Thermoelectric harvesting of waste heat offers great opportunities for energy production. Here, we demonstrated that a minor Cu addition in the n-type Mg 3 Sb 1.5 Bi 0.5 realized the remarkable enhancement of low-temperature thermoelectric performance. Coupled with p-type a-MgAgSb, we fabricated a high-performance thermoelectric module, which showed a record-high conversion efficiency of 7.3% at the hot-side temperature of 593 K. Our module rivals the longtime champion Bi 2 Te 3 in this applicably important temperature range, providing great promise for harvesting abundant low-grade waste heat.

We synthesized freestanding bulk three-dimensional nanoporous Si using dealloying in a metallic melt, a top-down process. Using this nanoporous Si, we fabricated negative electrodes with high lithium capacity, nearing their theoretical limits, and greatly extended cycle lifetimes, considerably improving the battery performance compared with those using electrodes made from silicon nanoparticles. By operating the electrodes below the accommodation volume limit of their pores, we prolonged their cycle lifetime.

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High-entropy alloys (HEAs) with an atomic arrangement of a hexagonal closepacked (hcp) structure were found in YGdTbDyLu and GdTbDyTmLu alloys as a nearly single hcp phase. The equi-atomic alloy design for HEAs assisted by binary phase diagrams started with selecting constituent elements with the hcp structure at room temperature by permitting allotropic transformation at a high temperature. The binary phase diagrams comprising the elements thus selected were carefully examined for the characteristics of miscibility in both liquid and solid phases as well as in both solids due to allotropic transformation. The miscibility in interest was considerably narrow enough to prevent segregation from taking place during casting around the equi-atomic composition. The alloy design eventually gave candidates of quinary equi-atomic alloys comprising heavy lanthanides principally. The XRD analysis revealed that YGdTbDyLu and GdTbDyTmLu alloys thus designed are formed into the hcp structure in a nearly single phase. It was found that these YGdTbDyLu and GdTbDyTmLu HEAs with an hcp structure have delta parameter (d) values of 1.4 and 1.6, respectively, and mixing enthalpy (DH mix ) = 0 kJ/mol for both alloys. These alloys were consistently plotted in zone S for disordered HEAs in a d-DH mix diagram reported by Zhang et al. (Adv Eng Mater 10:534, 2008). The value of valence electron concentration of the alloys was evaluated to be 3 as the first report for HEAs with an hcp structure. The finding of HEAs with the hcp structure is significant in that HEAs have been extended to covering all three simple metallic crystalline structures ultimately followed by the body-and facecentered cubic (bcc and fcc) phases and to all four simple solid solutions that contain the glassy phase from high-entropy bulk metallic glasses.

Most nanomaterials, such as transition metal carbides, phosphides, nitrides, chalcogenides, etc., have been extensively studied for their various properties in recent years. The similarly attractive transition metal borides, on the contrary, have seen little interest from the materials science community, mainly because nanomaterials are notoriously difficult to synthesize. Herein, a simple, general synthetic method toward crystalline transition metal boride nanomaterials is proposed. This new method takes advantage of the redox chemistry of Sn/SnCl , the volatility and recrystallization of SnCl at the synthesis conditions, as well as the immiscibility of tin with boron, to produce crystalline phases of 3d, 4d, and 5d transition metal nanoborides with different morphologies (nanorods, nanosheets, nanoprisms, nanoplates, nanoparticles, etc.). Importantly, this method allows flexibility in the choice of the transition metal, as well as the ability to target several compositions within the same binary phase diagram (e.g., Mo B, α-MoB, MoB , Mo B ). The simplicity and wide applicability of the method should enable the fulfillment of the great potential of this understudied class of materials, which show a variety of excellent chemical, electrochemical, and physical properties at the microscale.