ELSEVIER Physica C 341-348 (2000) 2459-2460 www.elsevier.nl/Iocate/physc Synthesis of (Hg,Re-1223) by Sol-Gel technique A.Sin a, P.Odier a, F.Weissb, M.Nfifiez-Regueiroc aLaboratoire de Cristallographie-CNRS, 25 Av. Des Martyrs, Bp166, F38042 Grenoble CEDEX09, France bLaboratoire des Mat6riaux et du G6nie Physique - ENSPG-INPG-CNRS UMR5628, F-38402 St Martin d'H6res Cedex, France CCentre de Recherche sur les Tr6s Basses Temp6ratures-CNRS, 25 Av. des Martyrs, Bp166, F38042 Grenoble Cedex09, France In this work we prepare (Hg,Re)-1223 superconducting samples using the acrylamide gelification for obtaining nanoparticles of precursor phase of mercury-cuprates such as "Reo.25BazCa2Cu30×". This chemical method is fast, cheap, reproducible and easy to scale up. Also, we demonstrate that sol-gel processing is a more efficient than solid state reaction for obtaining the superconductor phase. Finally, diagram of Pressure of synthesis versus. 1/T are shown and discussed. 1.-INTRODUCTION The mercury-cuprates are generally synthesised by the sealed quartz tube technique in a two step process: the formation of a precursor first and then its mercuration. Starting with a high degree of homogenisation of all precursor oxides is essential to obtain superconducting ceramics of high quality. Wet chemistry, and particularly sol- gel processing is one of the most promising way to get an excellent homogenisation at an atomic scale of the elements and a high reactivity of the precursors. We have studied a sol-gel method for processing the precursors "RexBa2Ca2Cu3Ox". We use the gelification of a solution by an in-situ polymerisation of acrylamide monomers. This method is much more rapid and safe than the so- called nitrate-citric route that involves nitrates, citrates and also ethylene glycol. In-situ pressure measurements (TBA) [1,2]] were carried out to monitor the mercuration synthesis of the precursors in closed tubes. 2.-EXPERIMENTAL The synthesis of fine powders of complex oxides are carried out by dissolving separately each cations in their stoichiometric ratio (CaCO3 (DIOPMA 99.95%),), BaCO3 (DIOPMA 99.9%), CuO (99.99% DIOPMA) and Re (99.9% Aldrich) in nitric acid. The Cu 2+ and Re 6+ cations are complexed with addition of acid-EDTA: (H4Y)=[CHzN(CH2COOH)2]2 (Prolabo 98%) in the ratio 1:1 and the pH is adjusted to be in a range of pH where the solution is perfectly clear (pH=3). Finally they are mixed all together.. To this solution (150ml) are added (10g/lg) Acrylamide monomers (Aldrich 99 %) and N,N'- Methylenebisacrylamide (Aldrich 99%). A few mg of a chemical initiator c~ ct'-Azo- isobutyronitrile=AIBN (Fluka 98 %) is added to initiate the polymerization. With AIBN the polymerization is fast at 80°C. The gel is then dried a few minutes in a microwave oven. It results from this treatment an extremely porous foam material. The xerogels obtained are then homogenized in a ceramic mortar and one subsequent thermal treatment, optimized to each particular composition is sufficient to get the pure phase. Its temperature is a higher than 700 °C, a temperature necessary to remove most of the organic phase (>90 %). In our case it we used 850°C for 10h in a rich N2 flux flow. This precursor is then mixed with HgO (99%, Aldrich) 0921-4534/00/$ - see front matter © 2000 ElsevierScience B,V. All rights reserved. PII S0921-4534(00)01181-3