Thermal properties of GdSr 2 RuCu 2 O 8d based mixtures in the GdSr 2 RuO 6 –CuO pseudo-binary system Marcello Gombos * , Regina Ciancio, Antonio Vecchione, Sandro Pace Laboratorio Regionale Supermat CNR-INFM Via Salvador Allende, I-84081 Baronissi, Italy Dipartimento di Fisica ‘‘E.R.Caianiello’’, Universita ` di Salerno, Via Salvador Allende, I-84081 Baronissi, Italy Available online 27 March 2007 Abstract GdSr 2 RuCu 2 O 8d (Gd1212) rutheno-cuprate compound is widely studied because it shows the coexistence of superconductivity and highly anisotropic magnetic ordering in the same cell. Anyway the nature of the magnetic ordering is still debated and the fabrication of macroscopic samples oriented along a crystallographic axis, that could help to clarify its details, appears to be quite difficult. For this reason, accurate investigation on Gd1212 incongruent melting reaction, producing liquid copper oxide and the solid GdSr 2 RuO 6 (Gd1210), appears to be necessary to improve the fabrication of crystallographically oriented bulk superconducting samples. Thermo-gravimetric and differential thermal measurements were performed to analyse the thermal behaviour up to 1200 °C and the melt- ing temperatures of different mixtures of Gd1212 with Gd1210 or CuO, in view to perform a scan of the whole CuO–Gd1212–Gd1210 coexistence line of the Gd–Sr–Ru–Cu–O phase diagram. Dependence on the atmosphere and the formation of different spurious phases was also studied. Ó 2007 Elsevier B.V. All rights reserved. Keywords: Rutheno-cuprates; Bulk materials; Thermal properties; Melting reaction; High temperature superconductors 1. Introduction The rutheno-cuprate compound GdSr 2 RuCu 2 O 8d (Gd1212), has recently been widely studied [1] because it shows the coexistence, in the same cell, of superconduc- tivity, correlated to Cu planes, and highly anisotropic magnetic ordering, due to Ru planes [2]. Canted anti- ferromagnetism [3], may explain well the coexistence of these phases but the real nature of the magnetic ordering is still debated. The fabrication of large oriented supercon- ducting samples, that could help to clarify its properties, appears to be quite difficult. The unavailability of single crystals (SC) makes relevant the fabrication of samples by melt texturing (MTG) techniques. The first hypothesised melting peritectic reaction of Gd1212 [4] was very similar to Y123, with GdSr 2 RuO 6 (Gd1210) in the role of Y211 and L(Cu) a Cu-rich liquid: Gd1212 = Gd1210 + L(Cu) ð1Þ Another proposed reaction, whose occurrence was ob- served in high temperature Gd1212 processing in O 2 atmo- sphere [5], is due to the high volatility of Ru: Gd1212 = GdSr 2 Cu 2 O y (Gd1202) + RuO 2 (gas) ð2Þ Anyway, oriented 0.5 mm size samples have been obtained, from Gd1212–Gd1210 precursor powders, by Top-Seeding MTG in air by our group [6]. In these samples CuO pro- duction was observed, but the initial composition was glob- ally preserved [7], suggesting that there is an interval of temperature and O 2 partial pressure pO 2 in which reaction (1) is dominant over (2). A better understanding of high temperature behaviour of Gd1212, is necessary to improve the fabrication of bulk MTG samples and SCs. 0921-4534/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2007.03.125 * Corresponding author. Address: Laboratorio Regionale Supermat CNR-INFM Via Salvador Allende, I-84081, Baronissi, Italy. Tel.: +39 089 965 381; fax: +39 089 965 275. E-mail address: gombos@sa.infn.it (M. Gombos). www.elsevier.com/locate/physc Physica C 460–462 (2007) 522–523