Synthesis of Nanocrystalline Tetragonal Zirconia by a Polymeric Organometallic Method Antonio L. Quinelato, 1 * Elson Longo, 2 Edson R. Leite 2 and Jose  A. Varela 3 1 CNEN/COLAB, Poc ¸os de Caldas, MG, 37701-970 Brazil 2 Departamento de Quı ´mica, UFSCar, Sa ˜o Carlos, SP, 13565-905 Brazil 3 Instituto de Quı ´mica, UNESP, Araraquara, SP, 14800-900 Brazil A polymeric precursor method based on the Pechini process was successfully used to synthe- size zirconia–12 mol% ceria ceramic powders. The influence of the main process variables (citric acid—ethylene glycol ratio, citric acid— total oxides ratio and calcination temperature) on phase formation and powder morphology (surface area and crystallite size) were investi- gated. The thermal decomposition behavior of the precursor is presented. X-ray diffraction (XRD) patterns of powders revealed a crystal- line tetragonal zirconia single-phase, with crys- tallite diameter ranging from 6 to 15 nm. The BET surface areas were relatively high, reaching 95 m 2 g À1 . Nitrogen adsorption/desorption on the powders suggested that nonaggregated powders could be attained, depending on the synthesis conditions. Copyright # 1999 John Wiley & Sons, Ltd. Keywords: Pechini process; zirconia; ceramic; x-ray diffraction Received 4 April 1998; accepted 1 October 1998 INTRODUCTION Zirconia is an important ceramic material widely employed in differing fields such as refractories, cutting tools, oxygen sensors and electrolytes. 1 Pure zirconia undergoes a reversible diffusionless martensitic monoclinic–tetragonal phase transfor- mation at about 1200 °C. 1,2 This transformation is associated with a large volume change, so that severe cracking often appears if ceramics are cycled through the transition temperature, which renders the material useless for structural applications. Thus, during normal processing the high-tempera- ture tetragonal phase must be stabilized at room temperature to avoid this problem. The stabilization is achieved by making solid solutions with several oxides. 1 Ceria-doped zirconia can result in a single- phase tetragonal structure, which possesses excel- lent mechanical properties. The tetragonal phase stability is dependent on the solubility limit described in the temperature–composition equili- brium phase diagram. 3 The alloy containing 12 mol% CeO 2 was found to be more attractive for its high fracture toughness. 4 The crystallite size effect on the stabilization of tetragonal zirconia has been observed. 5,6 Garvie 7 explained this effect by taking into account that the surface energy of the tetragonal phase is less than that of the monoclinic structure. 8 Thus, the tetragonal form is more stable in small crystallites and, if a critical crystallite size is exceeded, the tetragonal particles are transformed to the monoclinic phase. Recently, wet-chemical methods have been employed with the aim of producing ceramic powders with high purity, compositional homo- geneity, precise stoichiometry and fine particles. Among different methods, the application of polymeric precursors based on the process origin- ally outlined by Pechini 9 has been used in the preparation of a wide variety of ceramic oxides, such as titanates, 10,11 perovskites, 12–15 alumi- nates, 16 spinels 17 and superconductors. 18,19 In the Pechini process described in the original patent, 9 an a-hydroxycarboxylic acid, preferably citric acid, is used to chelate various cations by forming a polybasic acid. In the presence of a polyhydroxy alcohol, normally ethylene glycol, these chelates react with the alcohol to form ester and water by-products. When the mixture is heated, APPLIED ORGANOMETALLIC CHEMISTRY Appl. Organometal. Chem. 13, 501–507 (1999) Copyright # 1999 John Wiley & Sons, Ltd. CCC 0268–2605/99/070501–07 $17.50 * Correspondence to: Antonio L. Quinelato, CNEN/COLAB, Poc ¸os de Caldas, MG, 37701-970 Brazil. Contract/grant sponsor: FINEP. Contract/grant sponsor: CNPQ. Contract/grant sponsor: CNEN/COLAB.