Cooperative Jahn-Teller Distortions in the Systems ZnMn2O4–Cu2GeO4 and ZnMn2O4–ZnCuGeO4

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Abstract
Ionic distributions and cooperative J‐T (Jahn‐Teller) distortions are studied in the systems ZnMn2O4–Cu2GeO4 and ZnMn2O4–ZnCuGeO4 which contain both Cu2+ and Mn3+ ions. Cation distributions were determined by x‐ray diffraction for Zn0.5Cu0.5[Ge0.5Cu0.5Mn]O4 and by neutron diffraction for Zn[CuGe]O4. The ionic distributions for the two systems were then taken to be Zn1−xCux [GexCuxMn2−2x]O4 and Zn[GexCuxMn2−2x]O4. In the first system, the axial ratio c/a was found to depend essentially on the Mn3+ content only. The equal distribution of the Cu2+ ions over the A and B lattice sites results in the apparent neutralization of contributions from Cu2+ ions to cooperative J‐T distortions. In the second system J‐T distortions at room temperature were observed to much lower concentrations of Mn3+ ions than for the first system. However, in spite of most of the Cu2+ ions being on the B sites, the Zn[CuGa]O4 end of the system was found to be cubic at room temperature. The cation distribution was determined with x‐ray diffraction for Ga[CuGa]O4 which is also cubic.

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