Abstract. Experimental data are shown for the influence of substituting quadrivalent ions on the concentration phase transitions "rhombohedral-orthorhombic structure" and "semiconductor-metal" in ceramic manganites of specifically designed system La 3+ c=0.15, 0.17, 0.19; 0.025x0.125). Regularities in the concentration dependences of unit cell volume, saturation magnetization, Curie point, and resistivity were established. Ge-substituted manganites had essentially higher values of magnetization and Curie temperature than analogous compositions with Ti. The approach to the interpretation of experimental results is discussed in terms of electron configurations and ionic radii of substituents taking into account oxygen nonstoichiometry and cation vacancies.
Regularities of the inuence of quadrivalent ions and oxygen concentrations on the structural characteristics, saturation magnetization, Curie point, temperature dependence of electrical conductance of ceramic manganites La1−c−xSrc+xMn1−xMe 4+x O3+γ (Me = Ti, Ge; 0.17 ≤ c ≤ 0.35; 0.025 ≤ x ≤ 0.125) were established. The relation between experimental data on lattice parameters, electromagnetic properties and crystal chemistry characteristics (nonstoichiometry index, concentrations of ions residing at dierent charge states) was determined using the modied model of eective cationanion distances. The data obtained provide some evidence that in Ti-containing manganites when Sr concentration is more than 0.375, single-charged oxygen ions can arise after reductive annealing.
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