EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

It is documented in the literature that hexagonal rare earth manganites can reversibly incorporate significant amount of interstitial oxygen at temperatures in the range of 200-300 °C. Despite that normally the process occurs only in O2 atmosphere, proper manipulation of the composition can enable the materials to absorb oxygen even from air: as reported, even small substitution of Y with Pr (e.g. 5 mol.%) in Y0.95Pr0.05MnO3+δ improves its oxygen storage capacity from 0.4 to 2.5 wt.% in the same conditions of the thermal swing process. The oxygen incorporation is expected to significantly affect transport properties of the compounds, through the associated partial oxidation of Mn3+ to Mn4+.
In the presented study, two mixed ionic-electronic conductors, YMnO3+δ and Y0.95Pr0.05MnO3+δ, were investigated in terms of their transport properties in various atmospheres at elevated temperatures. Materials were synthesized via sol-gel auto combustion method, followed by high temperature (1000 °C) annealing in Ar. As-prepared powders were hexagonally structured (P63cm), as confirmed by X-ray diffractometry. Electrical conductivity of the sintered samples was examined by 4 probe DC method. Measurements were performed in synthetic air (ca. 20 vol.% of O2) and in Ar (cO2 ≤ 2 ppm), which together with thermogravimetric data allowed to establish the influence of the interstitial oxygen content on the total conductivity. It was found that for Y0.95Pr0.05MnO3+δ sample, value of the total conductivity increased significantly after gas change from Ar to air: e.g. from 10-6 to 10-3 at 250 °C. Seebeck coefficient measurements were conducted to evaluate dominating charge carrier. Moreover, conductivity was also studied in H2O-containing atmospheres in order to evaluate potential application of the oxides as mixed protonic-electronic conducting ceramics for low-temperature SOFC/PCFC electrodes.