Conduction mechanism in Y3-2xCa2xFe5-xVxO12 garnet ferrites

A series of polycrystalline garnet ferrites with composition Y3-2xCa2xFe5-xVxO12 (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0), were prepared by the standard ceramic technique to study the effect of Ca2+ and V5+ ions substitution on their DC electrical conductivity, thermoelectric power, charge carrier concentration and charge carrier mobility at different temperatures. It was found that the DC electrical conductivity increases linearly with increasing temperature ensuring the semiconducting nature of samples. The lines representing the temperature dependence of sigma(dc) are broken at two-phase transition temperature (T-sigma1, T-sigma2 = T-C) giving three distinct regions (1, 11 and 111). The activation energy for electrical conduction increases going from ferrimagnetic state (regions I and 11) to paramagnetic state (region 111) through the transition temperature Tsigma(2) (Curie temperature). It also increases going from region I to region 11 thorough the temperature T-sigma1. The dc electrical conductivity does not vary uniformly with Ca2+ and V5+ ion substitution. The values of the thermoelectric power were positive for samples of 0.0 less than or equal to x less than or equal to 0.6 indicating that the majority of the carrier are holes in these samples while it were negative for samples of x greater than or equal to 0.8 indicating that the majority of charge carriers are electrons in this samples. Using the values of the DC electrical conductivity and thermoelectric power, the values of the charge carrier concentration and the charge carrier mobility were calculated. (C) 2004 Elsevier SAS. All rights reserved.