Berlin 2024 – wissenschaftliches Programm
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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur
KFM 33: Focus Session: (Multi-)Ferroic States V
KFM 33.5: Vortrag
Freitag, 22. März 2024, 11:05–11:25, EMH 225
Field dependence of the electrocaloric effect in ferroelectrics with first order and diffuse phase transitions — •Jan Fischer, Daniel Haegele, and Joerg Rudolph — Ruhr University Bochum
The electrocaloric effect (ECE) in ferroelectrics is currently in the focus of interest for energy efficient cooling technologies. The field dependence Δ Tad(E) of the adiabatic caloric temperature change as a key parameter of caloric materials is highly relevant both for the fundamental understanding of the ECE and for the design of caloric coolers. Traditionally, Δ T(E) has been measured only for discrete values of the electric field and the low-field range is often left unexplored.
Here, we present high-resolution measurements of the electric field dependence Δ T(E) by dynamic measurements of the IR radiation emitted by the sample [1]. We find characteristic changes of Δ T(E) within a few Kelvin as a fingerprint of the first order phase transition in BaTiO3. In contrast, investigations of Ba(Zr0.12Ti0.88)O3 show only a slow and gradual change of the field dependence over a broad temperature range as a consequence of the diffuse phase transition. Simultaneous measurements of the polarization P further allow to compare the polarization dependence Δ T(P) to predictions of Landau-Devonshire theory. In addition, single-shot measurements of the dynamics Δ T(t) for few-cycle bursts of the electric field allow, e.g., to separate hysteresis heating from the pure caloric temperature change.
[1] Fischer et al., Rev. Sci. Instrum. 94, 043906 (2023)
Keywords: Electrocaloric effect (ECE); Ferroelectrics; Phase transitions; Caloric effects; Barium titanate (BTO)