XANES Study of La_0.75-xGd_xCa_0.25MnO_3-δSolid Solutions

Abstract

A series of solid solutions La 0.75−x Gd x Ca 0.25 MnO 3−δ with 0.0 ≤ x ≤ 0.75 was prepared via carbonate precursor precipitation method. Final sintering was performed at 1250• C in oxygen flow atmosphere. The samples obtained were characterized by scanning electron microscope, X-ray diffraction measurements. Oxygen stoichiometry was analyzed by iodometric titration method. X-ray absorption spectroscopic methods of Mn L-edge and Mn K-edge X-ray absorption near edge structure were used to study oxidation state of manganese in the solid solutions and elucidate features of their local crystal structure. Orthorhombic crystal structure characteristics of the solid solutions were refined by Rietveld method. An increase in oxygen deficiency and average manganese oxidation state were found to accompany Gd concentration increase in La 0.75−x Gd x Ca 0.25 MnO 3−δ . These results are consistent with Mn L-edge X-ray absorption near edge structure spectra, where a gradual change of Mn oxidation state with Gd concentration increase was detected. Origins of oxygen deficiency La 0.75−x Gd x Ca 0.25 MnO 3−δ are discussed in terms of structural disorder caused by Gd substitution for La.

Magneto-transport study of nanocrystalline and polycrystalline manganites La0.75Ca0.25MnO3

“…Crystal structure was characterized by X-ray diffraction and XANES methods [3]. Details of magnetic and magneto-transport measurements were described separately [2].…”