Oxygen non-stoichiometry in Ru-1212 and Ru-1222 magnetosuperconductors

TL;DR

This study investigates the oxygen non-stoichiometry in Ru-1212 and Ru-1222 magnetosuperconductors using thermogravimetric analysis, revealing differences in oxygen content and Ru valence states influenced by annealing conditions.

Contribution

It provides detailed thermogravimetric and spectroscopic analysis of oxygen content and Ru valence in Ru-1212 and Ru-1222, highlighting their distinct oxygen stoichiometry behaviors.

Findings

Ru-1222 exhibits wider oxygen-content tuning than Ru-1212.

Oxygen release occurs around 300 and 450°C during reduction.

Ru-1212 is nearly stoichiometric after O2 annealing, Ru-1222 remains oxygen deficient.

Abstract

Here we report the results of thermogravimetric (TG) analysis on the oxygen non-stoichiometry of RuSr2GdCu2O8 (Ru-1212) and RuSr2(Gd0.75Ce0.25)2Cu2O10(Ru-1222) samples. With TG annealings carried out in O2 and Ar atmospheres it was found that the oxygen content in Ru-1212 remains less affected upon various annealings, while for Ru-1222 wider-range oxygen-content tuning is possible. When heated in H2/Ar atmosphere the both phases release oxygen upon breaking down to mixtures of metals (Ru and Cu) and binary oxides (CeO2, Gd2O3, and SrO) in two distinct steps around 300 and 450 oC. This reductive decomposition reaction carried out in a thermobalance was utilized in precise oxygen content determination for these phases. It was found that the 100-atm O2-annealed Ru-1212 sample was nearly stoichiometric, while the similarly treated Ru-1222 sample was clearly oxygen deficient. X-ray absorption near-edge (XANES) spectroscopy was applied to estimate the valence of Ru in the samples. In spite of the fact that the Ru-1212 phase was shown to possess less oxygen-deficient RuO2 layer, the valence of Ru as probed with XANES was found to be lower in Ru-1212 than that in Ru-1222.