Peculiar Properties of Electrochemically Oxidized SmBaCo2−xMnxO5+δ (x = 0; 0.5 and 1) A-Site Ordered Perovskites

Anna Olszewska,Konrad Świerczek,Anna Niemczyk

doi:10.3390/cryst10030205

Abstract

Fully-stoichiometric SmBaCo2-xMnxO6 oxides (x = 0, 0.5, 1) were obtained through the electrochemical oxidation method performed in 1 M KOH solution from starting materials having close to equilibrium oxygen content. Cycling voltammetry scans allow us to recognize the voltage range (0.3–0.55 V vs. Hg/HgO electrode) for which electrochemical oxidation occurs with high efficiency. In a similarly performed galvanostatic experiment, the value of the stabilized voltage recorded during the oxidation increased with higher Mn content, which seems to relate to the electronic structure of the compounds. Results of the iodometric titration and thermogravimetric analysis prove that the proposed technique allows for an increase in the oxygen content in SmBaCo2-xMnxO5+δ materials to values close to 6 (δ ≈ 1). While the expected significant enhancement of the total conductivity was observed for the oxidized samples, surprisingly, their crystal structure only underwent slight modification. This can be interpreted as due to the unique nature of the oxygen intercalation process at room temperature.

Highlights

Nonstoichiometry is well-known to impact the physicochemical properties of ceramic materials, since its change may cause modifications in the crystal structure, and influences the magnetic and transport properties, often having a direct impact on the applicability of particular compounds [1,2,3]
Its analysis allows for the three main regions corresponding to the following processes to be distinguished [7]: (I) The formation of a double layer on the working electrode/electrolyte interface; (II) the actual electrochemical oxidation, covering ca. 0.3–0.55 V
SmBaCo2−x Mnx O5+δ (x = 0; 0.5 and 1) oxides were successfully synthesized using the sol-gel route combined with high-temperature annealing, performed in air or argon atmospheres

Summary

Introduction

Nonstoichiometry is well-known to impact the physicochemical properties of ceramic materials, since its change may cause modifications in the crystal structure, and influences the magnetic and transport properties, often having a direct impact on the applicability of particular compounds [1,2,3]. An effective oxygen incorporation into/release from the crystal structure may be carried out only if sufficiently high mobility of the oxygen anions is ensured. This can be achieved if high temperatures—above 300 ◦ C, but typically starting from ca. While Co4+ /Co3+ couples existed only for SmBaCo2 O5+δ , the presence of the more stable Mn4+ ions reduced the concentration of the highly-charged Co4+ In this range of concentrations (x), the increased manganese content negatively affected the electrical conductivity by changing the amount of the more effectively conducting species [32]. For more detailed information regarding the impact of Mn content on the conductivity mechanism in the REBaCo2−x Mnx O5+δ system, please see [14,15,17]

Methods

Results

Conclusion