Abstract
Electron diffraction experiments reveal a novel phase transition in RbFeF 4 and confirm the existence of phase transitions at 368 K in KFeF 4, at 378 K in RbFeF 4, and at 413 K in RbVF 4. At variance with other studies it is found that the periodicity along the c axis is doubled in the room temperature phase of RbFeF 4 and there is no indication for the disappearance of this doubling at 413 K in RbVF 4. A proposal for the structural characteristics of the phases involved in this transition is made, using the complete list of possible structures obtained when only tilting of rigid octahedra is allowed. Some attention is also paid to decomposition phenomena under electron irradiation.
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