Effect of oxygen annealing on the electrical properties of La1-xSrxMnO3+δ:: single crystals around the compositional metal-insulator transition -: art. no. 184419

We have prepared La1-xSrxMnO3+delta single crystals for not only oxygen-deficient (delta <0) but also oxygen-excess (<delta>>0) regions. Although resistivity rho (T) is less sensitive to delta in the metallic region x greater than or equal to0.175, it is drastically reduced by increase of delta around the metal-insulator transition x = 0.14-0.16, where rho (T) is insulating for delta <0 but it becomes metallic for <delta>>0. The wide ferromagnetic-insulating phase so far reported may be mainly due to the deficiency and/or inhomogeneity of the oxygen ions. The structural phase transitions observed for delta <0 disappear for <delta>>0, suggesting the relation of the oxygen vacancies to these transitions. We discuss the present results in terms of the defect chemistry.