Walther Nernst

Résumé

Walther Hermann Nernst ( à Briesen, en province de Prusse - à Zibelle, Reich allemand) est un physicien et chimiste allemand, lauréat du prix Nobel de chimie de 1920. Il a mené de nombreuses recherches dans les domaines de l'électrochimie, de la thermodynamique, de la chimie du solide et de la photochimie. Ses découvertes incluent également l'équation qui porte son nom. Biographie W. H. Nernst est né à Briesen, en province de Prusse en 1864. Il a étudié la physique et les mathématiques aux universités de Zurich, Berlin et Graz. Il est ensuite professeur de chimie physique à l'université de Leipzig. Nernst inventa, en 1898, une lampe électrique avec un filament métallique. Cette lampe, qui a succédé aux lampes avec un filament en carbone, est un précurseur des lampes à incandescence actuelles. Vers 1906, Nernst établit le théorème précurseur de ce qui est aujourd'hui connu sous le nom de troisième principe de la thermodynamique. En 1911, ave

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Anomalous Nernst effect in Co2MnGa thin films with perpendicular magnetic anisotropy

Jean-Philippe Ansermet, Simon Granville, Junfeng Hu, Song Liu, Sa Tu, Haiming Yu, Yan Zhang

The thermoelectric and transport properties of MgO/Co2MnGa/Pd stacks with perpendicular magnetic anisotropy were measured. For a nominal 3.3 nm Co2MnGa thickness, the anomalous Nernst coefficient and the Nernst angle at room temperature were found to be 0.3 +/- 0.05 mu V/K and 5 +/- 1%, respectively. The Nernst and Hall angle temperature dependences show similar trends. Increasing the Co2MnGa thickness to 3.6 nm enhances the anomalous Nernst angle to 6.5% at room temperature. At remanence, the anomalous Nernst coefficient at room temperature is half the saturation value.

ELSEVIER2020

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Effects of Driving Forces for Recombination and Regeneration on the Photovoltaic Performance of Dye-Sensitized Solar Cells using Cobalt Polypyridine Redox Couples

Ulf Anders Hagfeldt, Gang Wang

Dye-sensitized solar cells with open-circuit potentials above 1 V were obtained by employing the triphenylamine-based org. dye D35 in combination with cobalt phenanthroline redox couples. A series of cobalt bipyridine and cobalt phenanthroline complexes with different redox potentials were investigated to examine the dependence of the driving force for recombination and dye regeneration on the photovoltaic performance. The photovoltage of the devices was found to increase and the photocurrent to decrease with increasing redox potential of the complexes. The halftime for regeneration of the oxidized dye by cobalt tris(bipyridine) was about 20 μs, similar to that found for the iodide/triiodide redox couple, whereas regeneration kinetics became slower for cobalt complexes with less driving force for regeneration. A driving force for dye regeneration of 390 mV for cobalt(II/III) tris(5-chloro-1,10-phenanthroline) was found sufficient to regenerate more than 80% of the D35 dye mols., resulting in a conversion of incident photons-to-elec. current of above 80%. The photocurrent of the D35-sensitized solar cells using cobalt phenanthroline complexes decreased, however, with increasing Nernst potential of the redox couples, due to the increased recombination and the decreased regeneration rate consts.

2011

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, ,

Spin caloritronics refers to research efforts in spintronics when a heat current plays a role. In this review, we start out by reviewing the predictions that can be drawn from the thermodynamics of irreversible processes. This serves as a conceptual framework in which to analyze the interplay of charge, spin and heat transport. This formalism predicts tensorial relations between vectorial quantities such as currents and gradients of chemical potentials or of temperature. Transverse effects such as the Nernst or Hall effects are predicted on the basis that these tensors can include an anti-symmetric contribution, which can be written with a vectorial cross-product. The local symmetry of the system may determine the direction of the vector defining such transverse effects, such as the surface of an isotropic medium. By including magnetization as state field in the thermodynamic description, spin currents appear naturally from the continuity equation for the magnetization, and dissipative spin torques are derived, which are charge-driven or heat-driven. Thermodynamics does not give the strength of these effects, but may provide relationships between them. Based on this framework, the review proceeds by showing how these effects have been observed in various systems. Spintronics has become a vast field of research, and the experiments highlighted in this review pertain only to heat effects on transport and magnetization dynamics, such as magneto-thermoelectric power, or the spin-dependence of the Seebeck effect, the spin-dependence of the Peltier effect, the spin Seebeck effect, the magnetic Seebeck effect, or the Nernst effect. The review concludes by pointing out predicted effects that are yet to be verified experimentally, and in what novel materials the standard thermal spin effects could be investigated.

Elsevier2016

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