F~i~ Solid State Communications, Vol.66,No.9, pp.961-963, 1988. ~,,~,~_ Printed in Great Britain. 0038-1098/88 $3.00 + .00 Pergamon Press plc SUPERCONDUCTIVITY IN SULPI1UR DOPED Y-Ba--Cu-O SYSTEM D. Bhattacharya, S.K. Ghatak, T.K. Dey, P. Pramanik and K.L. Chopra, Indian Institute of Technology, Kharagpur - 721 30Z, India and M. Bhatnagar and D.K. Pandya Indian Institute of Technology, New Delhi - 110 0160 India (Received 25 February 1988 by C.N.R. Rao) Sulphur substituted YBazCu3SO6_ x superconducting powder was prepared by the ceramic route. The material, in bulk, showed zero resistivity at 88 K and the onset of diamagnetism at 90 K. Magnetisation behaviour confirms type II behaviour of the superconducting state. The ESCA and IR spectrum on the superconducting compound at room temperature, indicate the location of the sulphur at the apex of the octahedral coordination sphere of the Cu(Z)-ion in the crystal lattice. The discovery of superconductivity in Y-Ba-Cu- O system above 77 K [1] has led to an all out effort to improve upon the properties of these high temperature superconductors. In an effort to increase T c various substitutions at the cationic and anionic sites have been attempted. The substitution of Y by other trivalent rare earths have lille effect on changing T c [Z]; however large reduction of T c have been reported with lanthanides which have multivalent states [3]. Partial fluorination of YBazCu307_ x compound have been claimed to cause a rise of T c to higher temperatures [4,5] but the role of fluorine is not clearly understood. On the other hand T c drops rapidly if Cu is substituted by other transition series elements and it also depends on oxygen content [6]. This clearly demonstrates the unique role of Cu and O for the superconducting state. It is argued that the electrons in quasi-two dimemsional layer of Cu - O in these compounds are responsible for the superconductivity and that the hybridisation between the Cu-3d states and O-Zp state is an important element in pairing. As the covalency increases from O to S, the substitution of O by S is expected to lead to higher hybridisation effct which could change superconducting properties of the compounds. Therefore it is pertinent to investigate the effect of sulphur substitution on the superconducting state of Y-Ba- Cu-O compound. In this communication we report on the bulk superconductivity in YBazCu3SO6_ x and the possible position where the sulphur substitut'es oxygen. Stoichiometric amounts of YzO3, BaCO 3 and CuO (all 99.99% pure) were ball milled in a mechanical agate using isopropyl alcohol as the suspending medium. The ball milled mass was dried at 150 C and then calcined at 950°C for 24 hours in a platinum crucible in air. The calcined mass was then cooled to room temperature and ground to 0.5 pm powders in a mechanical agate. The powder was pelletized with PVA as binder to improve the green strength. The pellets were sintered at 950°C under constant oxygen flow for 10 hours and were then cooled very slowly to room temperature under constant oxygen flow. X-ray diffraction of this compound shows that the orthorhombic structure as seen in superconducting YBa2Cu307_ x is maintained in YBazCu3SO6_ x. The analysis of diffraction pattern does not show the presence of free S, BaS, CuS or YzS3. Energy dispersive X ray analysis of the surface of the pellets confirm presence of Y, Ba, Cu and S. The presence of S in the sintered pellets have also been verified by Auger electron spectroscopy (Fig. 1). ;l'he scanning electron micrograph of the superconducting sample of YBazCu3SO6_ x show extensive grain growth (Fig. Z) but no columnar growth as seen in YBazCu307_ x is observed for the sulphur substitiuted compound sintered at 950 ° C. Four probe resistivity measurement was carried out on samples with dimensions 1Z x Z x Z ram; the specimen was slowly cooled to 77 K in a cryostat filled with helium gas at Z0 mm of Hg pressure. The resistivity measurement was carried out during the heating cycle from 77 K to 300 K. The sample was metallic in nature and the resistivity varied linearly with temperature from 300 K to the temperature of onset of superconductivity. The zero resistence state was reached at 88 K (Fig. 3). Magnetic measurements were carried out by fluxmetric method with integrating flux meter (Walker Scientific model MF-3} in samples with dimensions. 10 x 3 x Z mm. The magnetisation was measured in two different ways: (i) the sample was field cooled from above T c and the Meissner branch was measured 0 I I I I BQ I I I l I I00 ZOO 300 400 500 600 700 I00 tl00 14)00 KINETIC ENERGY, eV Fig. 1-AES spectrum of YBa2Cu3SO6_ x pellet sintered at 950°C under oxygen. 961