627 RoPM 2000 Cluj-Napoca, Romania Second International Conference on Powder Metallurgy, 6-8 July 2000 HIGH-Tc SUPERCONDUCTING MATERIALS. COMPARATIVE STUDY: COPRECIPITATION VS SOLID STATE PHASE PREPARATION L. Marta*, I. Gr. Deac**, V. Fruth***, M. Zaharescu***, L. Jäntschi* *Technical University of Cluj-Napoca, Romania, **"Babeş-Bolyai" University of Cluj-Napoca, Romania, ***Institute of Physical Chemistry, Romanian Academy of Sciences, Bucharest, Romania ABSTRACT: The Bismuth - based compounds (BSCCO type) were prepared by two methods: The conventional method of solid state reaction and a chemical method (oxalate coprecipitation). Superconductor phases obtained by thermal decomposition of the precursors are identified from X-ray diffraction. The electric and magnetic properties of the new compounds are investigated. The results are compared in order to evaluate the potential of preparation methods. KEYWORDS: BSCCO system, coprecipitation, X-ray dimaction, superconductivity 1 INTRODUCTION Superconductors are generally obtained by conventional solid state reaction between oxides or carbonates. Wet chemical methods have been extensively used in the last years for preparation of high temperature bismuth based ceramic superconductors, in order to increase the reactivity of precursor powders. The main chemical methods include coprecipitation (oxalates, carbonates, citrates, e.a.), complex formation and sol-gel techniques [1 -11]. In the present paper, the oxalate precursors for the BSCCO system was synthesized in the previously established conditions, at the different pH values. These powder precursors were characterized by DTA and X-ray powder diffraction analysis. The electrical and magnetic measurements were performed for the samples prepared at different pH values and for the samples thermal treated at different temperature, with the aim to establish the instruments of preparing conditions of the samples on the structure, phase formation and electrical and magnetic properties. 2 EXPERIMENTAL The oxalate precursors were prepared by coprecipitation, using a previously mentioned method, [12, 13], from nitrate solutions of bismuth (III), strontium (II), calcium (II) and cooper (II) with an excess of oxalic acid (0.1M) followed by addition of NaOH (0.1M) in order to adjust pH at the desired values. Three samples are prepared at the pH values of 2.5 and 4. For the comparison, the solid state samples ware prepared by wet mixing of the solid state compounds: Bi 2 O 3 , CuO, CaCO 3 and SrCO 3 (reagent grade) for 1h. The samples as obtained were characterized by the Differential Thermal Analysis and X-ray powder diffraction. The thermal treatment schedule was established on the basis of the DTA data: The X- ray diffraction patterns were recorded at the different temperature of thermal treatment as follows: 750, 800 and 850 °C, as well as the electrical and magnetic properties. The electrical resistance and the a.c. susceptibility as a function of temperature were carried out.