A. A. Bahgat

Physical properties of some rare earth tellurite glasses

Mossbauer and IR spectra as well as the electrical conductivity have been measured to give an idea about the structure and the electrical properties of some rare earth tellurite glasses containing Fe2O3. The glasses denoted [1 − (2x + 0.05)] TeO2 ·xFe2O3 · (x + 0.05) Ln2O3, wherex = 0.0 and 0.05 and Ln = lanthanum, neodymium, samarium, europium or gadolinium, were prepared by fusing a mixture of their respective reagent grade oxides in a platinum crucible at 800° C for one hour. The Mossbauer parameters such as isomer shift, quadruple splitting and line width were found to be a function of the polarizing power (charge/radius) of the rare earth cations. The Mossbauer parameters were not affected by the heat treatment of the glass samples. Both of the Te-O-Ln and Te-O-Fe stretching vibrations were obtained from the IR results which indicate that the rare earth oxides and iron oxide are partially covalent. The electrical resistivity was measured as a function of temperature from 293 to 520 K. Both the electrical resistivity and the activation energy were found to be a function of the atomic number (Z) of the rare earth cations. The results were interpreted on the basis of the electronic structure of the glass.

Mixed valent iron in Biotite

Biotites from the Eastern desert of Egypt are the subject of the present study. Mössbauer effect, X-ray diffraction and Chemical analysis were done. A strong electronic exchange interaction state was observed between neighbouring M1 and M2 positions. Correlations between the results obtained from different techniques are given on the basis of the electronic and structure characteristics of Biotite.

The influence of substitution of iron ions on the electron hopping in magnetite

Two commercial spinel ferrites, (Fe0.192+Mg0.562+Mn0.252+) (Fe1.873+Al0.133+)O42- and (Fe0.552+Mg0.322+Mn0.032+Cu0.102+) (Fe1.73+Al0.263+)O42-, were investigated with a view to obtaining more information about the influence of varying the proportion of Fe2+ ions on its Mossbauer effect spectra. For the first composition, for which there is a sufficient number of substituted cations for them to be located at the six nearest neighbours to Fe2+ ions, no transition between Fe2+ and Fe3+ ions occurred. On the other hand the observed broadening of the octahedral ferric spectrum for the second compound gave evidence for the electron relaxation of neighbouring Fe2+ and Fe3+ ions; this spectrum also contained a third sextet with a stronger sharp Fe2+ character. Thus it has been established that the fast electron hopping process present in this case is essentially a pair localised phenomenon. The Mossbauer effect parameters were calculated for these observed sites, and their variation with temperature discussed.

Glass formation of the binary TeO2 · NiO system

On etudie des systemes de composition xNiO•(1−x)TeO 2 avec x compris entre 0,05 et 0,35. On suit la zone de formation du verre ainsi que sa structure par spectrometrie IR

Study of the effect of Na/Cu substitution in Bi4Sr3Ca3Cu4O16 glass-ceramic superconductor

The composition Bi4Sr3Ca3Cu4−xNaxO16 for x=0.2, 0.4, 0.6, 0.8 and 1.0 was examined, in order to study the effect of Na/Cu substitution on both the glass-forming ability as well as the superconducting properties of the glass-ceramic (GC) phase. Because the GC phase of the composition Bi4Sr3Ca3Cu4O16 (4334) showed superconducting properties below 78.5 K, the crystalline phases formed after heat treatment were identified by X-ray diffraction. This suggests that Na+ substituted the Cu+ cations. The GC phases were studied by X-ray diffraction, differential thermal analysis, infrared absorption, d.c. electrical conductivity and low-temperature a.c. magnetic susceptibility in the temperature range 77–300 K. The present results support the considerations that the addition of sodium enhances the crystallization of the 4334 phase while sacrificing the glass-forming ability. The crystalline phases precipitated from the rapidly quenched glasses in the Bi-Sr-Ca-Cu-Na-O system were greatly dependent on the heat-treatment time as well as the treatment temperature. The stability and crystallization process of the glass differ greatly depending on the sodium content which acted as fluxing agent. Considering that the formation of the 4334 phase is largely enhanced in sodium-doped samples, it is concluded that the lowering of the partial melting temperature is very important for the enhancement of the formation of the 4334 phase, as well as in raising the critical transition temperature. Infrared spectroscopy measurements indicate that part of the ceramic phase is non-metallic. The two-probe method and the standard four-point probe method electrical resistivity indicate that Bi-Sr-Ca-Cu-Na-O superconductor formation was greatly dependent on heat-treatment time as well as treatment temperature. The superconducting crystalline phase, which grew upon heat treatment, was identified as a quasi-tetragonal phase 4334. Electrical resistance measurements together with thermopower results indicate that the electrical properties move from a metal region to a semiconducting region according to the magnetic phase diagram of oxide superconductors. Superconducting 4334 phase with Tc=84 K could be successfully prepared by the GC techniques within 1–2 h thermal cycling, which renders a great saving in processing costs and is a simple method of moulding superconducting articles.

