High-entropy materials for thermoelectric applications: towards performance and reliability.

High-entropy materials (HEMs), including alloys, ceramics and other entropy-stabilized compounds, have attracted considerable attention in different application fields. This is due to their intrinsically unique concept and properties, such as innovative chemical composition, structural characteristics, and correspondingly improved functional properties. By establishing an environment with different chemical compositions, HEMs as novel materials possessing superior attributes present unparalleled prospects when compared with their conventional counterparts. Notably, great attention has been paid to investigating HEMs such as thermoelectrics (TE), especially for application in energy-related fields. In this review, we started with the basic definitions of TE fundamentals, the existing thermoelectric materials (TEMs), and the strategies adopted for their improvement. Moreover, we introduced HEMs, summarized the core effects of high-entropy (HE), and emphasized how HE will open up new avenues for designing high-entropy thermoelectric materials (HETEMs) with promising performance and high reliability. Through selecting and analyzing recent scientific publications, this review outlines recent scientific breakthroughs and the associated challenges in the field of HEMs for TE applications. Finally, we classified the different types of HETEMs based on their structure and properties and discussed recent advances in the literature.

Thickness Effect on the Solid-State Reaction of a Ni/GaAs System.

Ni thin films with different thicknesses were grown on a GaAs substrate using the magnetron sputtering technique followed by in situ X-ray diffraction (XRD) annealing in order to study the solid-state reaction between Ni and GaAs substrate. The thickness dependence on the formation of the intermetallic phases was investigated using in situ and ex situ XRD, pole figures, and atom probe tomography (APT). The results indicate that the 20 nm-thick Ni film exhibits an epitaxial relation with the GaAs substrate, which is (001) Ni//(001) GaAs and [111] Ni//[110] GaAs after deposition. Increasing the film's thickness results in a change of the Ni film's texture. This difference has an impact on the formation temperature of Ni3GaAs. This temperature decreases simultaneously with the thickness increase. This is due to the coherent/incoherent nature of the initial Ni/GaAs interface. The Ni3GaAs phase decomposes into the binary and ternary compounds xNiAs and Ni3-xGaAs1-x at about 400 °C. Similarly to Ni3GaAs, the decomposition temperature of the second phase also depends on the initial thickness of the Ni layer.