Effects of inhomogeneous oxygen content in $(La,Gd)0.7Ca0.3MnO3+δ$ perovskites Available to Purchase

Magnetoresistance properties of compounds with the same formula $La0.7−xGdxCa0.3MnO3+δ$ (⁠$x=0,$ 0.04) but synthesized by the solid-state reaction method from different starting materials are studied. Nearly stoichiometric compounds are obtained when $La(OH)3$ is used for sample preparation. However, under the same condition, $La2O3$ causes considerable oxygen deficiency in resulting samples, characterized by a broad metal–semiconductor transition far below the magnetic transition. Inhomogeneous distribution of the oxygen content in compounds (an inhomogeneity beyond the detection of powder x-ray diffraction) can occur when both $La2O3$ and $La(OH)3$ coexist in the starting materials, leading to two metal–semiconductor transitions which are obviously developments of those in compounds prepared respectively from $La2O3$ and $La(OH)3,$ and one magnetic transition corresponding to the upper resistive transition.