No abstract

Cu12Sb4S13 has aroused great interest because of its earth-abundant constituents and intrinsic low thermal conductivity. However, the applications of Cu12Sb4S13 are hindered by its poor thermoelectric performance. Herein, it is shown that Gd substitution not only causes a significant increase in both electrical conductivity σ and thermopower S but also leads to dramatic drop in lattice thermal conductivity κ L. Consequently, large ZT reaches 0.94 at 749 K for Cu11.7Gd0.3Sb4S13, which is ∼41% higher than the ZT value of undoped sample. Rietveld refinements of XRD results show that accompanying inhibition of impurity phase Cu3SbS4, the number of Cu vacancies increases substantially with substituted content x (x ≤ 0.3), which leads to reduced κ L owing to intensive phonon scattering by the point defects and increased σ arising from the charged defects (V Cu ’ ). Crucially, synchrotron radiation photoelectron spectroscopy reveals substantial increment of electronic density of states at Fermi level upon Gd substitution, which is proven, by our first-principle calculations, to originate from contribution of Gd 4f orbit, resulting in enhancement of S. Our study provides us with a new path to enhance thermoelectric performance of Cu12Sb4S13.

Nanoparticle assembly paves the way for unanticipated properties and applications from the nanoscale to the macroscopic world. However, the study of such material systems is greatly inhibited due to the obscure compositions and structures of nanoparticles (especially the surface structures). The assembly of atomically precise nanoparticles is challenging, and such an assembly of nanoparticles with metal core sizes strictly larger than 1 nm has not been achieved yet. Here, we introduced an on-site synthesis-and-assembly strategy, and successfully obtained a straight-chain assembly structure consisting of Ag77Cu22(CHT)48 (CHT: cyclohexanethiolate) nanoparticles with two nanoparticles separated by one S atom, as revealed by mass spectrometry and single crystal X-ray crystallography. Although Ag77Cu22(CHT)48 bears one unpaired shell-closing electron, the magnetic moment is found to be mainly localized at the S linker with magnetic isotropy, and the sulfur radicals were experimentally verified and found to be unstable after disassembly, demonstrating assembly-induced spin transfer. Besides, spin nanoparticles are found to couple and lose their paramagnetism at sufficiently short inter-nanoparticle distance, namely, the spin coupling depends on the inter-nanoparticle distance. However, it is not found that the spin coupling leads to the nanoparticle growth.