Promoted crystallisation and cationic ordering in thermoelectric Cu26V2Sn6S32 colusite by eccentric vibratory ball milling.

A pristine colusite Cu26V2Sn6S32 was successfully synthesised on a 100 g scale via a mechanochemical reaction in an industrial eccentric vibratory ball mill followed by spark plasma sintering (SPS) at 873 K. The milling of elemental precursors from 1 up to 12 hours was performed and the prepared samples were investigated in detail by X-ray powder diffraction, Mössbauer spectroscopy, scanning electron microscopy, and thermoelectric property measurements. The results point to the formation of a high purity and high crystallinity non-exsoluted colusite phase after the SPS process (P4[combining macron]3n, a = 10.7614(1) Å) in the case of a 12 h milled sample. In comparison, samples milled for 1-6 h displayed small quantities of binary Cu-S phases and vanadium core-shell inclusions, leading to a V-poor/Sn-rich colusite with a higher degree of structural disorder. These samples exhibit lower electrical conductivity and Seebeck coefficient while an increase in the total thermal conductivity is observed. This phenomenon is explained by a higher reactivity and grain size reduction upon prolonged milling and by a weak evolution of the chemical composition from a partly disordered V-poor/Sn-rich colusite phase to a well-ordered stoichiometric Cu26V2Sn6S32 colusite, which leads to a decrease in carrier concentration. For all samples, the calculated PF values, around 0.7-0.8 mW m-1 K-2 at 700 K, are comparable to the values previously achieved for mechanochemically synthesised Cu26V2Sn6S32 in laboratory mills. This approach thus serves as an example of scaling-up possibility for sulphur-based TE materials and supports their future large-scale deployment.

From crystal to glass-like thermal conductivity in crystalline minerals.

The ability of some materials with a perfectly ordered crystal structure to mimic the heat conduction of amorphous solids is a remarkable physical property that finds applications in numerous areas of materials science, for example, in the search for more efficient thermoelectric materials that enable to directly convert heat into electricity. Here, we unveil the mechanism in which glass-like thermal conductivity emerges in tetrahedrites, a family of natural minerals extensively studied in geology and, more recently, in thermoelectricity. By investigating the lattice dynamics of two tetrahedrites of very close compositions (Cu12Sb2Te2S13 and Cu10Te4S13) but with opposite glasslike and crystal thermal transport by means of powder and single-crystal inelastic neutron scattering, we demonstrate that the former originates from the peculiar chemical environment of the copper atoms giving rise to a strongly anharmonic excess of vibrational states.

Valence change and magnetic order in YbMn6Ge(6-x)Sn(x).

The YbMn(6)Ge(6-x)Sn(x) compounds (0 < x < 6) have been investigated using x-ray diffraction, magnetic measurements, neutron diffraction and (170)Yb Mössbauer spectroscopy. The YbMn(6)Ge(6-x)Sn(x) system comprises three solid solutions: (i) 0 < x ≤ 1.1, (ii) 3.2 ≤ x ≤ 4.6 and (iii) 5.3 ≤ x < 6, all of which crystallize in the hexagonal (P6/mmm) HfFe(6)Ge(6)-type structure. The substitution of Sn for Ge yields changes in the type of magnetic order (antiferromagnetic, helimagnetic, ferromagnetic, conical and ferrimagnetic), in the easy magnetization direction (from easy axis to easy plane) as well as in the valence state of Yb (from trivalent to divalent). The Mn moments order at or above room temperature, while magnetic ordering of the Yb sublattice is observed at temperatures up to 110 K. While Yb is trivalent for x ≤ 1.1 and divalent for x ≥ 5.3, both magnetic and (170)Yb Mössbauer spectroscopy data suggest that there is a gradual reduction in the average ytterbium valence through the intermediate solid solution (3.2 ≤ x ≤ 4.6), and that intermediate valence Yb orders magnetically, a very unusual phenomenon. Analysis of the (170)Yb Mössbauer spectroscopy data suggests that the departure from trivalency starts as early as x = 3.2 and the loss of ytterbium moment is estimated to occur at an average valence of ∼2.5+.

Scanning electron microscopic study of microcrystals implicated in human rheumatic diseases.

Scanning electron microscopy has been used in conjunction with wavelength dispersive X-Ray spectroscopy and in correlation with X-Ray diffraction to define the populations of crystals present in rheumatic diseases. Microcrystals of monosodium urate, triclinic and monoclinic calcium pyrophosphate dihydrate, apatite, calcium hydrogen phosphate dihydrate and corticosteroids, among others, have been found in synovial fluid, in the intraarticular tissues (fibrocartilage, cartilage, and synovial membrane), and in the periarticular tissues (tendons and ectopic calcifications). Scanning electron microscopy in conjunction with wavelength dispersive X-Ray spectroscopy has made it possible to detect microcrystals, even isolated, to describe their morphologies, and to study their relations with the cells of the synovial fluid and with the collagenous and cellular structures of the synovial membrane and of the cartilage. It cannot replace X-Ray diffraction for the conclusive identification of microcrystals, but it can certainly help to improve the analysis of the various populations of crystals present in articular and periarticular rheumatic diseases.

Identification of microcrystals in synovial fluids by combined scanning electron microscopy and x-ray diffraction : application to triclinic calcium pyrophosphate dihydrate.

We report a method for studying microcrystals which combines scanning electron microscopy, electron-dispersive X-ray analysis, and X-ray diffraction. Application of all three techniques to the same crystalline bodies permits correlation of their three-dimensional morphology at high magnification with unambiguous identification by means of their crystallographic properties. The method was applied to triclinic calcium pyrophosphate dihydrate.