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Media type:
E-Article
Title:
Diffuse scattering anisotropy and theP21/a↔A2/aphase transition in titanite, CaTiOSiO4
Contributor:
Malcherek, Thomas;
Paulmann, Carsten;
Domeneghetti, M. Chiara;
Bismayer, Ulrich
Published:
International Union of Crystallography (IUCr), 2001
Published in:
Journal of Applied Crystallography, 34 (2001) 2, Seite 108-113
Language:
Not determined
DOI:
10.1107/s0021889800017763
ISSN:
0021-8898
Origination:
Footnote:
Description:
<jats:p>Diffuse scattering in titanite has been measured at three temperatures, 0.951<jats:italic>T</jats:italic><jats:sub><jats:italic>c</jats:italic></jats:sub>, 1.053<jats:italic>T</jats:italic><jats:sub><jats:italic>c</jats:italic></jats:sub>and 1.177<jats:italic>T</jats:italic><jats:sub><jats:italic>c</jats:italic></jats:sub>, using synchrotron radiation.<jats:italic>T</jats:italic><jats:sub><jats:italic>c</jats:italic></jats:sub>= 487 K is the temperature of the antiferroelectric paraelectric phase transition. Charge-coupled device (CCD) intensity measurements were centred about the \bar{4}01 reciprocal-lattice position (space-group setting<jats:italic>P</jats:italic>2<jats:sub>1</jats:sub>/<jats:italic>a</jats:italic>) and extended beyond the neighbouring \bar{4}11 and \bar{4}\bar{1}1 fundamental positions. Planar diffuse scattering intensity is observed normal to [100] with a lens-shaped maximum centred at \bar{4}01. On approaching<jats:italic>T</jats:italic><jats:sub><jats:italic>c</jats:italic></jats:sub>from above, the intensity of the maximum at \bar{4}01 increases, while intensity scattered into the planes decreases at large distances to the critical zone-boundary position. The intensity distribution is interpreted in terms of a two-dimensional spin-1/2 Ising model, in which individual spin states represent the collective displacement of octahedrally coordinated Ti atoms parallel to [100].</jats:p>