Soft rotatory node and structural phase transition in the rare-earth bromo-elpasolites Cs2NaREBr6
- 10 September 1987
- journal article
- Published by IOP Publishing in Journal of Physics C: Solid State Physics
- Vol. 20 (25) , 3809-3821
- https://doi.org/10.1088/0022-3719/20/25/010
Abstract
The structural and dynamical properties of Cs2NaREBr6 (RE=Dy, Ho, Tm) are investigated by neutron scattering and differential scanning calorimetry. Low-energy phonon dispersion curves are measured and analysed with a rigid-ion model. A cubic-to-tetragonal phase transition is observed, and the temperature dependence of the driving rotatory soft mode is determined with a damped harmonic oscillator analysis. The transition temperatures are 101, 126 and 139 K for the Tm, Ho, and Dy elpasolites, respectively. The low-temperature space group is presumably I4/m with a rotation angle of the REBr6 octahedron of approximately 4 deg in Cs2NaHoBr.Keywords
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