The solution synthesis route as a scalable bottom-up synthetic method possesses significant advantages for synthesizing nanostructured bulk thermoelectric (TE) materials with improved performance. Tuning the composition of the materials directly in the solution, without needing any further processing, is important for adjusting the dominant carrier type. Here, we report a very rapid (2 min) and high yield (>8 g/batch) synthetic method using microwave-assisted heating, for the controlled growth of Bi_2–xSb_xTe₃ (x: 0–2) nanoplatelets. Resultant materials exhibit a high crystallinity and phase purity, as characterized by XRD, and platelet morphology, as revealed by SEM. Surface chemistry of as-made materials showed a mixture of metallic and oxide phases, as evidenced by XPS. Zeta-potential analysis exhibited a systematic change of isoelectric point as a function of the material composition. As-made materials were directly sintered into pellets by using spark plasma sintering process. TE performance of Bi_2−xSb_xTe₃ pellets were studied, where the highest ZT values of 1.04 (at 440 K) for Bi₂Te₃ and 1.37 (at 523 K) for Sb₂Te₃ were obtained, as n- and p-type TE materials. The presented microwave-assisted synthesis method is energy effective, a truly scalable and reproducible method, paving the way for large scale production and implementation of towards large-area TE applications.

Scalable synthetic strategies for high-quality and reproducible thermoelectric (TE) materials is an essential step for advancing the TE technology. We present here very rapid and effective methods for the synthesis of nanostructured bismuth telluride materials with promising TE performance. The methodology is based on an effective volume heating using microwaves, leading to highly crystalline nanostructured powders, in a reaction duration of two minutes. As the solvents, we demonstrate that water with a high dielectric constant is as good a solvent as ethylene glycol (EG) for the synthetic process, providing a greener reaction media. Crystal structure, crystallinity, morphology, microstructure and surface chemistry of these materials were evaluated using XRD, SEM/TEM, XPS and zeta potential characterization techniques. Nanostructured particles with hexagonal platelet morphology were observed in both systems. Surfaces show various degrees of oxidation, and signatures of the precursors used. Thermoelectric transport properties were evaluated using electrical conductivity, Seebeck coefficient and thermal conductivity measurements to estimate the TE figure-of-merit, ZT. Low thermal conductivity values were obtained, mainly due to the increased density of boundaries via materials nanostructuring. The estimated ZT values of 0.8–0.9 was reached in the 300–375 K temperature range for the hydrothermally synthesized sample, while 0.9–1 was reached in the 425–525 K temperature range for the polyol (EG) sample. Considering the energy and time efficiency of the synthetic processes developed in this work, these are rather promising ZT values paving the way for a wider impact of these strategic materials with a minimum environmental impact.

Serial femtosecond crystallography (SFX) has become one of the standard techniques at X-ray free-electron lasers (XFELs) to obtain high-resolution structural information from microcrystals of proteins. Nevertheless, reliable sample delivery is still often limiting data collection, as microcrystals can clog both field-and flow-focusing nozzles despite in-line filters. In this study, we developed acoustic 2D focusing of protein microcrystals in capillaries that enables real-time online character-ization of crystal size and shape in the sample delivery line after the in-line filter. We used a piezoelectric actuator to create a standing wave perpendicular to the crystal flow, which focused lysozyme microcrystals into a single line inside a silica capillary so that they can be imaged using a high-speed camera. We characterized the acoustic contrast factor, focus size, and the coaxial flow lines and developed a splitting union that enables up-concentration to at least a factor of five. The focus size, flow rates, and geometry may enable an upper limit of up-concentration as high as 200 fold. The novel feedback and concentration control could be implemented for serial crystallography at synchrotrons with minor modifications. It will also aid the development of improved sample delivery systems that will increase SFX data collection rates at XFELs, with potential applications to many proteins that can only be purified and crystallized in small amounts.