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

We present results of soft X-ray absorption spectroscopy studies of nonstoichiometric Tb 1 ‒ y Ba 1 + y Co 2 – x O 5.5 – δ cobaltites and EuBaCo 2 O 5.5 cobaltite powders subjected to mechanical impact (milling in a ball mill). It was established that in octahedra of Tb 1 – y Ba 1 + y Co 2 – x O 5.5 – δ cobaltates Co 3+ ions are in the high spin state. In EuBaCo 2 O 5.5 powder after milling in a ball mill, a surface area (5–10 nm) of particles was found to be decomposed into Co 3 O 4 , BaCO 3 , and EuCoO 3 phase components. A knowledge of the low-spin state of Co 3+ ions in EuCoO 3 and Co 3 O 4 and possibilities of surface-sensitive soft X-ray absorption spectroscopy have allowed to determine the composition of the EuBaCo 2 O 5.5 sample (subjected to ball milling) near its surface, which is inaccessible to standard X-ray phase analysis.