Structure and electrical properties of single-phase cobalt manganese oxide spinels Mn{sub 3-x}Co{sub x}O{sub 4} sintered classically and by spark plasma sintering (SPS)

• Published in: Journal of solid state chemistry Vol. 182; no. 2
• Main Authors: Bordeneuve, Helene, Guillemet-Fritsch, Sophie, Rousset, Abel, Schuurman, Sophie, Poulain, Veronique
• Format: Journal Article
• Language: English
• Published: United States 15-02-2009
• Subjects: CERAMICS; COBALT COMPOUNDS; ELECTRICAL PROPERTIES; HEAT TREATMENTS; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; MANGANESE IONS; MANGANESE OXIDES; OXALATES; PHASE DIAGRAMS; POLARONS; PYROLYSIS; SEMICONDUCTOR MATERIALS; SINTERING; SOLID SOLUTIONS; SPINELS; TEMPERATURE COEFFICIENT; THERMISTORS
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2008.11.004

Cobalt manganese oxide spinels Mn{sub 3-x}Co{sub x}O{sub 4} (with 0.98{<=}x{<=}3) were prepared by the thermal decomposition in air of oxalate precursors. The influence of the thermal treatments on the structure of these materials is emphasized. Single-phase ceramics were obtained after optimization of the sintering parameters. A precise phase diagram for the Co-Mn-O system is proposed according to thermal stability and structure of oxide powders. The electrical measurements on single-phase ceramics show that low values of resistivity can be achieved. The conduction could take place through jumps of polarons between Mn{sup 3+} and Mn{sup 4+} on octahedral sites. These compounds present interesting electrical characteristics for negative temperature coefficient (NTC) thermistor applications. - Grapical abstract: After elaboration of single-phase and well densified ceramics Mn{sub 3-x}Co{sub x}O{sub 4} (with 0.98{<=}x{<=}3) by conventional and spark plasma sintering, electrical measurements have been taken and low values of resistivity can be achieved. The conductivity shifts from an insulator, Mn{sub 3}O{sub 4} (cationic distribution: Mn{sup 2+}[Mn{sup 3+}]{sub 2}O{sub 4}) to a semiconductor solid solution probably due to the hopping of polarons between Mn{sup 3+} and Mn{sup 4+} on octahedral sites.