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Abstract: Titanium borates show promising hydrogen storage characteristics. Structural relaxation around individual hydrogen atoms and the binding energies are studied by means of the density functional theory methods for a number of hydrogenated TiB2 , TiB and Ti2B structures. Starting with the possible symmetric hydrogen sites a random structure searching has been performed, in addition to locate all energetically stable adsorption sites. It is shown that for the three bulk compounds considered, the lowest binding energies are obtained for TiB2 (in the 0.3–1.8 eV range), the largest for Ti2B (in the 3.9–4.7 eV range), while for TiB they are intermediate (in the 2.8–3.5 eV range). Calculations performed on hydrogenated Ti2B result in two energetically stable sites for two different starting environments, suggesting a possible soft mode solution. [Copyright &y& Elsevier]

Abstract: Charge density wave (CDW) ordering in the prototypical low-dimensional compound NbSe3 is reconsidered. It is shown that the model with two incommensurate modulations, and , localized on type-III and type-I bi-capped trigonal prismatic columns, does not explain details, revealed by various microscopic methods. An alternative explanation, based on the existence of modulated layered nano-domains below both CDW onset temperatures, is suggested. It accounts for the presence of the modulation in the STM images recorded above the CDW transition and for the absence of satellites in the corresponding diffraction patterns. The long periodic modulation, detected by LT STM, is attributed to a beating between the two CDWs, centered on adjacent columns of the same type. Such pairs of alternatively modulated columns represent the basic modulation units, ordered into nano-domains. [ABSTRACT FROM AUTHOR]

We report on high temperature (T) studies of conductivity, σ, of the monoclinic phase of NbS 3 (NbS 3 -II). The compound is shown to be stable up to T ∼550 K. Threshold non-linear conductivity and Shapiro steps on the I – V curves can be seen up to T P0 ≈ 450 – 475 K clearly demonstrating sliding of a charge-density wave (CDW). The feature in σ(T) shows that T P0 is the temperature of the formation of this CDW. The charges condensed in this CDW show relatively high density and, at the same time, extremely low mobility. Their mobility appears low in the single-particle states as well, giving a plausible clue to the surprising dielectric-like temperature variation of σ above T P0. Image 1 • The highest temperature of a charge-density wave (CDW) transition, T P0 =450 – 475 K. • Coherent sliding of this CDW and its synchronization under rf field. • Formation of the CDW from non-metallic electronic state. • High density and extremely low mobility of charges in this CDW. • The Shapiro steps provide a way to estimate carrier mobilities above a CDW transition. • Correlation of the mobilities of charges in the condensed and single-particle states for all the three CDWs in NbS 3. [ABSTRACT FROM AUTHOR]

We review the features of the charge density wave (CDW) conductor NbS3 (phase II) and include several additional results from transport, compositional, and structural studies. Particularly, we highlight three central results: (1) In addition to the previously reported CDW transitions at TP1=360K and TP2=150K, a third CDW transition occurs at a much higher temperature TP0620-650K; evidence for the nonlinear conductivity of this CDW is presented. (2) We show that the CDW associated with the TP2 transition arises from S vacancies acting as donors. Such a CDW transition has not been observed before. (3) We demonstrate the exceptional coherence of the TP1 CDW at room temperature. The effects of uniaxial strain on the CDW transition temperature and transport are reported. [ABSTRACT FROM AUTHOR]