Ba{sub 6}Ge{sub 25}: low-temperature Ge-Ge bond breaking during temperature-induced structure transformation

Journal Article · Tue Mar 15 00:00:00 EST 2005 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2004.11.011· OSTI ID:20725828

Carrillo-Cabrera, Wilder ^[1]; Borrmann, Horst ^[1]; Paschen, Silke ^[1]; Baenitz, Michael ^[1]; Steglich, Frank ^[1]; Grin, Yuri ^[1]

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1. Max-Planck-Institut fuer Chemische Physik fester Stoffe, Noethnitzer Str. 40, D-01187 Dresden (Germany)

In order to find the optimal conditions for sample preparation of the binary germanide Ba{sub 6}Ge{sub 25}, the germanium-rich part of the Ba-Ge phase diagram was redetermined by means of metallography, X-ray powder diffraction and differential thermal analysis. The temperature behavior of cubic Ba{sub 6}Ge{sub 25} was investigated both on polycrystalline samples and single crystals. The temperature dependence of the lattice parameter exhibits two anomalies at about 180 and 230K, respectively, which are caused by a structure transformation in two steps with hysteresis. Powder (T=10-295K) and single-crystal (T=95-295K) X-ray diffraction studies confirm that the symmetry of Ba{sub 6}Ge{sub 25} (space group P4{sub 1}32) remains unchanged within the entire temperature range. A reconstructive behavior of the structural transformation is observed, involving Ge-Ge bond breaking and barium cation displacements. Some Ge4 type atoms ({approx}28%) are so significantly displaced during cooling that Ge4-Ge6 bonds break and new three-bonded (3b)Ge{sup -} species (electron acceptors) are formed. Consequently, the number of charge carriers is reduced, affecting the physical properties. The reversible bond breaking involved in this process is a typical characteristic of a solid-state chemical reac0010ti.

• OSTI ID: 20725828
• Journal Information: Journal of Solid State Chemistry, Vol. 178, Issue 3; Other Information: DOI: 10.1016/j.jssc.2004.11.011; PII: S0022-4596(04)00611-5; Copyright (c) 2004 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

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
BARIUM COMPOUNDS
BINDING ENERGY
CHARGE CARRIERS
CUBIC LATTICES
DIFFERENTIAL THERMAL ANALYSIS
GERMANIDES
GERMANIUM IONS
HYSTERESIS
LATTICE PARAMETERS
METALLOGRAPHY
MONOCRYSTALS
PHASE DIAGRAMS
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
POLYCRYSTALS
SAMPLE PREPARATION
SPACE GROUPS
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE 0065-0273 K
X-RAY DIFFRACTION