RESUMO
Different samples of some manganite of cobalt, nickel, copper, and zinc were prepared and subjected to thermal analyses and electrical conductivity measurements. Thermogravimetric analysis showed a thermal stability of the system from 150 degree C up to 500 degree C. the DTA curves indicated that there is no change in phase as a function of temperature. The a.c. conductivity as a function of temperature range 25-390 degree C showed that all the prepared samples behave as semi conductor materials. There are a distinct change in the slop [knee]for all samples, The samples of formula with X=1 contain the least impurity content. Diffuse reflectance measurements show a common absorption at 3.53 [eV] which is independent on the sample composition. From the result it may be canceled that adding Co, Ni, Cu and Zn ion to Mn2O3 almost exhibits nochange in the structure of the spinel
RESUMO
Infared spectra of inorganic solids not only reveal the characteristic vibrational and stretching frequencies of the bonded atoms within molecules, but also indicate the difference modes of transition occurring either by electrons or optical phonones in the lattice when the range of spectra is extended to the far infrared. In spite of the large amount of literature about the semi conducting properties of bismuth chalcogenides, little work was done to disclose the characteristics of these compounds[1,3] This article deals with some of these properties in order to throw more light on the physicochemical behaviour of bismuth chalcogenides