Stabilization of over-stoichiometric Mn{sup 4+} in layered Na{sub 2/3}MnO{sub 2}

• Published in: Journal of solid state chemistry 2010-06, Vol.183 (6)
• Main Authors: Stoyanova, R., ICMCB-CNRS, Universite de Bordeaux, IPB-ENSCBP, 87 av. du Dr. A. Schweitzer, 33608 Pessac cedex, Carlier, D., Sendova-Vassileva, M., Yoncheva, M., Zhecheva, E., Nihtianova, D., Central Laboratory of Mineralogy and Crystallography, Bulgarian Academy of Sciences, Acad. G. Bonchev Str. bl. 107, 1113 Sofia, Delmas, C.
• Format: Article
• Language: English
• Subjects: ALKALI METAL COMPOUNDS; CARBON COMPOUNDS; CARBONATES; CHARGED PARTICLES; CHEMICAL ANALYSIS; COHERENT SCATTERING; COOLING; CRYSTAL DEFECTS; CRYSTAL LATTICES; CRYSTAL STRUCTURE; DIFFRACTION; ELECTRON MICROSCOPY; IONS; LASER SPECTROSCOPY; LAYERS; MAGNETIC PROPERTIES; MAGNETIC SUSCEPTIBILITY; MANGANATES; MANGANESE CARBONATES; MANGANESE COMPOUNDS; MANGANESE IONS; MATERIALS SCIENCE; MICROSCOPY; NMR SPECTRA; ORTHORHOMBIC LATTICES; OXYGEN COMPOUNDS; PHYSICAL PROPERTIES; POINT DEFECTS; QUENCHING; RAMAN SPECTROSCOPY; SCATTERING; SODIUM CARBONATES; SODIUM COMPOUNDS; SPECTRA; SPECTROSCOPY; STABILIZATION; STOICHIOMETRY; TEMPERATURE RANGE; TEMPERATURE RANGE 1000-4000 K; TRANSITION ELEMENT COMPOUNDS; TRANSMISSION ELECTRON MICROSCOPY; VACANCIES; X-RAY DIFFRACTION
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2010.04.024

Sodium manganates with nominal composition Na{sub 2/3}MnO{sub 2} were prepared by solid state reaction between Na{sub 2}CO{sub 3} and MnCO{sub 3} at 1000 {sup o}C. The composition and structure of Na{sub x}MnO{sub 2} were controlled by the rate of cooling from the temperature of preparation. This is a consequence of the capability of Na{sub 2/3}MnO{sub 2} to accommodate over-stoichiometric Mn{sup 4+} ions up to 12.5%. Structural characterization was carried out by XRD powder diffractions, TEM analysis and Raman spectroscopy. The composition and oxidation state of manganese were determined by chemical analysis and magnetic susceptibility measurements. The manganese distribution in the layers was analysed using electron paramagnetic resonance (EPR) spectroscopy. By quenching from 1000 {sup o}C, the orthorhombic distorted modification is stabilized. A phase separation into orthorhombic and hexagonal modifications takes place when Na{sub 2/3}MnO{sub 2} is slow cooled. The structure changes are concomitant with an increase in the oxidation state of Mn. The over-stoichiometric Mn{sup 4+} ions are accommodated in the hexagonal modification by creation of vacancies in the MnO{sub 2}-layers. - Graphical abstract: The composition and structure of Na{sub 2/3}MnO{sub 2} were controlled by the rate of cooling from the temperature of preparation. By quenching from 1000 {sup o}C, the orthorhombic distorted modification is stabilized. A phase separation into orthorhombic and hexagonal modifications takes place when Na{sub 2/3}MnO{sub 2} is slow cooled. The over-stoichiometric Mn{sup 4+} ions are accommodated in the hexagonal modification by creation of vacancies in the MnO{sub 2}-layers.