Two-dimensional structural phase transitions of RBFeF4and CsFeF4
- 28 May 1979
- journal article
- Published by IOP Publishing in Journal of Physics C: Solid State Physics
- Vol. 12 (10) , 1799-1807
- https://doi.org/10.1088/0022-3719/12/10/012
Abstract
New structural phase transitions in RbFeF4 and CsFeF4 have been discovered by specific heat, optical observations, dielectric constant measurements and by X-ray diffraction studies. RbFeF4 was found to have a first-order transition at 105 degrees C and a second-order transition at 145 degrees C. CsFeF4 was found to have a second-order transition at 150 degrees C and a first-order transition at 235 degrees C. These transitions can be accounted for by a simple model based on the rotation of FeF6 octahedra around the crystallographic (100) and (010) directions. The structures have been determined for each of these phases, suggesting that the transitions may be related to the condensation, at the X zone-boundary points of tetragonal phase, of soft-phonon modes of B2g and B3g symmetry and wavevector q=(1/2, 0, 0) and q=(0, 1/2, 0) respectively.Keywords
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