An IR spectroscopic investigation of copper manganite CuxMn3−xO4 (O < x <1) spinels and their oxidation products

The IR absorption spectra of tetragonal copper manganite Cu_xMn_3−x O₄ spinels (O < x < 1) have singled out a discontinuity in cation distribution to occur at x > 0.60 in conformity with that recorded by our previous measurements and have warranted the existence of a more complex cation distribution than that proposed earlier. It has been concluded from this study that the ionic configuration for x <0.60, i.e. (Cu_x⁺Mn_1−x²⁺)_A (Mn_2−x³⁺Mn_x⁴⁺)_BO₄²⁻, changes for x > 0.60 to (Cu_x−y⁺Mn_1−x+y²⁺)_A(Cu_y²⁺Mn_2−x−y³⁺Mn_x⁴⁺)_BO₄²⁻, where y represents a low value (less than 0.20).

When the oxidation of Mn²⁺ and Cu⁺ ions is achieved below 450 °C, IR absorption measurements confirm the formation of a cation-deficient metastable spinel phase Cu_1.5Mn_1.5O_4+δ with a 1:3 octahedral superstructure.