Victor Fruth

Phases investigation in the antimony doped Bi2O3 system

The present study investigates the influence of Sb ions, introduced as dopants in α-Bi 2 O 3 , on the structure of the oxide polymorph forms obtained at high temperature. The structural changes of α-Bi 2 O 3 for compositions in the system Bi 2-x Sb x O 3 (x=0, 0.05, 0,1, 0.15, 0.2), at different thermal treatment temperatures were analyzed by thermal analysis, powder X-ray diffraction and infrared transmission spectroscopy. A tendency of the structure to change to a higher symmetry (monoclinic → tetragonal → cubic) was observed, as the content in antimony increased and the temperature reached 850 °C. The presence of Sb 2 O 3 in the Bi 2 O 3 oxide system promotes an oxygen release from the oxide and enlarges the stabilization domain of the δ-phase.

High-Tc phase obtained in the Pb/Sb doped Bi-Sr-Ca-Cu-O system

Abstract Partial replacement of Bi by Pb and Sb produces materials of high- T c pure phase, with antimony playing an important role in accelerating the formation of the phase with the higher superconductive transition in the Bi–Sr–Ca–Cu–O system. The influence of the antimony precursors on the superconducting phases mechanism formation was examined. Using a solid state reaction route, two nominal compositions Bi 1.6 Pb 0.3 Sb 0.1 Sr 2 Ca 2 Cu 3 Oy and Bi 1.6 Pb 0.4 Sb 0.1 Sr 2 Ca 2 Cu 4 Oy were investigated. The sources of antimony were Sb 2 O 3 , α Sb 2 O 4 and a prepared mixture Bi 1.9 Sb 0.1 O x . The mechanism formation of the phases upon annealing was investigated using X-ray diffraction and simultaneous thermal analysis. Electrical properties of the obtained materials were evaluated. The presence of the antimony ions determined a higher reactivity of the system as well as the promotion of the superconducting high- T c phase enhancement.

Lanthanum chromites doped with divalent transition metals

Abstract Heteropolynuclear complex compounds isolated in Cr 2 O 3 · x H 2 O–La(NO 3 ) 3 –M(NO 3 ) 2 –A–NH 3 , (A=CH 3 COO − ,C 2 O 4 2− ; M=Cu, Ni) systems were used as precursors for LaCr 1− x M x O 3 . The perovskite structure of doped lanthanum chromites was determined by XRD analysis. The unit cell volumes, specific surface areas and magnetic properties were investigated. The proposed methods offer new, simple, less expensive procedures for obtaining doped lanthanum chromites.

Promotion of high-Tc phase in B-doped (Bi, Pb)2Sr2Ca2Cu3Oy superconductors prepared by the melt-quenching method

Abstract We prepared superconducting Bi1.6Pb0.4−xBxSr2Ca2Cu3Oy (x=0, 0.1, 0.2, 0.3 and 0.4) ceramics by the melt-quenching method and examined the effect of B addition on the formation of the high-Tc phase.The temperatures and sequence of formation of the superconducting phases within this composition were determined using simultaneous differential thermal analysis (DTA) and thermogravimetric analysis (TGA), X-ray powder diffraction (XRD). It was found that the bulk ceramics with x=0.1 and 0.2 exhibited superconductivity with a critical temperature range of 95–100 K. The lowering of the partial melting temperature caused by the coexistence of Pb and B elements is effective for the formation mechanism of the high-Tc phase.

Antimony Doped Bi2O3 Thin Films

Bismuth oxide system exhibit high oxide ionic conductivity and have been proposed as good electrolyte materials for application such as solid oxide fuel cell (SOFC) and oxygen sensor. A preliminary investigation for depositing thin and dense antimony doped Bi2O3 films based on wet chemical routes was realized. Antimony doped Bi2O3 films were deposited onto glass substrate from bismuth nitrate and antimony precursor solutions. As chelating agent polyethyleneglycol (PEG) was used and the above-mentioned precursor solutions were sufficiently viscous. Crystallization behavior and microstructure evolutions of the obtained films were investigated using spectroscopic ellipsometry (SE), polarized microscope observation, X-ray diffractometry (XRD), and infrared spectrometry (IR). The thickness and the porosity of the films were evaluated. The preparation techniques differ mainly in precursor materials and method of deposition, leading to different quality of the resulting films.

Influence of the powder characteristics on the properties of the Bi-based superconductors

Abstract Bi-based ceramic materials with superconducting properties were prepared using the solid state reaction technique, starting with reactive powders obtained via oxalate coprecipitation, as well as by the traditional powders route. The powder characteristics were evaluated using BET method and transmission electron microscopy (TEM). The stages of the high T c supeconducting phases formation process were investigated by TG, DTA, XRD and IR methods. The dependence of the electric resistance versus temperature was recorded. The densities of the obtained samples have been also determined. The results emphasised high reactivity and shorter reaction times of the ceramic bodies obtained by the coprecipitation method.

Influence of Hydrothermal Method on the Aluminum Titanate Synthesis

Eutectoid decomposition and mechanical properties limit the well-known properties of aluminum titanate desired in several applications. In order to minimize these limitations new synthesis routes and additives were studied. In the present work, aluminum titanate precursor powders were prepared by hydrothermal method, starting with metal alkoxide reagents. The influence of Al and Ti sources and the experimental conditions were investigated by XRD, IR spectroscopy, DTA/TG and TEM methods. The aluminum titanate precursor powders obtained by hydrothermal method presented good homogeneity and very small grain size. XRD and evaluation of ceramic properties established the evolution of phase composition during sintering in the 12501400oC ranges.