Effects of Structural Disorder and Charge Carriers on the Magnetic and Transport Properties of Sr0.7R0.3CoO3-δ (R = Y or Dy0.45Er0.55)

Research into the magnetic and transport properties of Sr0.7R0.3CoO3-δ (R = Y or Dy0.45Er0.55) having tetragonal I4/mmm symmetry with oxygen-deficient CoO2(1-δ) (001) planes alternating with CoO2 planes, as in the brownmillerite structure, has shown that the localized 3d6 Co(III) configurations are not easily oxidized and that the n-type conduction is not realized owing to the small polaron Co(II). A ferromagnetic transition temperature decreases with increasing oxygen deficiency as well as with increasing disorder at the R site. The electrical resistivity (ρ) decreases with increasing carrier concentration (n), whereas ρ is independent of the R-site disorder. The thermoelectric power, on the other hand, varies with both n and the disorder. Although the phonon contribution to the thermal conductivity is suppressed, the polaronic conduction makes these compounds unsuitable for thermoelectric-power applications.