SAID SHEHATA

The electrical properties of some copper-containing phosphate glasses were studied. The electrical conductivity value for all studied glasses were presented at room temperature and Cu +/Cu tot ratios. The conductivities of ternary glasses MgO-, CaO-, ZnO- and PbO-containing copper phosphate glasses showed that as the divalent ionic radius increases, the room temperature conductivities decrease in the order MgO>ZnO>CaO. CuO in copper metaphosphate glass results in an increase in the electrical conductivity, replacing alkali metal oxide for 20 mol.%.

A series of barium titanium oxide with various Ba/Ti ratios having a hollandite structure was obtained by ceramic technique. It was shown that barium titanium hollandites may adopt both oxygen excess and oxygen deficient stoichiometries within the structure. As a limiting case the barium titanium hollandites with only tetravalent titanium ions were obtained. Results of investigation samples in the general formula BaxTi4-2xFe2xO8; 0.1 ≤ x ≤ 1 were measured at different temperatures from room temperature up to 800 K as a function of frequency ranging from 400 kHz to 5 MHz. The dielectric constant (ε′) indicated that the increase of its value with increasing temperature is due to presence of more than one type of polarization act in cooperation with each other. The values of activation energy were calculated from the resistivity data. The calculated values of activation energy at low temperature (ferrimagnetic region E1) are less than those in the high temperature (paramagnetic region E11) which are frequency independent part. This is because in the monoclinic hollandite under investigation has Ba ions which occupy the center of the tunnel surrounded by TiO2 and Fe2O3 octahedral in spite of the large size of Ba2+ ions (1.35 Å). Peak in the dielectric loss tangent versus frequency curves are observed in some concentration and the possible mechanisms are discussed. © 2005 Elsevier B.V. All rights reserved.

A series of barium titanium oxide with various Ba/Ti ratios having a hollandite structure was obtained by ceramic technique. It was shown that barium titanium hollandites may adopt both oxygen excess and oxygen deficient stoichiometries within the structure. As a limiting case the barium titanium hollandites with only tetravalent titanium ions were obtained. Results of investigation samples in the general formula BaxTi4-2xFe2xO8; 0.1 ≤ x ≤ 1 were measured at different temperatures from room temperature up to 800 K as a function of frequency ranging from 400 kHz to 5 MHz. The dielectric constant (ε′) indicated that the increase of its value with increasing temperature is due to presence of more than one type of polarization act in cooperation with each other. The values of activation energy were calculated from the resistivity data. The calculated values of activation energy at low temperature (ferrimagnetic region E1) are less than those in the high temperature (paramagnetic region E11) which are frequency independent part. This is because in the monoclinic hollandite under investigation has Ba ions which occupy the center of the tunnel surrounded by TiO2 and Fe2O3 octahedral in spite of the large size of Ba2+ ions (1.35 Å). Peak in the dielectric loss tangent versus frequency curves are observed in some concentration and the possible mechanisms are discussed. © 2005 Elsevier B.V. All rights reserved.

A series of barium titanium oxide with various Ba/Ti ratios having a hollandite structure was obtained by ceramic technique. It was shown that barium titanium hollandites may adopt both oxygen excess and oxygen deficient stoichiometries within the structure. As a limiting case the barium titanium hollandites with only tetravalent titanium ions were obtained. Results of investigation samples in the general formula BaxTi4-2xFe2xO8; 0.1 ≤ x ≤ 1 were measured at different temperatures from room temperature up to 800 K as a function of frequency ranging from 400 kHz to 5 MHz. The dielectric constant (ε′) indicated that the increase of its value with increasing temperature is due to presence of more than one type of polarization act in cooperation with each other. The values of activation energy were calculated from the resistivity data. The calculated values of activation energy at low temperature (ferrimagnetic region E1) are less than those in the high temperature (paramagnetic region E11) which are frequency independent part. This is because in the monoclinic hollandite under investigation has Ba ions which occupy the center of the tunnel surrounded by TiO2 and Fe2O3 octahedral in spite of the large size of Ba2+ ions (1.35 Å). Peak in the dielectric loss tangent versus frequency curves are observed in some concentration and the possible mechanisms are discussed. © 2005 Elsevier B.V. All rights reserved.

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