Gabbro-Metagabbro association: a Mössbauer effect study

Six different samples of Gabbro-Metagabbro rocks from Gebel (Mountain) Atud area located in the central Eastern Desert of Egypt were collected and studied using Mössbauer effect of iron and x-ray diffraction. The study pointed out the degree of alteration from the point of view of mineralogical identification together with the amount and different of states of iron. A mixed valence iron state was observed in one sample.

On the magnetic behaviour of cadmium nickel ferrites

The magnetic behaviour of the mixed ferrite CdxNi1−xFe2O4 system withx ranging from 0 to 0.9 are studied at different temperatures using the Mössbauer technique. The one-third power law and the empirical relation of the hyperfine magnetic fields (A-B) site dependence are verified. Néel points are determined for all compounds and the magnetic interactions are also discussed.

Analysis of the corrosion products of an Fe81B13.5Si3.5C2 amorphous alloy

Abstract The corrosion tendency and the products of the amorphous alloy Fe 81 B 13.5 Si 3.5 C 2 in KCl solution were analysed using the mass loss, X-ray diffraction and Mossbauer effect techniques. It was observed that the amorphous alloy is more active in KCl solution than metallic iron is. There is no evidence that the final products obtained from the alloy in its amorphous state, from the alloy in its crystalline state and from metallic iron are different in nature and composition. The final products of iron are oxyhydroxides with different phases which have a particle size of less than 17 nm.

Investigation of the high-temperature superconductor Tl−Ca−Ba−Cu−Fe−O in a wide range of temperature and iron concentration

A series of the composition Tl2Ca2Ba2Cu3−xFexOδ with 0≦x≦0.1 were prepared by the usual ceramic method. The superconducting behaviour was investigated by electrical conductivity and Mössbauer effect. X-ray diffraction on the samples was also used to study the different phases. The study revealed a superconducting transition temperature about 100 K for samples withx=0.00 and above 80 K forx=0.02 and 0.04. From the Mössbauer effect spectra measured for different compositions and at different temperatures, it is evident that the Fe ions substituted Cu into different sites. A clear evidence of vibration anisotropy is observed, together with a low spin state for each position. These results are discussed on the basis of the structure and electronic state of the compounds.

Iron Site Population in Garnets from the Arabo-Nubian Shield

Recently it has been found in two different locations in South Eastern Desert of Egypt that some pegmatitic veins which invaded in gneissic rocks are associated with Yttrium bearing garnets with the general chemical composition c3a2d3O12. The concentration of Yttrium in these garnets reached 10,000 ppm. Garnets with lower concentration up to 300 ppm were also found in south Sinai peninsula, and are associated with metamorphosed sedimentary rocks. Both locations are part of the Arabo-Nubian Shield, and were mapped using Landsat images (TM) and extensive field work. In the present study our main concern was to determine the cation site population and chemical composition of all samples. Two different garnets structure models were identified. The typical occurrence of spessartine, almandine and pyrope were present and confirm the site population.