Conductivity, magnetoresistance, and specific heat of oxygen-deficient La0.67Sr0.33MnO3−α (0≤α≤0.16)

Oxygen-deficient La 0.67 Sr 0.33 MnO 3−α solid solutions have been studied. A comparison is made with the results obtained in an earlier study of a similar lanthanum-calcium manganite series. The physical characteristics of both series are accounted for as being due to a change in the Mn 3+ /Mn 4+ ratio caused by oxygen removal. The differences between the strontium and calcium series originate from differences in both the bulk properties of the original oxygen-stoichiometric materials and their texture. In the strontium series, the texture manifests itself in intergrain magnetoresistance, which exceeds in magnitude the colossal magnetoresistance caused by bulk properties of the material. Study of the oxygen-deficient La 0.67 Sr 0.33 MnO 3−α compound revealed specific features in the dependence of the electrophysical parameters on temperature and the Mn 4+ fractional content that were not observed in the La 0.67 Ca 0.33 MnO 3−α compound studied by us earlier and in La 1− x Sr x MnO 3 samples described in the literature. The physics underlying these differences is discussed. A modified phase diagram relating the phase transition temperature to the Mn 4+ fraction is proposed.