The suppression of superconductivity is studied in the system of Pr0.5R0.5Ba2Cu3O7-y (R=rare-earthelement). X-ray structural investigation reveals the different changes of cell volume with increasing ion radius in these compounds in comparison to X0.5R0.5Ba2Cu3O7-y (X=Ho, Sm). Results are discussed in terms of Pr-O hybridization. It is suggested that there exists a critical average ion radius above which superconductivity in the RPr systems does not persist.

Experimental results showing the temperature dependence of the conductivity of a variety of Pr-RE-Ba-Cu-O (RE = Er, Yb, Lu, and Tm) compounds are presented. The semiconducting behavior of the conductivity observed is analysed using ln sigma approximately T-2/5 and ln sigma approximately T-1/4 laws suggested, using the small-polaron hopping model by Triberis et al., for the high- and low-temperature regime, respectively. The agreement of the experimental data with these models is very satisfactory, giving a meaningful interpretation of the transport mechanism of these materials.

A new method for the determination of melt equilibria has been developed to clear some aspects of the phase relationships in the Y-Ba-Cu-(O) system at 950°C in air and at 975°C in oxygen. The procedure is based on the separation of the melt from an equilibrium sample and the consequent analysis of its solid residue. Approximative liquidus curves were suggested and boundaries of four primary crystallization fields were estimated.

There are two contributions which influence the resulting oxygen stoichiometry of the superconducting materials, the mean valence of copper ions and the concentration of the peroxide anions. To separate the two contributions a procedure based on the determination of the total oxygen stoichiometry employing the Fe2+/Fe3+ system and the polarographic determination of the perixidic oxygen was developed. The procedure was tested on YBa2Cu3O7−x samples prepared at various conditions.

The Y∶Ba∶Cu=1∶2∶3 coprecipitates of carbonates (precipitated with Na2CO3 or Na2CO3-NaOH solution) and of oxalates (obtained in aqueous, partly aqueous and non-aqueous media) were investigated as concerns the yield and stoichiometry of the precipitates, including their transmission electron microscopy and DTA characteristics. Oxalates coprecipitated from acetate solutions in non-aqueous media provide fine samples with increased reactivity. For comparison, when thermally treated, an oxide ceramic mixture containing aged BaO (with some Ba(OH)2 and BaO2) exhibits increased reactivity due to the formation of a liquid phase in the temperature range 400–500°.

Thermal treatment of the original superconducting phase YBa2Cu3O7−x in the temperature range of 300–800°C showed a mutual effect of the oxygen stoichiometry, ordering of the oxygen vacancies and microstructure. Two superconducting phases having TC ≈ 90 K and TC ≈ 50 K, separated by two-phase coexistence region were found in the samples a quenched down from the respective temperatures.

Crystal Research and TechnologyVolume 23, Issue 1 p. K6-K10 Short Note Effect of the pressing on the properties of the superconducting YBa2Cu3O7—γ Phase E. Pollert, E. Pollert Institute of Physics, Czechoslovak Academy of Sciences, Na Slovance 2, 18040 Prague 8 — Libeň, CzechoslovakiaSearch for more papers by this authorJ. Hejtmánek, J. Hejtmánek Institute of Physics, Czechoslovak Academy of Sciences, Na Slovance 2, 18040 Prague 8 — Libeň, CzechoslovakiaSearch for more papers by this authorK. Jurek, K. Jurek Institute of Physics, Czechoslovak Academy of Sciences, Na Slovance 2, 18040 Prague 8 — Libeň, CzechoslovakiaSearch for more papers by this authorJ. Kamarád, J. Kamarád Institute of Physics, Czechoslovak Academy of Sciences, Na Slovance 2, 18040 Prague 8 — Libeň, CzechoslovakiaSearch for more papers by this authorA. Tříska, A. Tříska Institute of Physics, Czechoslovak Academy of Sciences, Na Slovance 2, 18040 Prague 8 — Libeň, CzechoslovakiaSearch for more papers by this authorD. Zemanová, D. Zemanová Institute of Physics, Czechoslovak Academy of Sciences, Na Slovance 2, 18040 Prague 8 — Libeň, CzechoslovakiaSearch for more papers by this author E. Pollert, E. Pollert Institute of Physics, Czechoslovak Academy of Sciences, Na Slovance 2, 18040 Prague 8 — Libeň, CzechoslovakiaSearch for more papers by this authorJ. Hejtmánek, J. Hejtmánek Institute of Physics, Czechoslovak Academy of Sciences, Na Slovance 2, 18040 Prague 8 — Libeň, CzechoslovakiaSearch for more papers by this authorK. Jurek, K. Jurek Institute of Physics, Czechoslovak Academy of Sciences, Na Slovance 2, 18040 Prague 8 — Libeň, CzechoslovakiaSearch for more papers by this authorJ. Kamarád, J. Kamarád Institute of Physics, Czechoslovak Academy of Sciences, Na Slovance 2, 18040 Prague 8 — Libeň, CzechoslovakiaSearch for more papers by this authorA. Tříska, A. Tříska Institute of Physics, Czechoslovak Academy of Sciences, Na Slovance 2, 18040 Prague 8 — Libeň, CzechoslovakiaSearch for more papers by this authorD. Zemanová, D. Zemanová Institute of Physics, Czechoslovak Academy of Sciences, Na Slovance 2, 18040 Prague 8 — Libeň, CzechoslovakiaSearch for more papers by this author First published: January 1988 https://doi.org/10.1002/crat.2170230121Citations: 6AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume23, Issue1January 1988Pages K6-K10 RelatedInformation

The simultaneous effect of the oxygen stoichiometry, ordering of oxygen anions and the microstructure on the superconducting properties of YBa2Cu3O7−χ was investigated on the samples annealed at suitable temperatures and subsequently quenched and/ or slowly cooled down to room temperature. It was found that the variation of the oxygen stoichiometry influences above all the stability of the orthorhombic phase and the elementary cell volume while the ordering of oxygen vacancies contribute to the formation of the “90 K” and “60 K” orthorhombic superconducting phases.

By choosing suitable PbO-B2O3-Bi2O4 melts combined with appropriategrowth conditions it is possible to reduce significantly the content of lead atoms in garnet films leading to the incorporation of approx. 0·1 Pb per one Bi atom (y/x≈ ≈ 0·1).