ba 0.7 Ca 0.3)TiO 3 ceramics obtained by direct measurements Solid solutions of (1 À x)Ba(Zr 0.2 Ti 0.8)O 3-x(Ba 0.7 Ca 0.3)TiO 3 promise to exhibit a large electrocaloric effect (ECE), because their Curie temperature and a multiphase coexistence region lie near room temperature. We report on direct measurements of the electrocaloric effect in bulk ceramics 0.65Ba(Zr 0.2 Ti 0.8)O 3-0.35(Ba 0.7 Ca 0.3)TiO 3 using a modified differential scanning calorimeter. The adiabatic temperature change reaches a value of DT EC ¼ 0.33 K at $65 C under an electric field of 20 kV/cm. It remains sizeable in a broad temperature interval above this temperature. Direct measurements of the ECE proved that the temperature change exceeds the indirect estimates derived from Maxwell relations by about $50%. The discrepancy is attributed to the relaxor character of this material. V C 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4907774] During the last several years, an increased interest has been paid to the electrocaloric effect (ECE) in ferroelectric materials as a route to develop small, effective, low cost, and environmentally friendly solid-state refrigerators. 1,2 The ECE is defined as an adiabatic and reversible temperature change of a dielectric material when an electric field is applied or removed. 3 If the exchange of heat with the environment is enabled, it defines the change of entropy as a function of the applied electric field under isothermal conditions. 4,5 Since Mischenko et al. reported on the giant electro-caloric effect in PbZr 0.95 Ti 0.05 O 3 thin films in 2006, 6 the ECE has been reported for many different ferroelectric materials such as thick and thin films, 7–10 polymers, 11,12 bulk ceramics, 13,14 and single crystals. 15,16 In general, the ECE peaks are a few degrees above the ferroelectric-paraelectric phase transition. 1 The largest values have been achieved for thin films, 10 where much higher electric fields can be applied than to bulk materials. However, for application, the heating/ cooling capacity is the key factor. Hence, bulk materials, which have large enough heating/cooling capacity, are better suitable for mid-and large-scale cooling applications. 1 To compare the ECE in different materials, the ratio between induced temperature change and applied field, DT EC /DE, called the electrocaloric strength, has been introduced.

Domaines: Science des matériaux [cond-mat.mtrl-sci]

Mehmet Sanlialp, V.V. Shvartsman, Matias Acosta, Brahim Dkhil, D.C. Lupascu. Strong electrocaloric effect in lead-free 0.65Ba(Zr0.2Ti0.8)O3-0.35(Ba0.7Ca0.3)TiO3 ceramics obtained by direct measurements. Applied Physics Letters, 2015, 106, pp.062901. ⟨10.1063/1.4907774⟩. ⟨hal-01258574⟩