Abstract
The beryllides = rare earths and actinides) crystallize in a -type cubic structure, which can be categorized as a cage-structured compound. In this study, powder x-ray diffraction measurements have been performed on , and in the temperature range between 7 and 300 K in order to investigate their crystallographic characteristics systematically. They keep the -type cubic structure down to the lowest temperature. We estimated their Debye temperature to be 600–750 K from analyses of the temperature dependence of a lattice parameter, being in good agreement with the values reported previously. Rietveld refinements on the obtained powder patterns revealed that the atom in the site is located in an almost ideal snub cube formed by atoms in the site, whose caged structure is unchanged even at the low temperatures. In addition, it is argued from the temperature variation of an isotropic mean-square displacement parameter that the compounds commonly have a low-energy phonon mode, which can be described by a model assuming an Einstein oscillation of the atom with a characteristic temperature of K.
- Received 10 November 2017
- Revised 2 April 2018
DOI:https://doi.org/10.1103/PhysRevMaterials.2.053603
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