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The crystal structure of KCaF3 at 4.2 and 300 K: A re-evaluation using high-resolution powder neutron diffraction

Published online by Cambridge University Press:  01 March 2012

K. S. Knight,
C. N. W. Darlington and
I. G. Wood
K. S. Knight*
Affiliation:
ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon., OX11 0QX, United Kingdom and Department of Mineralogy, The Natural History Museum, Cromwell Road, London, SW7 5BD, United Kingdom
C. N. W. Darlington
Affiliation:
School of Physics and Astronomy, University of Birmingham, Birmingham, B15 2TT, United Kingdom
I. G. Wood
Affiliation:
Department of Earth Sciences, University College London, Gower Street, London, WC1E 6BT, United Kingdom
*
a)Electronic mail: k.s.knight@rl.ac.uk
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Abstract

The crystal structure of the perovskite phase KCaF3 has been redetermined at 4.2 and 300 K using powder neutron diffraction collected at the highest resolution. At both temperatures the phase was found to be orthorhombic in space group Pnma, with lattice parameters a=0.622 879(5) nm, b=0.870 031(7) nm, c=0.611 210(5) nm at 4.2 K, and a=0.621 488(6) nm, b=0.876 360(8) nm, c=0.616 481(6) nm at 300 K. The CaF6 octahedron is regular at both temperatures with octahedral rotations of 9.6° and 13.2° for the in-phase and anti-phase tilts, respectively, at 4.2 K. No evidence was found to support the recent revision of the space group from Pnma to the monoclinic space group B21∕m.

Keywords

powder neutron diffractionRietveld profile refinementKCaF3

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Type
Technical Articles
Information
Powder Diffraction , Volume 20 , Issue 1 , March 2005, pp. 7 - 13
Copyright
Copyright © Cambridge University Press 2005

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