Department of Chemistry, Indian Institute of Technology. Bombay 400076 The structural properties of spinet-like manganites, particularly those of copper and magnesium have been described. The distribution of the cations over the tetrahedral and octahedral sites in the lattice have been deter­mined by neutron diffraction. The advantage of this technique and the indeterminacy of the earlier X-ray results have been pointed out. The present study indicates that copper manganite is a cubic spinel

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... ch is about 25 percent inverted. It has been possible to assign the structural formula (Cu2+.50 Cu1+.25 Mn3+.25) [Cu2+.25 Mn31+.50 Mn4+.25]O24-, which satsifactorily explains the observed properties of the compound. The Mg2+ ions in magnesium manganite, normally present in the tetrahedral sites migrate partially to the octahedral site on thermal treatments. The activation energy for this migration has been found to be 0.29 eV. The results obtained from the x-ray and the neutron diffraction methods for Mg2+ [Mn3+2]O4 have also been compared.