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Structure and phase transitions of CaTaOAlO 4
Author(s) -
Malcherek Thomas,
Borowski Markus,
Bosenick Anne
Publication year - 2004
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s002188980302689x
Subject(s) - rietveld refinement , monoclinic crystal system , powder diffraction , crystallography , diffraction , chemistry , crystal structure , phase transition , spectroscopy , space group , infrared spectroscopy , lattice (music) , x ray crystallography , materials science , condensed matter physics , physics , optics , organic chemistry , quantum mechanics , acoustics
The structure of CaTaOAlO 4 (CTAO) has been determined using X‐ray powder diffraction and density functional methods in combination with 27 Al MAS NMR spectroscopy. A structural phase transition occurs near room temperature in CTAO as indicated by heat‐capacity measurements, lattice strain data and infrared spectroscopy. Rietveld analysis of the powder diffraction data does not indicate deviation from monoclinic symmetry C 2/ c . But the observed quadrupolar coupling of the Al atom is reproduced by the electronic structure calculations only in a structure with space‐group symmetry P 2 1 / n , distinguished by two different Ta coordination environments. The atomic coordinates of this low‐temperature structure of CTAO are obtained by computational force relaxation within the experimental unit cell determined at 170 K.