Sensors and Actuators B 44 (1997) 590–594 Microstructural evolution of nanosized LaFeO 3 powders from the thermal decomposition of a cyano-complex for thick film gas sensors Maria Cristina Carotta a , Maria Angela Butturi a , Giuliano Martinelli a, *, Yoshihiko Sadaoka b , Patrizia Nunziante c , Enrico Traversa c a INFM—Dipartimento di Fisica, Uniersita’ di Ferrara, Via Paradiso 12, 44100 Ferrara, Italy b Department of Applied Chemistry, Faculty of Engineering, Ehime Uniersity, Matsuyama 790, Japan c Dipartimento di Scienze e Tecnologie Chimiche, Uniersita’ di Roma ‘Tor Vergata’, Via della Ricerca Scientifica, 00133 Rome, Italy Accepted 6 April 1997 Abstract Nanosized, single-phase perovskite-type LaFeO 3 powders are prepared by the thermal decomposition at 600°C of a hexa- cyanocomplex, La[Fe(CN) 6 ].5H 2 O. The formation of LaFeO 3 and its microstructural evolution with the temperature have been studied by simultaneous thermogravimetric and differential thermal analysis (TG/DTA), x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). LaFeO 3 is formed by the decomposition of the complex with a peculiar morphology, consisting of nanosized particles in soft agglomerates with the same size and shape of the complex grains. The nanosized particles are free of pores, making the powders suitable for application in thick film fabrication, after disruption of the agglomerates, for their use as active elements for gas sensors. Preliminary experiences are encouraging the use of this sensor for NO 2 detection in the real environment. © 1997 Elsevier Science S.A. Keywords: Thick film; Gas sensors; Nanosized; LaFeO 3 1. Introduction LaFeO 3 possesses very interesting properties (highly nonstoichiometric composition and mixed conductivity by both ion and electron migration) which make it particularly interesting for technological applications as a material for sensors. LaFeO 3 has been proposed for the detection of humidity [1,2], alcohol [3], oxygen [4], CO [5,6], and NO [7,8]. Our purpose is the development of sensors based on this material in thick film form. In fact, screen printing technology allows a reliable manu- facturing of the sensing elements, with low-cost mass production [9]. For this application, the achievement of controlled porous structures is essential. The control of the microstructure in the final products can be obtained using ultrafine, homogenously-sized ceramic powders as starting materials. The conventional method for the preparation of LaFeO 3 is the solid-state reaction at high temperatures of LaO 3 and Fe 2 O 3 , as in general for the mixed oxides. Given that this method is performed at high temperatures, the powders obtained are coarse, with a non-uniformity of particle size and shape, have multiphase character and show, in certain cases, loss of stoichiometry due to the volatilisation of a reactant [10]. The synthesis of ultrafine and chemically pure powders of mixed oxides can be performed by develop- ing innovative chemical methods [11]. Chemical pro- cessing methods permit to lower the synthesis temperature of mixed-metal oxides and to improve homogeneity and reproducibility of the ceramic prod- ucts. The preparation of LaFeO 3 perovskite-type oxide by the thermal decomposition at low temperatures of a hexacyanocomplex, which is readily precipitated from aqueous solution, has been firstly proposed by Gal- lagher in 1968 [12]. Recently, some of the authors of this paper have confirmed that pure LaFeO 3 powders, with relatively high specific surface area and ultrafine * Corresponding author. Tel.: +39 532 781811; fax: +39 532 781810; e-mail: martinelli@vaxfe.fe.infn.it 0925-4005/97/$17.00 © 1997 Elsevier Science S.A. All rights reserved. PII S09 2 5 -4 005(97)00 1 77 - 9