Studies Of Physical-chemical Properties Of
STUDIES OF PHYSICAL-CHEMICAL PROPERTIES OF
THE HIGH-TEMPERATURE SUPERCONDUCTORS IN VACUUM
AND CONTROLLED ENVIRONMENTS
G.W. Chadzynski
Telecommunications Research Institute, Wroclaw Division,
Grabiszynska st. 97, 53-439 Wroclaw, Poland and
Wroclaw University of Technology,
Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland
Many physical-chemical properties of oxide superconductors [1] depend on oxygen content and its distribution in the sample. It is known that atmospheric contaminants such as CO2 and H2O can have strong effects on superconducting transition temperature, the critical current density and the width of the superconducting transition of the superconductors [2]. For practical applications of the high – Tc superconductors, it is necessary to make long, continuous superconductors in a variety of shapes. Knowledge of the chemistry and thermodynamics of the superconducting oxides is essential not only for prediction of the optimum processing conditions for the different forms of the materials, but also for an understanding of the origins of the defects. Investigations of the thermal decomposition of the oxide superconductors in dynamic vacuum are valuable, particularly in view of the high oxygen diffusion coefficient in these cuprates [3]. Dynamic vacuum protects against the readsorption of oxygen from the environment.
Hydrogen has an extremly simple electronic structure and a small mass but is capable of causing substantial perturbations of local electron density with a comparatively slight distortion of the lattice [3].
Investigations of the influence of the oxygen isotope substitution on the properties of the high-Tc oxide superconductors [4] is very important understanding the mechanism of superconductivity. The observation of an oxygen isotope effect provides supporting evidence that phonons play a role in the electron pairing mechanism [5].
Samples of the high-temperature superconductors were synthesised from stoichiometric mixtures of high-purity oxides and carbonates. The ground
powders were homogenised manually or by a mechanical ball mill and subsequently sintered in oxygen for 12 h at 9500 C with several intermediate grindings. The final samples were oxygen-quenched from 950° C to room temperature and found to be single phase by powder X-ray diffraction. The lattice parameters of all preparations were controlled, in both initial and final experiments using a Stadi P (Stoe) diffractometer with a position-sensitive detector (Cu Ka radiation). The oxygen content was measured by iodometric titration width a reproducibility of at teast 0.02.
DC four probe resistivity measurements were performed on pellets to which copper contacts were attached by using silver paint.
Termogravimetric analyses (TG) were performed by using a Cahn RG ultramicrobalance system [6], with heating in vacuum and controlled environments at a rate of 5° C min-1 in order to study mass uptake or loss at higher temperature.
The purpose of the present paper is to show the application of different methods to study of high-temperature superconductors.
References
1. H. Shaked, P.M. Keane, J.C. Rodriguez, F.F. Owen, R.L. Hitterman and J.D. Jorgensen (Eds.), Crystal Structurs of the High-Tc Superconducting Copper-Oxides, Elsevier, Amsterdam 1994.
2. P. Staszczuk, G.W. Chądzyński and D. Sternik, J. Therm. Anal. Cal., 62 (2000) 451.
3. G.W. Chądzyński, J. Therm. Anal. Cal., 62 (2000) 353.
4. K. Conder, E. Kaldis, M. Maciejewski, K.A. Muller and E.F. Steigmeier, Physica C, 210 (1993) 282.
5. K.A. Muller, Z. Phys. B, Cond. Matt., 80 (1990) 193.
6. G.W. Chądzyński, J.Therm. Anal. Cal., 55 (1999) 661.
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