Electron doping and phonon scattering in Ti1+xS2 thermoelectric compounds

Bulk polycrystalline samples in the series Ti1+xS2 (x = 0 to 0.05) were prepared using high temperature synthesis from the elements and spark plasma sintering. X-ray structure analysis shows that the lattice constant c expands as titanium intercalates between TiS2 slabs. For x=0, a Seebeck coefficient close to -300 μV/K is observed for the first time in TiS2 compounds. The decrease in electrical resistivity and Seebeck coefficient that occurs upon Ti intercalation (Ti off stoichiometry) supports the view that charge carrier transfer to the Ti 3d band takes place and the carrier concentration increases. At the same time, the thermal conductivity is reduced by phonon scattering due to structural disorder induced by Ti intercalation. Optimum ZT values of 0.14 and 0.48 at 300K and 700K, respectively, are obtained for x=0.025

Inter-laboratory optical measurements of film thickness during annular flow condensation in a small diameter channel

In the present study, liquid film thickness measurements are performed during vertical downflow condensation inside a 3.38 mm inner diameter channel at 40 °C saturation temperature. Condensation tests are carried out with HFE-7000 in two different test apparatuses, the first being composed of two counter-flow tube-in-tube heat exchangers separated by an adiabatic borosilicate glass tube for flow visualizations and liquid film thickness measurement, while the second consisting of a diabatic sapphire tube coupled with an infrared camera for simultaneous local heat flux and film thickness measurements at low mass flux (5–30 kg m−2 s−1). Chromatic confocal imaging and shadowgraphy are applied to the adiabatic borosilicate glass tube for evaluating the liquid film thickness with high temporal and spatial resolution, while punctual optical sensors (chromatic confocal and interferometer) are used in the diabatic sapphire test section. The liquid film thickness results obtained in the two independent laboratories are compared at the same operating conditions, showing an excellent agreement. The effect of mass flux (from 50 to 150 kg m−2 s−1) and vapor quality on the liquid film thickness and interfacial waviness of HFE-7000 is discussed by means of both statistical and spectral analyses. The liquid film thickness data of HFE-7000 are compared with those of R245fa and R134a taken during previous experimental campaigns. HFE-7000 generally displays lower film thickness values compared to R245fa and R134a due to the smaller vapor density. At low mass flux (50 kg m−2 s−1), such comparison shows the effect of the small liquid viscosity on the thinning of the liquid film in the case of R134a. The accuracy of well-known models for the prediction of the mean film thickness is assessed with comparison to the experimental data of HFE-7000

Intrinsic effects of substitution and intercalation on thermal transport in two-dimensional TiS<inf>2</inf> single crystals

International audienceThe promising thermoelectric material TiS2 can be easily chemically doped and intercalated. We present here studies of single crystals that are intercalated with excess Ti or Co, or substituted with Ta. We demonstrate the intrinsic impact of these dopants on the thermal transport in the absence of grain boundary scattering. We show that Ta doping has the greatest impact on the thermal scattering rate per ion added, leading to a five-fold reduction in the lattice thermal conductivity as compared to stoichiometric single crystals. © 2015 AIP Publishing LLC

Détermination des propriétés mécaniques de matériaux très rigides : comparaison entre nanoindentation instrumentée, Microscopie à Force Atomique en mode Peak Force Tapping et Contact Résonant

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