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

We have prepared La1-xSrxMnO3+delta single crystals for not only oxygen-def icient (delta <0) but also oxygen-excess (<delta>>0) regions. Although resi stivity 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 arou nd the metal-insulator transition x = 0.14-0.16, where rho (T) is insulatin g for delta <0 but it becomes metallic for <delta>>0. The wide ferromagneti c-insulating phase so far reported may be mainly due to the deficiency and/ or inhomogeneity of the oxygen ions. The structural phase transitions obser ved for delta <0 disappear for <delta>>0, suggesting the relation of the ox ygen vacancies to these transitions. We discuss the present results in term s of the defect chemistry.