First evidence of <i>P</i>2<i>1/n</i> to <i>P</i>2<i>1/c</i> structural transformation in pyroxene-type LiAlGe₂O₆ under high-pressure conditions

Author(s)

Fabrizio Nestola, Andreas Artac, Thomas Pippinger, Ronald Miletich-Pawliczek, Luciano Secco, Sula Milani

Abstract

The high-pressure behavior of the pyroxene-type compd. LiAlGe2O6, the unique representative of a P21/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 crit. transition at 5.23±0.02 GPa. Together with a strong vol. discontinuity of -V/V0=-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 K0=114(1) and 123(2) GPa, resp., as described by a 2nd order Birch-Murnaghan equation of state. Based on the systematic extinctions the transition was identified as a P21/n-to-P21/c transformation. The mechanism of structural transformation was identified to be controlled by the stereochem. of the Li atoms at the M2 site, which changes its coordination no. from 5 to 6. The formation of new Li-O bonds involves the co-operative folding of Ge2O6-chains, which explains the anisotropy of axial elasticities and the spontaneous strain across the transformation. Simultaneously the distortion correction of AlO6 units assocd. with the transition further explains the preference of the P21/c structure under pressure.

Organisation(s)

Department of Mineralogy and Crystallography

External organisation(s)

University of Padova, Universität Bayreuth

Journal

Journal of Solid State Chemistry

Volume

228

Pages

250-257

No. of pages

8

ISSN

0022-4596

DOI

https://doi.org/10.1016/j.jssc.2015.05.005

Publication date

06-2015

Peer reviewed

Yes

Austrian Fields of Science 2012

104011 Materials chemistry, 105113 Crystallography

Keywords

ASJC Scopus subject areas

Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Ceramics and Composites, Materials Chemistry, Inorganic Chemistry, Physical and Theoretical Chemistry

Portal url

https://ucrisportal.univie.ac.at/en/publications/first-evidence-of-p21n-to-p21c-structural-transformation-in-pyroxenetype-lialge2o6-under-highpressure-conditions(e71e3b3d-30cc-45dc-9096-08b943f01819).html