Structural phase transition of KMF4(M=Fe, V, Ti)

Abstract
New structural phase transitions of KMF4 (M=Fe, V, Ti) have been observed from dielectric constant measurements and from X-ray diffraction studies. KFeF4 was found to have two phase transitions, one of second order at 95 degrees C and another of first order at 290 degrees C. KVF4 and KTiF4 were found to have first-order transitions at 255 degrees C and 215 degrees C respectively. These transitions can be explained by the rotations of MF6 octahedra about the (100) and (010) axes, and are related to the condensation of zone boundary soft-phonon modes in the higher symmetry phase.

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