Characterization

Poster

Direct measurements of the electrocaloric effect in BaTiO₃-based ferroelectric ceramics

Mehmet Sanlialp, University Duisburg-Essen, Essen, Germany
V. Vladimir Shvartsman, University Duisburg-Essen, Essen, Germany
Doru C. Lupascu, University Duisburg-Essen, Essen, Germany

High performance and small size of electronic devices are highly required qualities nowadays. However, large heat dissipation is one drawback using miniaturized high power electronic components. Hence, demand in environmentally friendly and miniaturized refrigeration systems is increased. Over the past decade the electrocaloric effect (ECE) has attracted much attention as a promising alternative cooling technology. ECE is a change of entropy or temperature of a dielectric material under an applied electric field at isothermal or adiabatic conditions, respectively. A Solid-state refrigeration system based on the ECE should combine high efficiency and low cost and should be environmentally friendly and easy scalable. Therefore, search for environmentally friendly materials with large ECE is necessary.

In this presentation, we report on the development of two experimental setups to measure the ECE directly: A custom built quasi-adiabatic calorimeter and a modified commercial differential scanning calorimeter [1]. The setups allow measurements in the temperature range 230-420 K at applied electric fields up to 40 kV/cm. We performed the ECE measurements in several lead-free ferroelectric ceramics:
• (1-x)Ba(Zr_0.2Ti_0.8)O_3-x(Ba_0.7Ca_0.3)TiO₃[2],
• 0.55Ba(Zr_0.2Ti_0.8)O_3-0.45(Ba_0.7Ca_0.3)TiO₃ with Fe and Nb doping,
• (1-x)Ba(Sn_0.15Ti_0.85)O_3-x(Ba_0.7Ca_0.3)TiO₃.

Temperature, electric field and composition dependences of the electrocaloric effect have been studied. Furthermore, results of the direct ECE measurements are compared with frequently used indirect estimations based on Maxwell relations to judge the compatibility of these measurement methods.

References
[1] M. Sanlialp, V.V. Shvartsman, C.Molin, S. Gebhardt, D. C. Lupascu. Direct Electrocaloric Measurements Using a Differential Scanning Calorimeter. IEEE proceedings, 2015.
[2] M. Sanlialp, V.V. Shvartsman, M. Acosta, B. Dkhil, D. C. Lupascu. Strong electrocaloric effect in lead-free 0.65Ba(Zr_0.2Ti_0.8)O_3-0.35(Ba_0.7Ca_0.3)TiO₃ ceramics obtained by direct measurements. APL, 2015.

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