Jahn-Teller Effects on Mössbauer Spectra of Fe₅₇ in FeCr₂O₄ and FeV₂O₄

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Mössbauer spectra of FeCr₂O₄ and FeV₂O₄, which undergo the cubic-to-tetragonal transition at 135°K and 140°K respectively, have been measured in the temperature range from liquid nitrogen to room temperature. Quadropole splittings have been observed even above the distortion temperature. Each line of the Mössbauer spectra becomes broadest at the transition temperature. These temperature dependence of the Mössbauer spectra can be explained qualitatively on the basis of the simple model of a motional narrowing phenomenon.