Sol-gel preparation and transport properties of a tin oxide

Abstract

Much work has already been carried out concerning the preparation and study of tin (IV) oxide, alone and combined with other oxides, for applications related to electrical and catalytic properties. The methods of preparation have included: (i) coprecipitation of hydroxides or oxalates starting from diluted salts; (ii) solid state reactions, by decomposition of carbonates, hydroxides; (iii) deposits by vapour phase deposition; and (iv) oxidation of SnO (e) in SnO2 by epitaxial growth. It has been noticed that the properties related to this oxide depend on the texture of the material. For this reason the sol-gel procedure was used to prepare such a compound. Generally the gel is formed by peptisation (with nitric acid) of Sn(OH)4 obtained after action on tin chloride by ammonia [1-3]. The study of these ge][s has shown that there is a temperature dependent structural evolution [3, 4] with oxygen deficient oxide [5]. Within this scope we have prepared a pure gel using a new method, the hydrolysis of a tin (II) alkoxide, and compared its structure to other gels. We have studied this gel by the method of complex permittivities. In fact, for a long time, dielectric loss measurements have been the basis of various investigations on many chalcogenides and a few oxides [6, 7]. The results obtained have usually been interpreted by theoretical models using the concept of charge carriers hopping between localised sites. Experimental data of the a.c. conduction as a function of frequency have often exhibited the following behaviour [6-10]: % = + (1) where Odc is the conductivity in direct current; o-' (co), the real part of the polarisation conductivity, is related to the frequency, f, by the expression: cr'(co) = Ac0' (co = 2zcf) where A and s are constants at a given temperature. In this work the a.c. conductivity, as a function of frequency and temperature of the oxide was measured. The a.c. conductivity data were analysed using a numerical approach described previously [11]. The results showed that the a.c. behaviour of this poorly organised tin oxide could be described by a well-known theoretical model related to thermally activated electron hopping. The method used for the synthesis of the tin alkoxide