Effects of oxygenation processes on (Nd,Gd)-Sr 2 RuCu 2 O x synthesis Antonio Vecchione a, * , Marcello Gombos a , Consiglia Tedesco b , Daniela Sisti b , Sivaperumal Uthayakumar c,1 , Sandro Pace c a INFM, Coherentia U.d.R. Salerno and Dipartimento di Fisica, ‘‘ER Caianiello’’, Universit  a di Salerno, via Salvador Allende, I-84081 Baronissi (Salerno), Italy b Dipartimento di Chimica, Universit  a di Salerno, via S. Allende, I-84081 Baronissi (Salerno), Italy c INFM, U.d.R. Salerno and Dipartimento di Fisica, ‘‘E.R. Caianiello’’, Universit  a di Salerno, via Salvador Allende, I-84081 Baronissi (Salerno), Italy Abstract In this work we report on the effect of oxygenation processes on the structure and composition of GdSr 2 RuCu 2 O x andNdSr 2 RuCu 2 O x compounds.ByX-raydiffractionanalysisitresultsthatthetetragonalGd-basedcompoundbegins to form after prolonged time, while a progressive improvement of cubic Nd-based samples is observed as impurity peaks disappear. Evolution of crystalline structure after oxygen annealing treatments has been studied too. Ó 2003 Elsevier Science B.V. All rights reserved. Keywords: Rutheno-cuprate materials; Synthesis processes; X-ray powder diffraction 1. Introduction RESr 2 RuCu 2 O x (RE-1212) rutheno cuprates have attracted much attention due to the co-existence of fer- romagnetismandsuperconductivityinthesenewclassof compounds [1,2]. After the report by Bauernfeind et al. [3], many efforts are being made to synthesize these compounds. We have already reported that absence of superconductivity in the NdSr 2 RuCu 2 O x (Nd-1212) compoundisduetotheintermixingofcationsofCu/Ru site as well as Nd/Sr ions producing disordered network of CuO 2 and RuO 2 planes [4]. This disordered network inhibits superconductivity and magnetic ordering. The establishment of the superconducting state has turned outtobestronglydependentonthesamplequality[1].A better understanding of the relation between the phase formation and the oxygenation process is necessary in order to improve the reliability and repeatability to synthesize these new class of compounds. In this report, weinvestigatetheeffectofoxygenationonthestructural properties of (Nd,Gd)-1212 to get more insight into the phase formation of these compounds. 2. Results and discussion Polycrystalline samples of Nd and Gd-1212 were prepared by mixing the stoichiometric amounts of Gd 2 O 3 orNd 2 O 3 andSrCO 3 ,CuO 2 andRuO 2 .Wehave prepared two batches of Gd-1212 samples. The first batch of Gd-1212 sample was calcinated in air for 10 h at960 °CandasecondbatchofGd-1212wascalcinated at960 °C for 17 h. After calcinating the two batches the samples were reground, milled and annealed in argon flow at 1020 °C for 10 h. Finally the samples were oxy- genated with a procedure made by several cycles of * Corresponding author. Fax: +39-089-953804. E-mail address: vecchione@sa.infn.it (A. Vecchione). 1 Permanent address: Crystal Growth Centre, Anna Univer- sity, Chennai 600 025, India. 0921-4534/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0921-4534(02)02530-3 Physica C 388–389 (2003) 391–392 www.elsevier.com/locate/physc