Academic literature on the topic 'Α-MgAgSb'

α-MgAgSb is a very promising thermoelectric material with excellent thermoelectric properties between room temperature and 300 °C, a range where few other thermoelectric materials show good performance. Previous reports rely on a two-step ball-milling process and/or time-consuming annealing. Aiming for a faster and scalable fabrication route, herein, we investigated other potential synthesis routes and their impact on the thermoelectric properties of α-MgAgSb. We started from a gas-atomized MgAg precursor and employed ball-milling only in the final mixing step. Direct comparison of high energy ball-milling and planetary ball-milling revealed that high energy ball milling already induced formation of MgAgSb, while planetary ball milling did not. This had a strong impact on the microstructure and secondary phase fraction, resulting in superior performance of the high energy ball milling route with an attractive average thermoelectric figure of merit of z T avg = 0.9. We also show that the formation of undesired secondary phases cannot be avoided by a modification of the sintering temperature after planetary ball milling, and discuss the influence of commonly observed secondary phases on the carrier mobility and on the thermoelectric properties of α-MgAgSb.

P-type nanostructured α-MgAgSb by virtue of its intrinsically low thermal conductivity and environment friendly characteristics has drawn a great deal of attention for low temperature power generation.

Thorough first-principles calculations reveal that an Ag vacancy is the dominant intrinsic point defect in α-MgAgSb. Point-defect engineering can be realized via rationally controlling the hot press temperature due to the recovery effect.

The ineffectiveness of boron doping to enhance thermoelectric performance lied in the introduced perturbation to the valence band. Due to the significant solution strengthening by boron doping, the micro-hardness values of α-MgAgSb have been largely increased.

L’objectif de cette étude est de participer au développement de nouveaux nanomatériaux thermoélectriques (TE) compatibles avec la technologie CMOS, afin de développer des composants intégrés permettant de récupérer l’énergie perdue dans les dispositifs de la microélectronique. Le but est de réaliser un film mince de α, car ce composé n’est pas toxique et ses éléments ne sont pas rares contrairement aux matériaux à base de Bi et de Te. Les propriétés TE de α à l’état massif, notamment au voisinage de la température ambiante, font de ce matériau un matériau très prometteur pour les applications TE. Ce travail de thèse porte sur l’influence de la méthode d’élaboration par pulvérisation cathodique sur les températures de transition des phases Mg-Ag-Sb en film mince, ainsi que sur la microstructure des films, en lien avec leurs propriétés TE. Nos résultats montrent que l’utilisation d’une cible alliée (Mg1/3Ag1/3Sb1/3) ne permet pas d’obtenir un film homogène de α. La formation de α est accompagnée des phases secondaires Ag3Sb et Sb qui détériorent les propriétés TE du film. Cependant, il est possible de supprimer la formation de Ag3Sb grâce à la co-pulvérisation de trois cibles pures Mg, Ag et Sb, dans des conditions d’élaboration optimisées. Ces études montrent que les proportions des phases présentes dans les films affectent fortement le coefficient de Seebeck effectif (S) des films. Cependant, le rôle des interfaces entre les phases sur le S du film est négligeable. Nos observations in situ montrent que les transitions de phases ne sont pas allotropique comme généralement admis. Ces trois phases possèdent des compositions différentes et ne sont pas stœchiométriques
The goal of the present study is to participate to the development of new thermoelectric nanomaterials (TE) compatible with the CMOS technology, allowing integrated components able to use lost thermal energy in integrated circuits to power microelectronic devices to be developed. Unlike bismuth and tellurium based materials, the compound α MgAgSb is made of nontoxic and abundant elements. The TE properties of bulk α MgAgSb, especially at room temperature, were shown to be very promising for TE applications. The goal of this PhD work is to investigate the possibility of producing α thin films using magnetron sputtering deposition technique. The influence of the elaboration method on the Mg-Ag-Sb phase transitions in thin films as well as on the film microstructure is investigated in relation with the film TE properties. The results show that the use of an alloyed target (Mg1/3Ag1/3Sb1/3) does not allow a homogeneous α film to be produced. The formation of the phase α is always accompanied with the formation of the secondary phases Ag3Sb and Sb that deteriorate the film TE properties. However, it is possible to suppress the formation of Ag3Sb by co sputtering three pure targets Mg, Ag, and Sb, using optimized sputtering conditions. This study shows that the proportion of the different phases in the films strongly affects the effective Seebeck coefficient (S) of the films. However, the contribution of the interfaces between the nanometric grains of these phases on S is negligible. Contrasting with the general assumption, our in situ observations indicate that the phase transitions are not allotropic. These three phases have different compositions and are non stoichiometric