Preparation by sol±gel, structure and superconductivity of pure and ¯uorinated LaBa 2 Cu 3 O 7d R. Suryanarayanan a, * , R. Nagarajan b,1 , H. Selig b , L. Ben-Dor b a Laboratoire de Physico-Chimie de l'Etat Solide, CNRS UMR 8648, B^ at. 414, Universit e Paris-Sud, 91405 Orsay, France b Department of Inorganic and Analytical Chemistry, Hebrew University, Jerusalem 91904, Israel Received 26 September 2000; received in revised form 5 March 2001; accepted 12 March 2001 Abstract Whereas an enormous amount of literature exists describing the preparation of the well known high T c supercon- ductor YBa 2 Cu 3 O 7 as a single phase compound with a transition temperature T c 92 K, very few reports have been published on the preparation of the rare earth analog compound LaBa 2 Cu 3 O 7 . This report describes the preparation of LaBa 2 Cu 3 O 7 compound by sol±gel technique. A single phase compound that showed an orthorhombicity of 5 10 3 and a T c 93 K was obtained. The ¯uorination of this compound did not alter the values of neither the lattice pa- rameters nor the T c . Ó 2001 Elsevier Science B.V. All rights reserved. Keywords: LaBaCuO; Fluorination; Magnetization; Sol±gel 1. Introduction Soon after the discovery of the high tempera- ture superconductivity by Bednorz and M uller [1] the ®rst Y-123 cuprate YBa 2 Cu 3 O 7 ) was prepared and characterized by Wu et al. [2]. The compound YBa 2 Cu 3 O z YBCO) has an orthorhombic crystal structure with oxygen content z close to 7. Imme- diately it was shown by several authors that single phase compounds can be formed by substitution of Y by the rare earths. The rare earth cuprates LnBa 2 Cu 3 O 7 Ln lanthanides) are isostructural compounds and their superconducting critical temperature T c is above 90 K except in the case of PrBa 2 Cu 3 O 7 which does not exhibit superconduc- tivity, though some reports have appeared recently indicating the appearance of superconductivity in this compound [3±6]. Normally, these compounds were prepared by solid state sintering reaction at 980°C from the respective carbonates or oxides followed by oxygen annealing at lower tempera- tures. The sol±gel route was soon applied to pre- pare some of these superconductors [7±10]. This method was shown to produce homogeneous, single phase materials. Whereas most of the lanth- anide cuprates can be prepared relatively easily devoid of any major impurity phases with a T c close to 90 K, several authors have encountered diculties [11,12] in the synthesis of LaBa 2 Cu 3 O 7 as pointed out by Wada et al. [13] and Izumi et al. [14]. The main diculties that one encounters in Physica C 361 2001) 40±44 www.elsevier.com/locate/physc * Corresponding author. Tel.: +33-1-6915-4796; fax: +33-1- 69-15-47-97. E-mail address: ramanathan.suryan@lpces.fr R. Suryana- rayanan). 1 Present address: Department of Chemistry, Oregon State University, Corvallis, OR-97331, USA. 0921-4534/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII:S0921-453401)00290-8