Effects of Nonstoichiometry and Plastic Deformation on Charge and Spin States of Cobalt Ions in LnBaCo2BaO5.5 – δ (Ln = Tb, Eu): Soft X-ray Absorption Spectroscopy Studies

Abstract

We present results of soft X-ray absorption spectroscopy studies of nonstoichiometric Tb_1 ‒ yBa_{1 +y}Co_{2 –x}O_{5.5 – δ} cobaltites and EuBaCo₂O_5.5 cobaltite powders subjected to mechanical impact (milling in a ball mill). It was established that in octahedra of Tb_1 – yBa_1 + yCo_2 – xO_5.5 – δ cobaltates Co³⁺ ions are in the high spin state. In EuBaCo₂O_5.5 powder after milling in a ball mill, a surface area (5–10 nm) of particles was found to be decomposed into Co₃O₄, BaCO₃, and EuCoO₃ phase components. A knowledge of the low-spin state of Co³⁺ ions in EuCoO₃ and Co₃O₄ and possibilities of surface-sensitive soft X-ray absorption spectroscopy have allowed to determine the composition of the EuBaCo₂O_5.5 sample (subjected to ball milling) near its surface, which is inaccessible to standard X-ray phase analysis.