No abstract available

[en] We have extended the search for topological insulators to the ternary tetradymite-like compounds M₂X₂Y (M=Bi or Sb; X and Y=S, Se or Te), which are variations of the well-known binary compounds Bi₂Se₃ and Bi₂Te₃. Our first-principles computations suggest that five existing compounds are strong topological insulators with a single Dirac cone on the surface. In particular, stoichiometric Bi₂Se₂S, Sb₂Te₂Se and Sb₂Te₂S are predicted to have an isolated Dirac cone on their naturally cleaved surface. This finding paves the way for the realization of the topological transport regime.

[en] Thermoelectricity offers a green, clean and safe energy conversion technology as a remedy for both environmental issues like green house effect, global warming and environmental pollution an depletion of natural resources. Here we synthesize nanostructured Bi₂Te₃ by vacuum heating and ball milling and the nanostructured material is compacted by using hot pressing method

[en] Bismuth tellurite is a photorefractive material for holographic data storage offering unique fixing capabilities. Important material and electro-optic properties obtained by four-wave-mixing and data storage experiments are reviewed and recent results concerning the applicability of bismuth tellurite for holographic data storage, including dynamic range, multiplexing capabilities and bit-error evaluations, are presented. Furthermore, it is demonstrated how the latest progress in growing Bi₂TeO₅ made this crystal a candidate for durable holographic recording media.

No abstract available

[en] Highlights: • Stoichiometric Bi_0.5Sb_1.5Te₃ films are fabricated by in-situ crystallization. • The (000l) orientations and high crystallinity of these films have been realized. • Three parameters of electrical properties (μ, σ, α) are simultaneously increased. • The relationship between the electric properties and orientations are calculated. • A layer-by-layer in-situ growth model is proposed for (000l)-oriented films. The preparation of high-performance Bi₂Te₃-based films is vitally important for the miniaturization of Bi₂Te₃ thermoelectric (TE) device. Herein, a series of stoichiometric Bi_0.5Sb_1.5Te₃ films with different preferential orientations have been fabricated through in-situ crystallization during the co-sputtering process. We discover that the preferential orientation was transformed from (01$\bar{\text{1}}$5) to (10$\bar{\text{1}}$10) to (000l) orientation with increasing the substrate temperature. The (000l)-oriented films exhibit the best electrical transport properties, which the maximum electrical conductivity of 8.0×10⁴ S·m^-1 and power factor of 3.8 mW K^-2·m^-1 are much more than those of the bulk material. The excellent properties are attributed to the high-crystallinity, well-controlled preferential orientation, and minimized compositional deviation. A layer-by-layer in-situ growth model is proposed to understand the formation mechanism of the (000l)-oriented films. Our work demonstrates that the electrical transport performance of Bi₂Te₃-based films can be remarkably improved through finely controlling the crystallinity and preferential orientation under the condition of stoichiometric composition.

No abstract available

[en] The bandstructures of [110] and [001] Bi_2Te_3 nanowires are solved with the atomistic 20 band tight binding functionality of NEMO5. The theoretical results reveal: The popular assumption that all topological insulator (TI) wire surfaces are equivalent is inappropriate. The Fermi velocity of chemically distinct wire surfaces differs significantly which creates an effective in-surface confinement potential. As a result, topological insulator surface states prefer specific surfaces. Therefore, experiments have to be designed carefully not to probe surfaces unfavorable to the surface states (low density of states) and thereby be insensitive to the TI-effects

[en] By methods of X-ray phase, differential thermal, microstructural analyses the interaction in ZnTe-BiTe and ZnTe-Bi₂Te₂ is studied. It is shown that the ZnTe-Bi₂Te₃ section is quasibinary and the ZnTe-BiTe section is non-quasibinary in the Zn-Bi-Te ternary system. The phase diagram of the ZnTe-Bi₂Te₃ system is peritectic, solid solution based on bismuth telluride at 500 deg contains 5 mol% of zinc telluride. According to X-ray phase analysis in the whole region of the ZnTe-BiTe system compositions only phases on ZnTe and BiTe base (annealing at 500 deg) have been found

[en] The dimensionless thermoelectric figure-of-merit, ZT, of Bi₂Te₃ based alloys was investigated under a large temperature difference using a recently reported 'open/short circuit' measurement technique. It is shown that the measured ZT decreases with an increase in temperature difference. Theoretical analysis indicates that this dependence can be explained by taking into account the Thomson effect. An equation is obtained for a modified thermoelectric figure-of-merit which is valid for measurement over large temperature differences