On the effects of Ga³⁺ and La³⁺ ions in MgCu ferrite: Humidity‐sensitive electrical conduction

Abstract

Pure and gallium or lanthanum substituted MgCu ferrites, Mg 0.5 Cu 0.5 Fe 2-x M x O 4 (with x = 0 or 0.2 and M = La or Ga) have been prepared by solid state reaction. Sintering experiments were carried out at different temperatures between 900 and 1100°C. The phase composition and lattice parameters were determined by XRD, while the effect of Ga and La substitutions on the granular structure was studied by SEM. Experimental results revealed that the densification behaviour and some physical properties are in close relation with the structural changes of pure ferrite caused by the presence of La and Ga substitutions. The gallium containing compound, Mg 0.5 Cu 0.5 Fe 1.8 Ga 0.2 O 4 , is monophasic and contains a great number of pores, whereas the lanthanum containing compound, Mg 0.5 Cu 0.5 Fe 1.8 La 0.2 O 4 , is biphasic and exhibits a high density. The humidity characteristics show that the gallium ion enhances the humidity sensitivity of the MgCu ferrite sintered at 1000°C. This interesting effect is promising for the future of the Ga-substituted MgCu ferrite to be used as sensitive material for fabrication of ceramic humidity sensors. IntroductionMixed ferrite attracted much attention because of their vast applications in a wide range, from microvawe to radio frequencies, such as microwave devices, computer memories and magnetic recording [1]. In many applications, they play an useful role because of their high resistivity and low eddy current losses . During the last years, many kinds of oxide ceramics have been investigated as materials for humidity sensors used in automatic humidity controlling systems [2 -9]. Basically, ceramic sensors can detect humidity on the basis of the change of the surface electrical conductivity by vapour adsorption.A particular attention was paid to Mg-ferrite (MgFe 2 O 4 ) [4,10,11]. This ceramic sintered at high temperatures is essentially more stable physically, chemically and thermally than other materials used for conventional humidity sensors [2]. A great advantage of using ferrites is their porous structure. For an humidity ceramic sensor it is very important that the fraction of open pores with respect to closed pores should be increased and the distribution of all open pores should be optimized [8,12]. Microstructure and intrinsic conductivity are found to be two key parameters which affect the sensor effect in oxide ceramics.The present study was concentrated on a magnesium-copper ferrite. A very limited amount of work is reported on this ferrite, although it is an inexpensive material and does not requires special conditions for preparation. Also, this ferrite is characterised by a high resistivity, being preferred in many electronic applications.

Synthesis, characterization and magnetic properties of La3+ added Mg–Cd ferrites prepared by oxalate co-precipitation method

“…Samy [18] has studied magnetic and electrical properties of R = La, Nd, Sm, Gd substituted Cu-Zn ferrite and reported decrease in saturation magnetization and grain size. An increase in resistivity and porosity of La 3+ substituted Mg-Cu ferrite has been reported by Rezlescu et al [19] and further they showed that conduction in ferrite is sensitive to microstructure. Roy et al [20,21] have studied the magnetization measurements of La 3+ substituted Ni-Cu-Zn ferrite using different techniques and reported an increase in saturation magnetization, resistivity and permeability.…”

Synthesis of metal ferrite (MFe2O4, M = Co, Cu, Mg, Ni, Zn) nanoparticles as humidity sensor materials

“…The particles are lumped and become compact. The SEM image of magnesium ferrite indicated that the distribution of grain size obtained by this process is smaller than that obtained through the ceramic route [20,21]. Aggregation of smaller grains was observed with the formation of lesser pores.…”

Investigations on structural, electrical and dielectric properties of yttrium substituted Mg-ferrites

“…Rezlescu et al [7] reported the influence of Ga 3 þ and La 3 þ in Mg-Cu ferrites. A systematic study of the dielectric properties of Mg-Zn ferrites as a function of frequency and composition has been reported by Mansour [8].…”