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

Some dielectric properties of strontium titanate doped with some metal oxides.

SrTio3 and SrTiO3 doped with CeO2, Gd2O3 and CuO were prepared according to the recommended procedure using the ceramic method. The doping concentrations ranged from 0.5 to 5 mole% and the prepared materials were structurally investigated by X-ray diffraction and IR absorption spectrum. The dielectric constant and loss were measured within the frequency band 105 to 107 Hz and the temperature range from 20 to 50 degree. The dielectric relaxation proces and its thermodynamic parameters, the activation enthalpy and the entropy changes [delta H epsilon and delta S epsilon] were calculated using the usual rate equations. The results were correlated with the structure of the titanates and the effect of doping was discussed

Infrared absorption spectra of pure and doped SrTiO[3]

The infrared absorption spectra of pure SrTiO[3] and when doped by CuO, Gd[2]O[3] or CeO[2] with different concentrations namely [0.5, 1.0, 3.0, and 5.0 Mole percent] have been measured. The I.R absorption measurements in the range 200-4000 cm[-1] revealed two main absorption bands in the ranges 380-400 cm[-1] and 540-610 cm[-1], which were assigned to two TiO[6] octahedral normal modes. Some bands at 217, 237 and 260 cm[-1] which were due to cation-TiO[3] vibration are also observed. Two absorption bands at 1020, 1100 cm of higher intensities were observed due to metal-oxygen bond. The main bands still present in all samples with slight shift and broadening in band positions with increasing dopant concentrations which favour the formation of the tetragonal modification