Transport properties of Bi-rich Bi-Sb alloys

Thermoelectric properties of (BixSb1−x)2Te3 single crystal solid solutions grown by the T.H.M. method

High thermoelectric performance in (Bi0.25Sb0.75)2Te3 due to band convergence and improved by carrier concentration control

An atomic-scale graded structure was formed by the sedimentation of component atoms in an all-proportional miscible alloy under a strong gravitational field of 1 million g in maximum acceleration at high temperature. Continuous composition gradients of Sb (about 20–0 wt. %) and Bi (about 80–100 wt. %) and the resultant continuous change in the lattice constants were observed in the ultracentrifuged Bi–Sb (70:30 in mol %) alloy bulk body. Crystal growth in the direction of acceleration field was also observed. It must be noted that the substitutional solute atoms with component level rate acted in the sedimentation of this system, while interstitial solutes (Au) at an impurity level rate acted in some elemental metals with low melting temperature in the previous studies. It is expected that the sedimentation of substitutional atoms can be used to control the compositions and structure of alloys or compounds.

Atomic-scale graded structure formed by sedimentation of substitutional atoms in a Bi-Sb alloy

Our compilation of ~900 published results of analyses for minerals of the tetradymite series (tellurobismuthite, tetradymite, guanajuatite, paraguanajuatite, kawazulite, skippenite, tsumoite, hedleyite, pilsenite, laitakarite, ikunolite, joseite-A, joseite-B) allows compositional fields among naturally occurring Bi–Te–Se–S compounds to be established. New compositional data for ingodite, laitakarite, pilsenite, kawazulite and tellurobismuthite extend previously known compositional limits. Recognized minerals can, for the most part, be satisfactorily and conveniently classified according to the ratio Bi(+ Pb)/(Te + Se + S), into the subsystems (isoseries) Bi 2 Te 3 –Bi 2 Se 3 –Bi 2 S 3 , Bi 4 Te 3 –Bi 4 Se 3 –Bi 4 S 3 and BiTe–BiSe–BiS. Most minerals show limited compositional variation, but this is generally more extensive in the Se-bearing phases ( e.g., laitakarite) and in certain members of the system Bi–Te, such as hedleyite and tsumoite. Substitution of minor Pb for Bi is widespread throughout the group, especially in the Bi 4 Te 3 –Bi 4 Se 3 –Bi 4 S 3 subgroup. Several possible additional minerals or compositional variants of existing minerals would appear to exist in nature, including Bi 4 Te 2 Se, Bi 4 Te(Se,S) 2 , Bi 3 Te 2 Se and Bi 3 (Te,S,Se) 4 . Within the above groups, Bi(+ Pb)/(Te + Se + S) stoichiometry is remarkably constant, in accordance with known and derived structures in which all phases (except those in which Pb is essential) can be envisaged in terms of various combinations of nonvalent five-atom Bi 2 X 3 and two-atom Bi 2 layers. Deviation from Bi(+ Pb)/(Te + Se + S) stoichiometry within the isoseries may be linked to stacking disorder. Noting the appearance of many other phases and stoichiometries in experimental work in the system Bi–Te–Se–S and its subsystems, as well as the homologous character of this series, we predict that a significant number of additional mineral phases exist in nature and will be discovered in the future. Many of these, however, cannot be identified by chemical microanalysis alone.

D. Perrin

Papers

Study of the Bi-Sb-Te ternary phase diagram

Study of the n-type Bi2Te2.7Se0.3 doped with bromine impurity

Growth of Bi1 − xSbx alloys by the traveling heater method