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Title: Clathrate formation in the systems Sr–Cu–Ge and (Ba,Sr)–Cu–Ge

In the ternary system Sr–Cu–Ge, a novel clathrate type-I phase was detected, Sr{sub 8}Cu{sub x}Ge{sub 46−x} (5.2≤x<5.4), which exists close to the Zintl limit in a small temperature interval. Sr{sub 8}Cu{sub 5.3}Ge{sub 40.7} decomposes eutectoidally on cooling at 730±3 °C into (Ge), SrGe{sub 2} and τ{sub 1}-SrCu{sub 2−x}Ge{sub 2+x}. Phase equilibria at 700 °C have been established for the Ge rich part and are characterized by the appearance of only one ternary compound, τ{sub 1}-SrCu{sub 2−x}Ge{sub 2+x}, which crystallizes with the ThCr{sub 2}Si{sub 2} structure type and forms a homogeneity range up to x=0.4 (a=0.42850(4), c=1.0370(1) nm). Additionally, the extent of the clathrate type-I solid solution Ba{sub 8−y}Sr{sub y}Cu{sub x}Ge{sub 46−x} (0≤y≤∼5.6; 5.2≤x≤5.4, from as cast alloys) has been studied at various temperatures. The clathrate type-I crystal structure (space group Pm3{sup ¯}n) has been proven by X-ray single crystal diffraction on two single crystals with the composition (from refinement): Sr{sub 8}Cu{sub 5.36}Ge{sub 40.64} (a=1.06368(2) nm at 300 K) and Ba{sub 4.86}Sr{sub 3.14}Cu{sub 5.36}Ge{sub 40.64} (a=1.06748(2) nm at 300 K) measured at 300, 200 and 100 K. From the temperature dependence of the lattice parameters and the atomic displacement parameters, thermal expansion coefficients, Debye- and Einstein-temperatures and the speed of soundmore » have been determined. From heat capacity measurements of Sr{sub 8}Cu{sub 5.3}Ge{sub 40.7} at low temperatures the Sommerfeld coefficient (γ=24 mJ/mol K{sup 2}) and the Debye temperature (Θ{sub D}{sup LT}=273 K) have been extracted. From a detailed analysis of these data at higher temperatures, Einstein branches of the phonon dispersion relation have been derived and compared to those obtained from the atomic displacement parameters. Electrical resistivity measurements of Sr{sub 8}Cu{sub 5.3}Ge{sub 40.7} reveal a rather metallic behavior in the low temperature range (<300 K). Density function theory calculations provide densities of states, electronic resistivity and Seebeck coefficient as well as the vibrational spectrum and specific heat. - Graphical abstract: Clathrate type-I unit cell including the coordination polyhedra for the Sr (or Ba) atoms. - Highlights: • A new Sr-based clathrate type-I compound Sr{sub 8}Cu{sub 5.3}Ge{sub 40.7} has been prepared. • The solid solution Ba{sub 8−x}Sr{sub x}Cu{sub ∼5.3}Ge{sub 40.7} has been investigated. • Physical properties of Sr{sub 8}Cu{sub 5.3}Ge{sub 40.7} were measured at low temperatures. • DFT calculations have been performed.« less
Authors:
;  [1] ;  [2] ;  [1] ;  [2] ;  [1] ;  [2] ;  [3] ;  [1] ;  [1]
  1. Institute of Physical Chemistry, University of Vienna, Währingerstr. 42, A-1090 Wien (Austria)
  2. Institute of Solid State Physics, Vienna University of Technology, Wiedner Hauptstrasse 8-10, A-1040 Wien (Austria)
  3. Institute of Mineralogy and Crystallography, University of Vienna, Althanstrasse14, A-1090 Wien (Austria)
Publication Date:
OSTI Identifier:
22443400
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 217; Other Information: Copyright (c) 2014 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ALLOYS; CLATHRATES; COMPARATIVE EVALUATIONS; CUBIC LATTICES; DEBYE TEMPERATURE; DENSITY; DENSITY OF STATES; DISPERSION RELATIONS; ELECTRIC CONDUCTIVITY; LATTICE PARAMETERS; MONOCRYSTALS; PHASE DIAGRAMS; SOLID SOLUTIONS; SPACE GROUPS; SPECIFIC HEAT; SPECTRA; TEMPERATURE DEPENDENCE; THERMAL EXPANSION; X-RAY DIFFRACTION