Abstract
Thermal expansion measurements of polycrystalline, single crystalline and textured specimens Mn x Fe 3− x O 4 are reported. The experimental data are interpreted in terms of two cation migration processes, namely the cation exchange between the octahedral and tetrahedral sublattices, and an octahedral Mn 3+ clustering. The changes in the crystal structure of cubic Mn 1·9Fe 1·1O 4 in the temperature range of 250–350°C indicate a shift in the cation distribution of 0·15–0·20 ions per unit AB 2O 4, which is stabilised by the macroscopic tetragonal distortion of the lattice. The tetragonal distortions of the specimens x=1·9 in combination with electrical conductivity measurements on x=2·0 reveals unequivocally that in the spinel structure octahedral Mn 3+ and Fe 2+ are the stable cation valencies at low temperatures.
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