Contributed by IRG 2 Members: Yeongwoo Son and Susan E. Trolier-McKinstry
Yeongwoo Son and Susan Trolier-McKinstry, “Electrocaloric Effect of Perovskite High Entropy Films,” Adv. Electron. Mat. 8 2200352 (2022). DOI: 10.1002/aelm.202200352
Pb(Hf0.2Zr0.2Ti0.2Nb0.2X0.2)O3, a high-entropy perovskite, undergoes an entropy-driven phase transformation when X=Mn while X=Al always contains minor second phases in bulk ceramics. Thin films with X=Al show a narrow ferroelectric hysteresis loop and relaxor-like characteristics, i.e. a high dielectric permittivity of ~2000 and low dielectric loss. These are the characteristics needed for device applications.
Indirect measurements (based on Maxwell relations) yield a electrocaloric temperature change of 8.4 K at 180°C under an applied electric field of 1186 kV cm−1. The temperature changes in this initial example of a high-entropy electrocaloric oxide are already comparable to those of other oxide-based materials. The huge design space available for optimization of high-entropy formulations now offers opportunities to exceed known electrocalorics in terms of both size of response and operating temperature range.
What Has Been Achieved: The IRG team has prepared bulk and thin film embodiments of new high entropy relaxor ferroelectric phases. The formulations are chosen to include different types of disorder: size, valence, electronegativity, etc. The high entropy state extends solubility so that many categories of disorder can be sampled.
Importance of the Achievement: Confirmation of the high entropy concept’s connection to the electrocaloric effect will allow the MRSEC to design new perovskite high entropy materials that maximize the polarization entropy change upon field cycling, and thus the associated temperatures changes. The opportunity is to make electrocaloric refrigeration more efficient, which is hugely important in terms of sustainability concerns. Refrigeration is just behind transportation in terms of global energy consumption.
Unique Feature(s) of the MRSEC/PREM that Enabled this Achievement:. Collaborative feature of MRSEC facilitates very active interactions to result in this work. This is the first materials-based publication from which many property, characterization, and computation reports will emerge.