Solid State Communications, Vol. 79, No. 7, pp. 615-619, 1991. Printed in Great Britain. 0038-1098/91 $3.00 + .00 Pergamon Press plc SULPHUR SUBSTITUTION FOR OXYGEN IN YBa2Cu307 CERAMICS R. Cloots and A. Rulmont S.U.P.R.A.S., Institut de Chimie, B6, Universit6 de Li6ge, B-4000 Li6ge, Belgium P.A. Godelaine, C. Hannay and H.W. Vanderschueren S.U.P.R.A.S., Institut d'Electricit6 Mont6fiore, B28, Universit6 de Li6ge, B-4000 Li6ge, Belgium and M. Ausloos S.U.P.R.A.S., Institut de Physique, B5, Universit6 de Li6ge, B-4000 Li6ge, Belgium (Received 8 March 1991 by D. Van Dyck) We have studied the effect of sulphur addition on the structural proper- ties of YBa2Cu307 ceramics. We have developed a new synthesis method in order to prepare YBa2CuaO6+xSy without any impurity phases. We have analyzed the superconducting properties and we report a different susceptibility behaviour for the sulphur doped com- pound that it can be easily correlated to oxygen concentration. The microstructure is also examined from the point of view of compactness effect on the susceptibility behaviour. 1. INTRODUCTION SINCE the discovery of high-temperature super- conductivity in the YBa2 Cu3 O7_x system [1], extensive research, particularly in the field of the various sub- stitutions at the cationic sites, have been carried out in an attempt to improve the properties of these ceramics. It has been shown that the substitution of yttrium by other trivalent rare earths [2-5] (except praseodymium, cerium and terbium) has little effect on To. Partial substitution on the barium site [6-9] (25% Sr) also does not affect T,. On the other hand, copper appears vital to maintain superconducting properties close to 100 K and its substitution by other transition metals [10-13] (Zn, Ni .... ) results in a degradation of the resistive behaviour. In the same way, several workers report studies of anionic sub- stitutions in the YBa2Cu307_x system. We know actu- ally that the superconducting properties are strongly correlated with the oxygen content. Therefore, we have studied the effect of sulphur addition on these proper- ties in the YBazCu307_ x compound and later in other compounds (Y2Ba4Cu70~5 ...... ). The replacement of oxygen by sulphur should effectively lead to a change in the orbital overlapping with the copper 3d state. Moreover, the results in the literature are con- tradictory: according to some authors [14-23], the superconducting behaviour of YBa2 Cu3 O7_ ~Sy is very similar to the one of YBa2 Cu3 O7_x+v, with the sulphur atoms incorporated into the crystal lattice as shown by an appreciable expansion of all the lattice par- ameters in the sulphur doped compound. On the other hand, other authors assume that the sulphur atoms are not incorporated into the crystal lattice and make the sample multiphasic with the presence of BaSO4 [24-26]. We report in this paper a study of sulphur sub- stitution in the YBa2Cu3Ov_x compound and its effects on the structural, chemical and electrical properties. The materials with nominal compo- sitions YBa2Cu30~S~ were prepared by two different methods. 2. EXPERIMENTAL RESULTS AND DISCUSSION (i) In the first method, the samples were prepared by mixing appropriate quantities of BaCO3, CuCO3 Cu(OH)2, Y203 and CuS with y --- 0.1, 0.5 and 1. The mixture was progressively heated at 925°C in a mag- nesium oxide crucible, and the temperature was then maintained for one day with two intermediary grind- ings. After cooling (300°C h-I), the resulting mixture was reground and the structure was immediately determined by X-ray diffraction analysis. Figure 1 shows the X-ray diffraction patterns for the three different sulphur compositions. Other phases are formed when the sulphur content increases in the starting material (in the form of CuS powder). The X-ray diffraction pattern corresponding to the 1.2.3 615