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Oxygen storage properties of hexagonal HoMnO3+δ
Konrad Swierczek1, Alicja Klimkowicz2, Kengo Nishihara2
1AGH University of Science and Technology, Faculty of Energy and Fuels, Department of Hydrogen Energy, al. A. Mickiewicza 30, 30-059 Krakow, Poland and AGH Centre of Energy, AGH University of Science and Technology, ul. Czarnowiejska 36, 30-054 Krakow, Poland.
Physical Chemistry Chemical Physics : PCCP
|July 14, 2017
Summary
This study investigates hexagonal HoMnO3+δ manganite
Area of Science:
- Materials Science
- Solid-State Chemistry
- Oxide Materials
Background:
- Hexagonal manganites (RMnO3) are promising materials for various applications.
- Understanding their structural and oxygen content changes is crucial for optimizing performance.
- HoMnO3+δ exhibits a phase transition between stoichiometric (Hex0) and oxygen-loaded (Hex1) phases.
Purpose of the Study:
- To investigate the structural and oxygen content changes of hexagonal HoMnO3+δ manganite.
- To study the oxygen storage properties during phase transitions.
- To determine the kinetics and transition temperatures of oxygen incorporation and release.
Main Methods:
- In situ X-ray diffraction (XRD) and thermogravimetry (TG).
- Oxidation and reduction processes at elevated temperatures in oxygen and air.
- Solid-state synthesis and high-impact mechanical milling.
- X-ray absorption spectroscopy (XAS) for Mn valence and magnetic susceptibility measurements.
Main Results:
- The Hex0 → Hex1 phase transition (δ = 0 to δ ≈ 0.28) is limited by surface reaction and nucleation.
- Transition temperatures are 290 °C (heating) and 250 °C (cooling) at 0.1° min⁻¹.
- Ball-milling enhances oxygen incorporation in air (220-255 °C) after prolonged heating.
- Mn valence determined by XAS aligns with TG results.
Conclusions:
- The phase transition kinetics in HoMnO3+δ are influenced by synthesis method and annealing conditions.
- Lanthanide ionic size significantly impacts redox properties in hexagonal manganites.
- Optimizing (Y,Ln)MnO3+δ synthesis with larger ionic radii could improve practical properties.
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