Changes in valency state of ions in CuMn2O4 at high temperatures

Thin films of copper manganite with three different molar ratios of CuMn viz 11, 12 and 13 have been deposited on quartz plates. The electrical conductivity of these thin films has been studied as a function of temperature. The energy of activation for electrical conduction in these compounds is found to increase from 0.20 eV to about 0.62 eV above 600° K. Differential thermal analysis of bulk sample of copper manganite also shows a small endothermic change at 600° K, while thermogravimetric analysis does not show any change in weight. It has been concluded from these results that the stable form of the ionic configuration of copper manganite at low temperatures, i.e. Cu¹⁺Mn³⁺Mn⁴⁺]O₄ changes at high temperatures to Cu²⁺Mn₂ ³⁺]O₄