E. E. Shaisha

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.

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.

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.

Preparation and characterization of the high-temperature superconductor YBa2Cu3O7–x

Mesures de conductivite electrique, analyse radiocristallographique et analyse par thermogravimetrie du compose Y-Ba-Cu-O qui peut etre supraconducteur haute temperature ou semiconducteur selon la preparation

Mössbauer and infra-red spectra of some alkaline earth phosphate and borate glasses

Abstract Mossbauer and infra-red spectra were measured for a series of alkaline earth phosphate and borate glasses with mole% composition (100 - x ) P 2 O 5 + x Me O + 5 SnO 2 (where Me = Mg, Ca, Sr or Ba and x = 20, 24, 28 or 32). The results were analyzed as a function of glass composition and tin atoms valence state. The decrease in the isomer shift (IS) value with the increase of the alkaline earth oxide content was attributed to an increase in the ionic strength of bonds around the tin ions. The increase of the quadrupole splitting (QS) and the line width (LW) values with the gradual increase of alkaline earth oxide content were attributed to be due to an asymmetric and irregular distribution of alkaline earth ions around the tin ions. There is non-significant variation between these parameters when results for phosphate and borate glasses are compared. The asymmetry in the absorption peak is due to Goldanskii effect. The tin was found only in the quadrivalent state. The effect of tin on the infra-red absorption peaks was also studied and the different phosphorous groups were determined.