Abstract
The structural transitions of the perovskite KMnF3 are studied with an energy-dispersive X-ray diffractometer. It is found that the 83 K transition is of first order, though the transition related to the condensation of a M3-soft phonon mode is considerably affected by crystallographic domain-walls occurring below the 186 K transition. The latter transition is observed at 88.0 K (first-order), and 92.0 K (second-order) in different single crystals, respectively. The difference of the transition temperature and the transition order is interpreted in terms of inner strains appeared in the domain walls.
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