Electrical conductivity, thermogravimetric and differential thermal analysis of manganites of some transition metals

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

Studies of the effect of additions of some elements on the electrical conductivity of strontium titanate

The AC conductivity as a function of temperature was measured in the temperature range of 298-748K at a frequency of 20 kHz for pure and doped SrTiO3. The plots of log sigma showed that all curves had the same feature in common whatever the type or concentration of dopants. The curves possessed two horizontal plateaux where the values of sigma did not change with temperature. There were three linear parts where the conductivity increased as a function of temperature. The values of activation energy for conduction delta E1, delta E2 and delta E3 were calculated for these parts. A further increase of dopants created imperfections

dielectric properties of chromium trioxide and its suboxides

Both the dielectric constant and the dielectric loss of chromium trioxide and some suboxides were measured at different temperatures and various frequencies. It was found that the dielectric constant and the dielectric loss for chromium oxides increased as the temperature increased. The specific electric conductivity for the samples was calculated from the dielectric loss measurements. It was found that the calculated conductivity is in the same order of 10-6 cm-1 as measured by AC conductivity

Infrared spectra of different chromium oxides

Infrared spectra were recorded for eight samples of chromium trioxide and some of its suboxides [CrO3-x, x=0-1.50] which were prepared from the thermal decomposition of CrO2 in a closed system at definite temperature. These are CrO2.88, CrO2.67, CrO2.51, CrO2.46, CrO2.41, CrO1.98 and CrO1.50. X-ray analysis indicates that, each sample contains a single oxidation state of Cr and one crystallographic phase. The infrared absorption measurements declared that the first samples [CrO2 and CrO2.88] represent valence six Cr6 +/- at 906 cm-1. Valency 5+ is quite clear from the absorption bands of CrO2.67, CrO2.51, CrO2.46 and CrO2.41 at 534 and 740 cm-1. In this group the absorption band at 450 cm-1 is very sensitive to changes in oxygen deficiency. The infrared spectra of CrO1.98 and CrO1.50 are coincident with those obtained for Cr4+ and Cr3+, respectively