Crystal structure and physical properties of quaternary clathrates Ba{sub 8}Zn{sub x}Ge{sub 46-x-y}Si{sub y}, Ba{sub 8}(Zn,Cu){sub x}Ge{sub 46-x} and Ba{sub 8}(Zn,Pd){sub x}Ge{sub 46-x}

Journal Article · Fri Oct 15 00:00:00 EDT 2010 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2010.07.047· OSTI ID:21421478

Nasir, Navida; Grytsiv, Andriy; Melnychenko-Koblyuk, Nataliya ^[1]; Rogl, Peter ^[1]; Bednar, Ingeborg; Bauer, Ernst ^[2]

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1. Institute of Physical Chemistry, University of Vienna, A-1090 Wien (Austria)
2. Institute of Solid State Physics, Vienna University of Technology, A-1040 Wien (Austria)

Three series of vacancy-free quaternary clathrates of type I, Ba{sub 8}Zn{sub x}Ge{sub 46-x-y}Si{sub y}, Ba{sub 8}(Zn,Cu){sub x}Ge{sub 46-x}, and Ba{sub 8}(Zn,Pd){sub x}Ge{sub 46-x}, have been prepared by reactions of elemental ingots in vacuum sealed quartz at 800 {sup o}C. In all cases cubic primitive symmetry (space group Pm3n, a{approx}1.1 nm) was confirmed for the clathrate phase by X-ray powder diffraction and X-ray single crystal analyses. The lattice parameters show a linear increase with increase in Ge for Ba{sub 8}Zn{sub x}Ge{sub 46-x-y}Si{sub y}. M atoms (Zn, Pd, Cu) preferably occupy the 6d site in random mixtures. No defects were observed for the 6d site. Site preference of Ge and Si in Ba{sub 8}Zn{sub x}Ge{sub 46-x-y}Si{sub y} has been elucidated from X-ray refinement: Ge atoms linearly substitute Si in the 24k site whilst a significant deviation from linearity is observed for occupation of the 16i site. A connectivity scheme for the phase equilibria in the 'Ba{sub 8}Ge{sub 46}' corner at 800 {sup o}C has been derived and a three-dimensional isothermal section at 800 {sup o}C is presented for the Ba-Pd-Zn-Ge system. Studies of transport properties carried out for Ba{sub 8{l_brace}}Cu,Pd,Zn{r_brace}{sub x}Ge{sub 46-x} and Ba{sub 8}Zn{sub x}Si{sub y}Ge{sub 46-x-y} evidenced predominantly electrons as charge carriers and the closeness of the systems to a metal-to-insulator transition, fine-tuned by substitution and mechanical processing of starting material Ba{sub 8}Ge{sub 43}. A promising figure of merit, ZT {approx}0.45 at 750 K, has been derived for Ba{sub 8}Zn{sub 7.4}Ge{sub 19.8}Si{sub 18.8}, where pricey germanium is exchanged by reasonably cheap silicon. - Graphical abstract: Quaternary phase diagram of Ba-Pd-Zn-Ge system at 800 {sup o}C.

• OSTI ID: 21421478
• Journal Information: Journal of Solid State Chemistry, Vol. 183, Issue 10; Other Information: DOI: 10.1016/j.jssc.2010.07.047; PII: S0022-4596(10)00330-0; Copyright (c) 2010 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
BARIUM COMPOUNDS
CHARGE CARRIERS
CLATHRATES
COPPER COMPOUNDS
GERMANIUM COMPOUNDS
LATTICE PARAMETERS
MONOCRYSTALS
PALLADIUM COMPOUNDS
PHASE DIAGRAMS
PHYSICAL PROPERTIES
SILICON COMPOUNDS
SPACE GROUPS
X-RAY DIFFRACTION
ZINC COMPOUNDS
ALKALINE EARTH METAL COMPOUNDS
COHERENT SCATTERING
CRYSTALS
DIAGRAMS
DIFFRACTION
INFORMATION
SCATTERING
SYMMETRY GROUPS
TRANSITION ELEMENT COMPOUNDS