Effects of some ionic substitutions on sintering, structure and humidity sensitivity of MgCu ferrite

Abstract

The effect of Y3+, La3+, Ga3+, Ti4+ and Nb5+ ions on the physical properties of stoichiometric Mg0.5Cu0.5Fe2O4 ferrite is investigated. The substitutions partially replace the Fe3+ ions and the chemical formula of the investigated ferrites is Mg0.5Cu0.5Fe2−xMe3x/nO4, where Me = Y, La, Ga, Ti and Nb, x = 0 and 0.2, and n is the valence of Me. It is found that the magnetic and electrical properties of MgCu ferrite change with the substituent species. La ions play an important role in increasing the density, while Nb ions favour ferritization at low temperature. Ga substitution increases the electrical resistivity and saturation magnetization, but decreases the density. The humidity sensitivity of the samples with and without substitutions is also investigated. The electrical resistance of Ga-containing ferrite decreases by two orders of magnitude when the relative humidity increases from 33 to 100%. The results are discussed in terms of microstructural changes induced by the substitutions. Conclusions are drawn concerning the optimization of response time to humidity change for the development of ceramic humidity sensors which are more chemically and thermally stable than polymeric sensors. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)