Effet Jahn-Teller coopératif dans le systéme Mn3O4Mn2SnO4

Mn³⁺ ion (3d⁴, t³_2ge_g¹) is liable to induce, by a cooperative Jahn-Teller effect, a macroscopic distortion of the cubic spinel structure; it is so in haussmanite Mn₃O₄, a tetragonal structure. The effect of chemical composition on “tetragonal-cubic” spinel transformations in the system Mn₃O₄Mn₂SnO₄ has been studied by X-ray diffraction; the c and a′ unit-cell dimensions show an abrupt change at a critical composition beyond which the system has the cubic spinel structure. The cation distribution has been worked out from an analysis of the X-ray diffraction intensities, and a correlation between the number of Mn³⁺ ions in octahedral sites and the degree of distortion has been obtained; the values of “cation-anion” bond distances, in six coordination, show that, in this system, the oxygen octahedral distortion and the macroscopic cell distortion are in a direct relationship. The paramagnetic study always attributes the “high-spin” configuration t³_2ge_g¹ to manganese.