Phase stability, structures and properties of the (Bi{sub 2}){sub m} (Bi{sub 2}Te{sub 3}){sub n} natural superlattices
- Institute of Chemical Sciences and Centre for Advanced Energy Storage and Recovery, Heriot-Watt University, Edinburgh, EH14 4AS (United Kingdom)
- School of Chemistry and Centre for Science at Extreme Conditions, University of Edinburgh, West Mains Road, Edinburgh, EH9 3JJ (United Kingdom)
The phase stability of the (Bi{sub 2}){sub m} (Bi{sub 2}Te{sub 3}){sub n} natural superlattices has been investigated through the low temperature solid state synthesis of a number of new binary Bi{sub x}Te{sub 1-x} compositions. Powder X-ray diffraction revealed that an infinitely adaptive series forms for 0.44{<=}x{<=}0.70, while an unusual 2-phase region with continuously changing compositions is observed for 0.41{<=}x{<=}0.43. For x>0.70, mixtures of elemental Bi and an almost constant composition (Bi{sub 2}){sub m} (Bi{sub 2}Te{sub 3}){sub n} phase are observed. Rietveld analysis of synchrotron X-ray powder diffraction data collected on Bi{sub 2}Te (m=2, n=1) revealed substantial interchange of Bi and Te between Bi{sub 2} and Bi{sub 2}Te{sub 3} blocks, demonstrating that the block compositions are variable. All investigated phase pure compositions are degenerate semiconductors with low residual resistivity ratios and moderate positive magnetoresistances (R/R{sub 0}=1.05 in 9 T). The maximum Seebeck coefficient is +80 {mu}V K{sup -1} for x=0.63, leading to an estimated thermoelectric figure of merit, zT=0.2 at 250 K. - Graphical abstract: An infinite number of possible (Bi{sub 2}){sub m} (Bi{sub 2}Te{sub 3}){sub n} structures exist for Bi{sub x}Te{sub 1-x} compositions between x=0.44 and x=0.70. Compositions near x=2/3 are promising p-type thermoelectrics. Highlights: Black-Right-Pointing-Pointer Phase Stability of the (Bi{sub 2}){sub m}{center_dot}(Bi{sub 2}Te{sub 3}){sub n} Natural Superlattices. Black-Right-Pointing-Pointer Thermoelectric Properties in the Bi{sub x}Te{sub 1-x} Phase Diagram. Black-Right-Pointing-Pointer Crystal Structure of Bi{sub 2}Te from Synchrotron X-ray Powder Diffraction.
- OSTI ID:
- 22149793
- Journal Information:
- Journal of Solid State Chemistry, Vol. 193; Other Information: Copyright (c) 2012 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
- Country of Publication:
- United States
- Language:
- English
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