Solid State Sciences 3 (2001) 31–42 Metastable solid solutions in the system ZnOCoO: synthesis by hydrolysis in polyol medium and study of the morphological characteristics Laurence Poul a , Souad Ammar a , Noureddine Jouini a, *, Fernand Fie ´vet a , Franc ¸oise Villain b a Laboratoire de Chimie des Mate ´riaux Divise ´s et Catalyse, Universite ´ Paris 7 -Denis Diderot, 2 Place Jussieu, 75251 Paris, France b Laboratoire de Chimie Inorganique et Mate ´riaux Mole ´culaires, Universite ´ Pierre et Marie Curie, 4 Place Jussieu, 75252 Paris, France Received 11 September 2000; accepted 2 October 2000 Dedicated to Professor Michel Tournoux on the occasion of his retirement Abstract Metastable solid solutions in the system ZnOCoO have been synthesized by hydrolysis of ionic zinc and/or cobalt salts in polyol medium. The solubility of Co in the zincite oxide was significantly increased (at.% Co =65) compared to that obtained under thermodynamical equilibrium (at.% Co =6.5 at 800°C). CoO was also obtained via this route. The products are made up of sub-micrometer particles. A detailed study of their morphology along with pure ZnO particle morphology was conducted. Different growth mechanisms are evidenced. © 2001 E ´ ditions scientifiques et me ´dicales Elsevier SAS. All rights reserved. Keywords: Zn 1– x Co x O; ZnO; CoO; Metastable solid solution; Polyol; Particle growth www.elsevier.com/locate/ssscie 1. Introduction Powdery oxides or metals with particles of uni- form shape and narrow size distribution lying in the sub-micrometer or nanometer size range are at present the subject of intense researches because of their specific properties. In order to prepare these finely dispersed powders several preparative chimie douce routes have been developed. Among these methods, the sol – gel pro- cess is the most used. One can distinguish between two sol – gel routes. The first involves the hydrolysis of an ionic salt in an aqueous solution. The second route corresponds to the hydrolysis of a molecular alkoxyde in an organic solvent that is generally the parent alcohol [1]. This second route has been widely used for the synthesis of oxides of elements like Ti, Si [2,3]. Indeed, the corresponding alkoxides are monomeric, soluble in alcohol and commercially available [4]. A survey of the literature shows that this route has never been employed to prepare oxides of 3d metals like Zn, Ni, Co or Fe. This is due to the fact that the corresponding alkoxides are polymeric, insoluble and therefore not commercially available. In the past decade a novel preparative route for such oxides has been developed [5,6]. It consists of the hydrolysis of an ionic salt in an organic solvent, namely a polyol. This new method offers several advantages: the use of common ionic salts instead of * Corresponding author. E-mail address: jouini@ccr.jussieu.fr (N. Jouini). 1293-2558/01/$ - see front matter © 2001 E ´ ditions scientifiques et me ´dicales Elsevier SAS. All rights reserved. PII: S1293-2558(00)01129-8