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Title: High-pressure crystallography and compression behavior of the alkali-scandium-germanate end-members LiScGe{sub 2}O{sub 6} and NaScGe{sub 2}O{sub 6}

Synthetic single-crystal samples of the monoclinic pyroxene-type compounds LiScGe{sub 2}O{sub 6} and NaScGe{sub 2}O{sub 6} have been investigated by means of in-situ high-pressure Raman spectroscopy and X-ray diffraction techniques. Crystal-structure investigations at hydrostatic high-pressure conditions were carried out in addition to 10{sup −4} GPa measurements using the diamond-anvil cell technique up to ∼9.5 GPa. Both samples, LiScGe{sub 2}O{sub 6} (space group P2{sub 1}/c, a=9.9999(8) Å, b=9.1040(2) Å, c=5.4610(2) Å, β=109.240(2)° at 10{sup −4} GPa) and NaScGe{sub 2}O{sub 6} (space group C2/c, a=10.1678(5) Å, b=9.1583(5) Å, c=5.5672(3) Å, β=107.257(3)° at 10{sup −4} GPa), did not undergo any compression-induced change of symmetry as confirmed by single-crystal diffraction patterns. Series of high-pressure Raman spectra confirm the absence of any symmetry-related structural phase transition with band positions shifting in a smooth fashion on increasing pressure. High-precision lattice parameters, as determined from X-ray diffraction profile analyzes, were used to monitor both the compressibilities of lattice directions and the evolution of the unit-cell volume with pressure. The experimental data was fitted using a third-order Birch–Murnaghan equation-of-state approach and parameterized fits yield V{sub 0}=469.60(11) Å{sup 3}, K{sub 0}=85.6(1.3) GPa and K′=5.9(4) for LiScGe{sub 2}O{sub 6} and V{sub 0}=495.95(19) Å{sup 3}, K{sub 0}=79(3) GPa and K′=3.9(1.1) for NaScGe{submore » 2}O{sub 6}. The systematic comparison of volume properties and compression behavior shows that both pyroxene-type compounds follow established trend lines with similar slopes in comparing volumes versus bulk moduli, and confirm that the position of trend lines in this systematics describing variations with M1 critically depend on the type of M2 and T cations, independent on the space-group symmetry. - Graphical abstract: Polyhedral model of the LiScGe{sub 2}O{sub 6} crystal structure at 9.51 GPa. Red and blue: crystallographic distinctive germanium-tetrahedral chains; Green: scandium-octahedral chains; Purple: lithium atoms. - Highlights: • High-quality high-pressure data of previously uninvestigated germanate compounds. • Results confirmed through complementing sXRD with Raman spectroscopy. • Comparison and relation of high-pressure pyroxene-type compounds.« less
Authors:
 [1] ;  [2] ; ;  [1] ;  [3] ;  [1]
  1. Institut für Mineralogie und Kristallographie, Universität Wien, Althanstrasse 14, A-1090 Wien (Austria)
  2. (Switzerland)
  3. Fachbereich Materialforschung und Physik, Universität Salzburg, Hellbrunnerstrasse 34, A-5020 Salzburg (Austria)
Publication Date:
OSTI Identifier:
22486764
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 229; Other Information: Copyright (c) 2015 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; COMPARATIVE EVALUATIONS; COMPRESSIBILITY; COMPRESSION; EQUATIONS OF STATE; FLUX SYNTHESIS; GERMANATES; LATTICE PARAMETERS; LITHIUM COMPOUNDS; MONOCLINIC LATTICES; MONOCRYSTALS; PHASE TRANSFORMATIONS; RAMAN SPECTRA; RAMAN SPECTROSCOPY; SCANDIUM COMPOUNDS; SILICATE MINERALS; SODIUM COMPOUNDS; X-RAY DIFFRACTION