Caloric Effects in Ferroic Materials: New Concepts for Cooling

Abstract

Refrigeration is one of the primary uses for electrical energy and an important contributor to worldwide CO2 emissions. Both of these issues can be mitigated if caloric effects in solid materials are fully utilized. In particular, materials with ferroic phase transitions, which give rise to magneto‐, electro‐, and elasto‐caloric effects, are promising candidates. Because these refrigerants are in the solid state, the corresponding cooling technology also eliminates the need for halo‐carbon refrigerants with high global warming potential. This Special Issue gives an overview on recent breakthroughs in the research on magnetocaloric, elastocaloric, and electrocaloric materials and their implementation in more efficient cooling devices, as obtained within the German Priority Program Ferroic Cooling (SPP 1599). As a brief introduction to the in‐depth Reviews and Full Papers included in the Special Issue, a ferroic cooling cycle is sketched and the influences of magnetic, electric, and stress fields on ferroic materials are summarized in this Editorial.

An abnormal meta-stable nanoscale eutectic reaction revealed by in-situ observations

“…In many cases, metastable phases, which form more complex crystal structure, have larger unit cells or are even aperiodic, compared to their equilibrium phases [3][4][5][6][7][8]. When cooling rate is sufficient to form a glass, subsequent annealing and devitrification can produce finely controlled nanostructures for magnetic alloys [9,10], caloric materials [11][12][13][14], nanowires [15], and even structural alloys [16,17]. However, understanding and predicting the thermodynamic and kinetic pathways for phase selection far from equilibrium is a daunting challenge, since most thermodynamic models assume phase changes occur near thermodynamic equilibrium [18].…”

Nucleation and growth of hierarchical martensite in epitaxial shape memory films

“…One example is provided by Ni-Mn-Ga magnetic shape memory alloys [1] where the presence of either type I or type II twin boundaries within the martensitic microstructure results in twinning stresses [2] and mobilities differing [3] by an order of magnitude. Another key functional property depending on the microstructure is the transformation hysteresis loss, which must be as low as possible for magnetocaloric and elastocaloric refrigeration [4].…”

Understanding the Thermodynamic Properties of the Elastocaloric Effect Through Experimentation and Modelling

“…It should be noted that the eCE is in many ways analogue to other so-called (ferro-)caloric effects such as magnetocaloric, electrocaloric and barocaloric effect [35][36][37][38][39]. Among them, to this point the most widely studied is the magnetocaloric effect, so research and experimental methods on other ferro-caloric effects can benefit from much of the existing magnetocaloric literature.…”