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Crystal Chemistry and Phase Transitions in Substituted Pollucites along the CsAlSi 2 O 6 ‐CsTiSi 2 O 6.5 Join: A Powder Synchrotron X‐ray Diffractometry Study
Author(s) -
Xu Hongwu,
Navrotsky Alexandra,
Balmer M. Lou,
Su Yali
Publication year - 2002
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.2002.tb00251.x
Subject(s) - tetragonal crystal system , crystallography , crystal structure , synchrotron , rietveld refinement , space group , materials science , x ray crystallography , phase transition , phase (matter) , crystal (programming language) , chemistry , diffraction , condensed matter physics , physics , organic chemistry , nuclear physics , optics , programming language , computer science
The crystal structures for a suite of substituted pollucites with the compositions CsTi x Al 1– x Si 2 O 6+0.5 x , 0 ≤ x ≤ 1, have been determined from Rietveld analysis of powder synchrotron XRD data. Our results indicate that the pollucite end member (CsAlSi 2 O 6 ) has a tetragonal structure (space group I 4 1 / a ), whereas all other compositions are cubic (space group Ia 3 d ). The increased symmetry for the titanium‐substituted structures is presumably due to the incorporation of additional O 2− anions (needed for compensating the charge imbalance between Ti 4+ and Al 3+ ), which effectively holds open the expanded cubic framework. In situ cooling experiments of the substituted phase CsTi 0.1 Al 0.9 Si 2 O 6.05 reveal a displacive transformation to the tetragonal structure at ∼230 K. This transformation is tricritical in nature and is analogous to the tetragonal‐to‐cubic transition in pollucite on heating.