Abstract
A single phase of Ba6Ge(25-x) (x ~ 1) was obtained from a direct element combination reaction in a sealed graphite tube at 830°C. Its structure was determined by single-crystal X-ray diffraction methods. Ba6Ge(25-x) adopts the chiral cubic space group P4132 (No. 213) with dimensions of a = 14.5483(2) Å and Z = 4. The structure consists of helical chains of Ba atom-centered pentagonal dodecahedra, Ba@Ge20, and zeolite-like cages formed by those chains. There are vacancies distributed over the Ge sites giving a composition of Ba6Ge24, in which charge balance according to the Zintl formalism is retained. The compound therefore satisfies the classical Zintl concept. Polycrystalline ingots of Ba6Ge(25-x) showed an electrical conductivity of 2000 S/cm and a Seebeck coefficient of - 18 μV/K at room temperature. An anomalous broad transition in the electrical conductivity and Seebeck coefficient was observed at Å 100 K. Ba6Ge23.32Sn1.68 and Ba6Ge21.93In3.07 as ternary derivatives of Ba6Ge(25-x) were also synthesized and their structural and physical properties compared with those of Ba6Ge(25-x). (C) 2000 Academic Press.
Original language | English |
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Pages (from-to) | 321-329 |
Number of pages | 9 |
Journal | Journal of Solid State Chemistry |
Volume | 153 |
Issue number | 2 |
DOIs | |
State | Published - 2000 |
Bibliographical note
Funding Information:Financial support from DARPA through the Army Research O$ce (DAAG55-97-1-0184) and the Center for Fundamental Materials Research are greatefully acknowledged. S.-J.K. also acknowledges "nancial support from the Korean Ministry of Education (BSRI 96-3413).
Keywords
- Chiral clathrate
- Electron crystal
- Phonon gas
- Thermoelectric
- Zintl phase