Phase transitions in frustrated slightly nonstoichiometric ErBaCo4O7 + x (x ≈ 0 and 0.03) cobaltitesстатья
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Дата последнего поиска статьи во внешних источниках: 21 октября 2020 г.
Аннотация:The results of the first experimental studies on the structural (lattice parameters) and elastic characteristics of ErBaCo4O7 + x cobaltites in the range of structural and magnetic phase transitions are presented. The samples characterized by a small oxygen excess x are studied using different thermal treatments. It is found that the parameter Δa/a for the stoichiometric ErBaCo4O7 sample annealed in vacuum exhibits no anomalies in the course of a structural transition, whereas the parameters b and c undergo stepwise changes of oppositesigns. The different values of these changes Δb/b ≈ 4 × 10−3 and Δc/c ≈ −5 × 10−3 result in the stepwise volume change ΔV/V ≈ −10−3. A slight deviation from the oxygen stoichiometry affects the character of the structural distortion; namely, the magnitude of the anisotropic strain and the sign of the isotropic strain change. The structural distortion in the stoichiometric sample is accompanied by a sharp stepwise change in the Young’s modulus ΔE(T)/E0 ∼ 8 × 10–2, whereas the magnitude of elastic anomalies near TS in slightlynonstoichiometric samples with x ∼ 0.03 decreases by an order of magnitude. Comparison of elastic anomalies manifesting themselves near the magnetic phase transition temperature TN for distorted samples with different deviations from stoichiometry suggests that the arising long-range magnetic order in the cobalt subsystem is apparently affected not only by structural distortions but also by disorder introduced by nonstoichiometric oxygen.