A.N. Petrov

Conductivity and carrier traps in La1−xSrxCo1−zMnzO3−δ (x=0.3; z=0 and 0.25)

Abstract Measurements of the equilibrium oxygen content, electrical conductivity and thermopower in the perovskite-like solid solution La 0.7 Sr 0.3 Co 1– z Mn z O 3− δ ( z =0 and 0.25) as a function of the temperature and oxygen partial pressure are used to determine the temperature dependence of the conductivity and thermopower at different values of the oxygen deficiency. A model for a hopping conductor with screened charge disproportionation is applied for the data analysis in combination with trapping reactions of n- and p-type carriers on local oxygen vacancy clusters and manganese cations, respectively. Changes in the ratio of n-type to p-type mobility are due to variations in oxygen vacancy concentration and manganese content, while the energetic parameters governing charge disproportionation of the trivalent cobalt cations and formation of vacancy associates are shown to be essentially invariable. These calculated charge carrier site occupancies are used to model temperature variations of the electrical properties in La 0.7 Sr 0.3 Co 1− z Mn z O 3− δ in favorable correspondence with experimental observations.

Crystal and defect structure of the mixed oxides LaMn1−zCuzO3±y (0≤z≤0.4)

Abstract The crystal structure and nonstoichiometry of the mixed Cu-doped lanthanum manganates LaMn1−zCuzO3±y (0≤z≤0.4) have been investigated by powder X-ray diffraction (PXD) and powder neutron diffraction (PND). The samples quenched in air from 1173 K to room temperature were crystallized in the orthorhombic structure (space group Pbnm). The oxygen positions, interatomic distances and occupancies have been refined based on the PXD and PND data. According to the refinement, mixed oxides LaMn1−zCuzO3±y with 0≤z≤0.2 exhibit full occupancies of the oxygen sites (O1 and O2) and deficiency of the La-sites. Oxygen nonstoichiometry in LaMn1−zCuzO3±y samples with values of z ranging from 0 to 0.3 were studied as a function of temperature (1150–1450 K) and oxygen partial pressure (10−3.5–1 atm) by means of thermogravimetry (TG). The absolute values of the oxygen nonstoichiometry (y) were determined by a full reduction in hydrogen and iodometric titration. A defect model describing experimental data is discussed.