Studies on magnesium- and titanium-substituted LaCoO₃

Abstract

Crystallographic, electrical and magnetic studies have been carried out on the Mg²⁺- and Ti⁴⁺-substituted LaCoO₃ systems, LaCo_1-xMg_xO₃ and LaCo_1-xTi_x0₃. In the magnesium system, substitution occurs up to x = 0.1, retaining the rhombohedral perovskite structure of LaCoO₃. Magnesium substitution results in a lowering of the activation energy for electrical conduction, an enhancement of the positive Seebeck coefficient and a decrease of the magnetic moment per cobalt ion, owing to the creation of Co^IV ions (holes). In the titanium system, isomorphous substitution of titanium occurs in LaCoO₃ up to x = 0.2. For x ≤ 0.1, the rhombohedral perovskite structure is retained. For x = 0.2, the composition has the cubic perovskite structure. For x > 0.2, the compounds have a distorted perovskite structure exhibiting oxidative non-stoichiometry. The resistivity and its activation energy increase with x beyond x = 0.05. Ti⁴⁺ acts as an n-type dope up to x = 0.05, beyond which the samples revert to p-type semiconductivity.