skip to main content

Title: First evidence of P2{sub 1}/n to P2{sub 1}/c structural transformation in pyroxene-type LiAlGe{sub 2}O{sub 6} under high-pressure conditions

The high-pressure behavior of the pyroxene-type compound LiAlGe{sub 2}O{sub 6}, the unique representative of a P2{sub 1}/n-pyroxene, was investigated by in-situ X-ray diffraction and Raman spectroscopy on single-crystal samples hydrostatically pressurized in a diamond-anvil cell. The structure was found to undergo a first-order phase transition on compression, with a critical transition at 5.23±0.02 GPa. Together with a strong volume discontinuity of −ΔV/V{sub 0}=−4.1% the transition shows a remarkable hysteresis loop over at least 0.70 GPa pressure interval. The bulk modulus of the low- and high-pressure polymorphs corresponds to K{sub 0}=114(1) and 123(2) GPa, respectively, as described by a 2{sup nd} order Birch–Murnaghan equation of state. Based on the systematic extinctions the transition was identified as a P2{sub 1}/n-to-P2{sub 1}/c transformation. The mechanism of structural transformation was identified to be controlled by the stereochemistry of the Li atoms at the M2 site, which changes its coordination number from 5 to 6. The formation of new Li–O bonds involves the co-operative folding of Ge{sub 2}O{sub 6}-chains, which explains the anisotropy of axial elasticities and the spontaneous strain across the transformation. Simultaneously the distortion correction of AlO{sub 6} units associated with the transition further explains the preference of the P2{sub 1}/c structure undermore » pressure. - Graphical abstract: Detail of the crystal structures of LP-LAG at 3.48 GPa (left) and HP-LAG at 4.51 GPa (right). Li on M2 are green; AlO{sub 6} octahedra (Al at M1) are orange; tetrahedra sites in LP-LAG: T1 (yellow) and T2 (blue); tetrahedra sites in HP-LAG: A-chains (yellow), B-chains (blue). - Highlights: • A new high-pressure phase transition P2{sub 1}/n–P2{sub 1}/c was found for LaAlGe{sub 2}O{sub 6}. • The transition was also followed by micro-Raman spectroscopy. • The high-pressure polymorph shows a higher bulk modulus. • The structural evolution of the two symmetries was determined.« less
Authors:
 [1] ; ; ;  [2] ; ;  [1] ;  [3]
  1. Department of Geosciences, University of Padua, Via Gradenigo 6, I-35131 Padova (Italy)
  2. Institut für Mineralogie und Kristallographie, Universität Wien, Althanstrasse 14, A-1090 Wien (Austria)
  3. Fachbereich Materialforschung und Physik, Universität Salzburg, Hellbrunnerstrasse 34, A-5020 Salzburg (Austria)
Publication Date:
OSTI Identifier:
22486745
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 228; 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; ALUMINIUM COMPOUNDS; ANISOTROPY; CORRECTIONS; DIAMONDS; ELASTICITY; EQUATIONS OF STATE; GERMANATES; HYSTERESIS; LITHIUM COMPOUNDS; MONOCLINIC LATTICES; MONOCRYSTALS; PHASE TRANSFORMATIONS; PRESSURE DEPENDENCE; RAMAN SPECTROSCOPY; SILICATE MINERALS; STEREOCHEMISTRY; STRAINS; X-RAY DIFFRACTION