Through transport, compositional and structural studies, we review the features of the chargedensity wave (CDW) conductor of NbS3 (phase II). We highlight three central results: 1) In addition to the previously reported CDW transitions at TP 1 = 360 K and TP 2 = 150 K, another CDW transition occurs at a much higher temperature TP 0 = 620-650 K; evidence for the non-linear conductivity of this CDW is presented. 2) We show that CDW associated with the TP 2 -transition arises from S vacancies acting as donors. Such a CDW transition has not been observed before. 3) We show exceptional coherence of the TP 1-CDW at room-temperature. Additionally, we report on the effects of uniaxial strain on the CDW transition temperatures and transport.
A series of hydrogenated cubic C15 and hexagonal C14 ZrCr 2 Laves phases were studied by means of semiempirical extended Hu ¨ckel tight-binding, ab initio density functional theory methods and maximally localized Wannier functions, with a goal to find the most energetically favorable positions of interstitial H atoms in the host unit cells. We consider situations with one or two H atoms per primitive cell. Crystalorbital overlap population studies, performed for the C15 structure, show repulsion between two hydrogen atoms in close proximity. This is in accord with the ab initio calculations, performed for the hydrogenated C14 and C15 structures, which clearly favor two separated hydrogen atoms instead of the formation of moleculelike pairs in five-coordinated trigonal-bipyramidal environments.
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