Magnetocaloric effect: From materials research to refrigeration devices

The magnetic refrigeration technique based on the magnetocaloric effect (MCE) has attracted increasing interest because of its high efficiency and environment friendliness. in this article, our recent progress in exploring effective MCE materials is reviewed with emphasis on the MCE in the LaFe13-xSix-based alloys discovered by us. These alloys show large entropy changes over a wide temperature range near room temperature. The effects of magnetic rare-earth doping, interstitial atoms and high pressure on the MCE have been systematically studied. Special issues, such as appropriate approaches to determining the MCE associated with the first-order magnetic transition, the depression of magnetic and thermal hysteresis, and the key factors determining the magnetic exchange in alloys of this kind, are discussed. The applicability of giant MCE materials to magnetic refrigeration near ambient temperature is evaluated. A brief review of other materials with significant MCE is also presented.

Recent Progress in Exploring Magnetocaloric Materials

Negative thermal expansion (NTE) is an intriguing physical property of solids, which is a consequence of a complex interplay among the lattice, phonons, and electrons. Interestingly, a large number of NTE materials have been found in various types of functional materials. In the last two decades good progress has been achieved to discover new phenomena and mechanisms of NTE. In the present review article, NTE is reviewed in functional materials of ferroelectrics, magnetics, multiferroics, superconductors, temperature-induced electron configuration change and so on. Zero thermal expansion (ZTE) of functional materials is emphasized due to the importance for practical applications. The NTE functional materials present a general physical picture to reveal a strong coupling role between physical properties and NTE. There is a general nature of NTE for both ferroelectrics and magnetics, in which NTE is determined by either ferroelectric order or magnetic one. In NTE functional materials, a multi-way to control thermal expansion can be established through the coupling roles of ferroelectricity-NTE, magnetism-NTE, change of electron configuration-NTE, open-framework-NTE, and so on. Chemical modification has been proved to be an effective method to control thermal expansion. Finally, challenges and questions are discussed for the development of NTE materials. There remains a challenge to discover a “perfect” NTE material for each specific application for chemists. The future studies on NTE functional materials will definitely promote the development of NTE materials.

Negative thermal expansion in functional materials: controllable thermal expansion by chemical modifications

Magnetocaloric materials with a Curie temperature near room temperature have attracted significant interest for some time due to their possible application for high-efficiency refrigeration devices. This review focuses on a number of key issues of relevance for the characterization, performance and implementation of such materials in actual devices. The phenomenology and fundamental thermodynamics of magnetocaloric materials is discussed, as well as the hysteresis behavior often found in first-order materials. A number of theoretical and experimental approaches and their implications are reviewed. The question of how to evaluate the suitability of a given material for use in a magnetocaloric device is covered in some detail, including a critical assessment of a number of common performance metrics. Of particular interest is which non-magnetocaloric properties need to be considered in this connection. An overview of several important materials classes is given before considering the performance of materials in actual devices. Finally, an outlook on further developments is presented.

Materials Challenges for High Performance Magnetocaloric Refrigeration Devices

The primary goal of this review is to present a clear chemical perspective of borates in order to stimulate and facilitate the discovery of new borate-based optical materials. These materials, whic...

Borates: A Rich Source for Optical Materials.

Phase diagram, ferromagnetic martensitic transformation and magnetoresponsive properties of Fe-doped MnCoGe alloys

Based on the Bean–Rodbell model, which assumes a linear variation of exchange coupling with atom spacing, the magnetovolume effects in LaFe13−xSix (x = 1.2–2.0) have been systematically studied. A relation between phase volume and magnetization is first obtained by comparing the structural and magnetic data collected at various temperatures. The maximum spontaneous magnetostriction thus derived is dependent on the content of Si, linearly decreasing from ~2.15% for x = 1.2 to ~1.12% for x = 2. Based on these results and limited experimental data, the parameters involved in the Bean–Rodbell model are determined for the LaFe13−xSix compounds. Further analysis indicates that the Bean–Rodbell model equipped with these parameters gives a satisfactory description of the magnetovolume effects produced by interstitial hydrogen for the LaFe11.44Si1.56 hydride. To explain the pressure effects, in contrast, changes of the parameters under pressure, which are a result of the enhancement of the first-order character of the phase transition, have to be taken into account. These results indicate that either the increase or the decrease of the Curie temperature is simply a consequence of the variation of the phase volume due to the introduction of interstitial atoms or the application of a high pressure, and can be described well by the Bean–Rodbell model.

http://iopscience.iop.org/article/10.1088/0953-8984/18/44/002/pdf

Magnetovolume effect in intermetallics LaFe13-xSix

Synthesis and luminescent properties of Eu 3+ , Eu 3+ /Bi 3+ and Gd 3+ codoped YAG:Ce 3+ phosphors and their potential applications in warm white light-emitting diodes

Huadi Zhang

Papers

Phase diagram, ferromagnetic martensitic transformation and magnetoresponsive properties of Fe-doped MnCoGe alloys

Magnetovolume effect in intermetallics LaFe13-xSix

Synthesis and luminescent properties of Eu 3+ , Eu 3+ /Bi 3+ and Gd 3+ codoped YAG:Ce 3+ phosphors and their potential applications in warm white light-emitting diodes

Influence of interstitial and substitutional atoms on the crystal structure of La(FeSi)13

Dependence of emitting light for LEDs fabricated by YAG:Ce crystal wafer on wafer thickness