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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

Abstract

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
Journal Name:
Journal of Solid State Chemistry
Additional Journal Information:
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); Journal ID: ISSN 0022-4596
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

Citation Formats

Nestola, Fabrizio, Artac, Andreas, Pippinger, Thomas, Miletich, Ronald, Secco, Luciano, Milani, Sula, and Redhammer, Günther J. 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. United States: N. p., 2015. Web. doi:10.1016/J.JSSC.2015.05.005.
Nestola, Fabrizio, Artac, Andreas, Pippinger, Thomas, Miletich, Ronald, Secco, Luciano, Milani, Sula, & Redhammer, Günther J. 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. United States. https://doi.org/10.1016/J.JSSC.2015.05.005
Nestola, Fabrizio, Artac, Andreas, Pippinger, Thomas, Miletich, Ronald, Secco, Luciano, Milani, Sula, and Redhammer, Günther J. 2015. "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". United States. https://doi.org/10.1016/J.JSSC.2015.05.005.
@article{osti_22486745,
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},
author = {Nestola, Fabrizio and Artac, Andreas and Pippinger, Thomas and Miletich, Ronald and Secco, Luciano and Milani, Sula and Redhammer, Günther J.},
abstractNote = {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 under 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.},
doi = {10.1016/J.JSSC.2015.05.005},
url = {https://www.osti.gov/biblio/22486745}, journal = {Journal of Solid State Chemistry},
issn = {0022-4596},
number = ,
volume = 228,
place = {United States},
year = {Sat Aug 15 00:00:00 EDT 2015},
month = {Sat Aug 15 00:00:00 EDT 2015}
}