Structure and Thermoelectric Properties of Ba6Ge25−x, Ba6Ge23Sn2, and Ba6Ge22In3: Zintl Phases with a Chiral Clathrate Structure

• Published in: Journal of solid state chemistry Vol. 153; no. 2; pp. 321 - 329
• Main Authors: Kim, Sung-Jin, Hu, Siqing, Uher, Ctirad, Hogan, Tim, Huang, Baoquan, Corbett, John D., Kanatzidis, Mercouri G.
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 01.09.2000; Elsevier
• Subjects: chiral clathrate; Clusters, nanoparticles, and nanocrystalline materials; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Conductivity phenomena in semiconductors and insulators; electron crystal; Electronic transport in condensed matter; Exact sciences and technology; Nanoscale materials: clusters, nanoparticles, nanotubes, and nanocrystals; phonon gas; Physics; Structure of solids and liquids; crystallography; thermoelectric; Thermoelectric and thermomagnetic effects; zintl phase; zintl phase; phonon gas; thermoelectric; chiral clathrate; electron crystal; Tin compounds; Inorganic compounds; Electrical conductivity; Barium compounds; Barium Germanides; Seebeck effect; XRD; Experimental study; Germanium compounds; Clathrates; Thermoelectric properties; Germanium Molecules; Tin Germanides; Thermal conductivity; Chiral symmetry; Indium Germanides; Indium compounds; Atomic clusters; Zintl phases; Crystal structure
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1006/jssc.2000.8777

A single phase of Ba6Ge25−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. Ba6Ge25−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 Ba6Ge25−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 ∼100 K. Ba6Ge23.32Sn1.68 and Ba6Ge21.93In3.07 as ternary derivatives of Ba6Ge25−x were also synthesized and their structural and physical properties compared with those of Ba6Ge25−x.