Mg₃Bi_2-xSb_x (0 ≤ x ≤ 2) have gained significant attention due to their potential in thermoelectric (TE) applications. However, there has been much debating regarding their structural properties and phase diagram as a function of pressure, which is crucial for understanding of their TE properties. Here, we investigate a unified phase diagram of Mg₃(Bi,Sb)₂ materials up to 40 GPa at room temperature using high-pressure X-ray diffraction. Two high-pressure phases with the structural transition succession of P3m1→ C2/m → P2₁/n are observed, which is valid for all Mg₃Bi_2-xSb_x (0 ≤ x ≤ 2) compounds. We further explore the low-pressure phase P3m1 and report that alloying does not change the quasi-isotropic compression of the unit lattice parameters nor has effect on the anisotropic bond compressibility, as recently reported for the end-members. Our study presents a comprehensive picture of Mg₃Bi_2-xSb_x as a function of pressure and chemical composition providing a solid foundation for the future experimental and theoretical studies searching for the most efficient TE compound in Mg₃(Bi,Sb)₂.

Flexible solid-state cooling devices with high efficiency are attracted to ferroelectric polymers with excellent negative electrocaloric (EC) effects. It is challenging to obtain a large negative EC effect in ferroelectric polymers due to the lack of tunable techniques. A giant negative EC response was obtained in the poly(vinylidene fluoride-trifluoroethylene) copolymers (P(VDF-TrFE), 70/30, in mole ratio) irradiated with high-energy X-ray. The irradiated P(VDF-TrFE) films showed an adiabatic temperature change of −13.5 K at 40 MV/m under a dose of 5 Mrad (1 Mrad=10⁴ J/kg) obtained by the indirect method. This significant negative EC effect is attributed to the enhancement of crystalline due to the entry of polymer molecules into the amorphous to crystalline structure and the reduction of heat capacity due to the increase of crosslinking. In addition, X-ray irradiation improves the dielectric coefficient from 15 to 22. This research indicates that irradiation can modify the negative EC properties of ferroelectric polymers for solid-state cooling.

Room-temperature thermoelectric materials provide promising solutions for energy harvesting from the environment, and deliver a maintenance-free power supply for the internet-of-things (IoTs). The currently available Bi₂Te₃ family discovered in the 1950s, still dominates industrial applications, however, it has serious disadvantages of brittleness and the resource shortage of tellurium (1 × 10⁻³ ppm in the earth's crust). The novel Mg₃Sb₂ family has received increasing attention as a promising alternative for room-temperature thermoelectric materials. In this review, the development timeline and fabrication strategies of the Mg₃Sb₂ family are depicted. Moreover, an insightful comparison between the crystallinity and band structures of Mg₃Sb₂ and Bi₂Te₃ is drawn. An outlook is presented to discuss challenges and new paradigms in designing room-temperature thermoelectric materials.

The past years has observed a significantly boost of the thermoelectric materials in the scale of thermoelectric figure-of-merit, i.e. ZT, because of its promising application to harvest the widely distributed waste heat. However, the simplified thermoelectric materials' performance scale also shifted the focus of thermoelectric energy conversion technique from devices-related efforts to materials-level works. As a result, the thermoelectric devices-related works didn't get enough attention. The device-level challenges behind were kept unknown until recent years. However, besides the thermoelectric materials properties, the practical energy conversion efficiency and service life of thermoelectric device is highly determined by assembling process and the contact interface. In this perspective, we are trying to shine some light on the device-level challenge, and give a special focus on the thermoelectric interface materials (TEiM) between the thermoelectric elements and electrode, which is also known as the metallization layer or solder barrier layer. We will go through the technique concerns that determine the scope of the TEiM, including bonding strength, interfacial resistance and stability. Some general working principles are summarized before the discussion of some typical examples of searching proper TEiM for a given thermoelectric conversion material.