Structure and electrical properties of single-phase cobalt manganese oxide spinels Mn3−xCoxO4 sintered classically and by spark plasma sintering (SPS)

Cobalt manganese oxide spinels Mn3−xCoxO4 (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 Mn3+ and Mn4+ on octahedral sites. These compounds present interesting electrical characteristics for negative temperature coefficient (NTC) thermistor applications.

Grapical abstractAfter elaboration of single-phase and well densified ceramics Mn3−xCoxO4 (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, Mn3O4 (cationic distribution: Mn2+[Mn3+]2O4) to a semiconductor solid solution probably due to the hopping of polarons between Mn3+ and Mn4+ on octahedral sites.Figure optionsDownload as PowerPoint slide