Structure of Metastable Sr.sub.0.8Dy.sub.0.2Co.sub.3 - [delta] Phases and Their Electrical and Magnetic Properties

Polycrystalline Sr.sub.0.8Dy.sub.0.2Co.sub.3 - [delta] complex cobalt oxides with a different amount of oxygen ([delta] = 0.26, 0.44, 0.46) have been prepared by solid-state synthesis. An increase in oxygen deficiency causes the brownmillerite phase to appear in the perovskite structure, which significantly changes its properties. At [delta] = 0.46, the content of the brownmillerite phase reaches 38%. A comparative analysis of the magnetic and transport properties of synthesized samples has been carried out. The asymptotic Curie temperature changes sign from positive at [delta] = 0.26 to negative at [delta] = 0.46. The magnetoresistance of the sample with [delta] = 0.46 is negative and exceeds 40% at T = 10 K. The temperature dependence of resistivity is characteristic of semiconductors, and the absolute values for samples at low temperatures differ almost tenfold.