Phase Diagram and EXAFS Study of La_0.7Ca_0.3−xBa_xMnO₃ Manganites

Abstract

The phase diagram and local structure of La_0.7Ca_0.3−xBa_xMnO₃ (x=0;0.03;0.06;…;0.3) lanthanum manganites were studied. The Curie temperature, T_c, of the compositions showed a sharp change near the concentrational structural orthorhombic–rhombohedral phase transition. Maximums of dispersion, σ_Mn–O², and asymmetry, σ_Mn–O³, of pair distribution function for the Mn–O bond distances of MnO₆ octahedron on x-dependence were observed by extended X-ray absorption fine structure (EXAFS) analysis. The maximum of σ_Mn–O² is caused by increase of dynamic rms displacements of Mn–O bond distances near the T_c. The observed x dependence of σ_Mn–O³ reflects the reduction of charge carriers mobility at approaching to T_c.