FORMATION OF COPPER-MANGANESE OXIDES FROM CUXMN1-X(HCOO)(2)CENTER-DOT-2H(2)O MIXED-CRYSTALS

It has been established that two series of mixed crystals are formed i n the Cu(HCOO)(2)-Mn(HCOO)(2)-2H(2)O system at 25 degrees C. The therm al decompositions of CuxM1-x(HCOO)(2) . 2H(2)O mixed crystals (0 less than or equal to x less than or equal to 0.5) have been studied. On th e basis of the methods used (TG, DTA, and X-ray diffraction analysis), it has been established that homogeneous and heterogeneous oxide phas es are obtained depending on the x-values. At about 300 degrees C the formates decompose to Mn5O8 (x = 0); Cu0.4Mn4.6O8 (x = 0.08); a mixtur e of Cu0.4Mn4.6O8 and Cu-1.5 Mn1.5O4 with a different ratio (0.08 < x < 0.5), and a Cu1.5Mn1.5O4 spinel (x = 0.5). Cu0.4Mn4.6O8 (Cu0.42+Mn0. 42+Mn34+O8) crystallizes in the monoclinic system with lattice paramet ers a b = 5.729(4)Angstrom. c = 4.862(5)Angstrom, beta = 109.4 degrees and space group C2/m. At about 600 degrees C the oxides obtained tran sform into alpha-Mn2O3 (x = 0) and a mixture of alpha-Mn2O3 and Cu1.5M n1.5O4 with a different ratio (0 < x < 0.5). The slowly cooled specime n shows a fine structure in the IR spectrum due to the 1:3 ordering of the ions on the B-sublattice, and the cation valences are Cu+ [Cu0.52 +Mn4.54+]O-4. The magnetic measurements show that the oxides obtained are paramagnetic in the temperature range of 25-300 degrees C, and the 1/(chi) versus T curves obey the Curie-Weiss law. The theoretical and experimental magnetic moments of the oxides are given. They coincide well in the case of the homogeneous samples. (C) 1997 Academic Press.