Cs(Be₂Li)Al₂Si₆O₁₈, a cesium-stuffed host-guest structure, and its structure-property variations with temperature and pressure

Author(s)

Martin Ende, Giacomo Diego Gatta, Paolo Lotti, Alexander Grandtner, Ronald Miletich

Abstract

The solid-state structure of (Cs,Na)[(Be2Li)Al2Si6O18], a beryl-type material, was studied in-situ on single crystal and powder samples at hydrostatic high pressure conditions (P <= 9.8 GPa) as well as under temperature variation (83<= T <= 1173 K) by means of Raman spectroscopy, X-ray and synchrotron diffraction. The investigations show an inconspicuous, easily overlooked transformation from R3c to non-centrosymmetric R3c space-group symmetry on increasing pressure (Pc ~ 4 GPa) and decreasing temperature (Tc ¼ 312 5 K), as revealed by Raman band splitting as well as discontinuities in the evolution of Raman spectra, thermal expansivity coefficients and anomalous compression behavior. Distortions to acentric symmetry originate from the Cs and Na guest atoms inside the channels parallel the c-axis. The occurrence of diffuse scattering planes in all measured data sets indicates substitutional defects inside the channels following an approximate ~4.6 Å periodicity, without any remarkable ordering between adjacent channels. The determined thermal expansivity follows an inverse behavior compared to other beryl-type structures for the R3c phase. The bulk moduli for the two polymorphs compare, together with the observed compressional anisotropy, to other complex beryl-type framework structures. However, the symmetry reduction at high pressure leads to independent displacements of the framework oxygen positions, and as a consequence, to the increase of the coordination number from [6 þ 6] to [6 þ 9] for one of the Cs sites.

Organisation(s)

Department of Mineralogy and Crystallography

External organisation(s)

Università degli Studi di Milano-Bicocca

Journal

Journal of Solid State Chemistry

Volume

293

No. of pages

11

ISSN

0022-4596

DOI

https://doi.org/10.1016/j.jssc.2020.121841

Publication date

01-2021

Peer reviewed

Yes

Austrian Fields of Science 2012

104026 Spectroscopy, 105116 Mineralogy, 105113 Crystallography, 104024 X-ray structural analysis

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/60e66ec9-416b-479c-b9dc-d1dbad010567