CO 2 and O 2 sensing behavior of nanostructured barium-doped SmCoO 3 Emilio Delgado, Carlos R. Michel ⁎ Departamento de Física CUCEI. Universidad de Guadalajara, Blvd. M. García Barragán 1421, Guadalajara, Jalisco, 44410, México Received 20 July 2005; accepted 25 November 2005 Available online 19 December 2005 Abstract Single-phase perovskites, Sm 1-x Ba x CoO 3 (x = 0, 0.1), were prepared by a simple aqueous solution method using stoichiometric amounts of the corresponding nitrates and citric acid. X-ray diffraction showed that the introduction of barium reduced the temperature of formation of the perovskite and yielded nanostructured Sm 0.9 Ba 0.1 CoO 3 . The evaluation of nanostructured Sm 0.9 Ba 0.1 CoO 3 as a gas sensor material was made through the electrical characterization of sintered thick films, in flowing O 2 and CO 2 . The results clearly indicate good sensitivity to these gases at 373 °C and 410 °C, respectively. © 2005 Elsevier B.V. All rights reserved. Keywords: Nanomaterials; Perovskites; Sensors; Sol-gel preparation 1. Introduction Intensive scientific research has been focused in the development of nanoporous and nanostructured inorganic materials. For applications involving physicochemical interac- tions between solid surfaces and gas species, such as environmental gas sensors, nanostructured materials offer an enormous potential. To obtain nanostructured materials, various synthetic routes have been successfully tested, such as reverse micelles, microemulsions, sol-gel and coprecipitation to name a few [1–7]. However, only a limited number of nanostructured inorganic materials have been studied in depth, such as TiO 2 , SnO 2 , SiO 2 , ZnO and few more. Cobaltites with the perovskite structure, M 1-x Sr x CoO 3 (M = La or Nd), are currently used as electrodes for solid oxide fuel cells and ceramic membranes for oxygen permeation and gas sensors, due to their high mixed ionic–electronic conductivity and good chemical stability at high temperature [8–13]. In these oxides, the partial substitution of the rare-earth element by an alkaline-earth metal, produces a mixed-valence state in cobalt: Co 2+ and Co 3+ , which is related to the enhancement of electrical conductivity. The goals of this work were the preparation of nanostructured oxides of the solid solution: Sm 1-x Ba x CoO 3 by a solution method and the characterization of the as-calcined powders by X-ray powder diffraction and scanning electron microscopy. To test these materials as environmental gas sensors, the change of electrical resistance with temperature, and the dynamic response of resistance at a high temperature, were performed on thick films of Sm 0.9 Ba 0.1 CoO 3 . These experiments, made in flowing CO 2 and O 2 , showed the good sensitivity of this perovskite to these gases. 2. Experimental The starting reagents used for the preparation of the perovskites, Sm 1-x Ba x CoO 3 (x =0, 0.1, 0.13), were Sm (NO 3 ) 3 ·6H 2 O (Alfa Aesar), Ba(NO 3 ) 2 (Alfa Aesar) and Co (NO 3 ) 2 ·6H 2 O (J. T. Baker). Stoichiometric amounts of the salts were dissolved in deionized water containing 0.1 mol of citric acid (PQM). The mixtures were slowly dried at 75 °C for approximately 3 h. The precursor powders were calcined in air, from 700 to 900 °C, in a muffle-type furnace by heating at 100 °C/h followed by a 6-h dwell. The calcined powders were analyzed by X-ray powder diffraction (XRD), using a Rigaku Miniflex apparatus (Cu K α radiation); the diffraction angle (2θ) was scanned from 5° to 60°. The morphology of the oxides was observed by scanning electron microscopy (SEM) using a Jeol JSM-5400LV Materials Letters 60 (2006) 1613 – 1616 www.elsevier.com/locate/matlet ⁎ Corresponding author. Tel./fax: +52 33 33 45 41 47. E-mail address: michelucr@yahoo.es (C.R. Michel). 0167-577X/$ - see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2005.11.080