Effects of aging on the electrical resistivity of La1-xBxCoO3 perovskites (B = Sr, Ca, Ba; 0.20 <= x <= 0.30)

A study of the reliability of the title compounds as a basis for magnetores istive sensors is presented. For this purpose we have carried out long-term systematic studies of the evolution of the resistive and magnetic properti es of samples synthesized by both ceramic and wet chemical routes, allowing them to age during several months. It is observed that, although the magne tic properties remain unaltered, their resistivity does change appreciably. With time, samples that are initially metallic over all the measured tempe rature range (T < 300 K), change to semiconductor-like behaviour at low tem peratures and above their ferromagnetic to paramagnetic phase transition te mperature, giving rise to a 'reentrant semiconducting behaviour' with assoc iated high electrical noise, relaxation effects of the resistivity and even diodic behaviour. (C) 2000 Elsevier Science S.A. All rights reserved.