Preparation and characterization of Fe3+-doped Ni0.9Co0.8Mn1.3−xFexO4 (0 ≤ x ≤ 0.7) negative temperature coefficient ceramic materials

Based on spinel-type semiconducting electroceramics, negative temperature coefficient (NTC) thermistor materials, Ni0.9Co0.8Mn1.3−xFexO4 (0 ≤ x ≤ 0.7), with different compositions were synthesized by a co-precipitation method. The optimal pH value and the influence of Fe3+ doping during the synthesis processing were discussed. As-prepared Ni0.9Co0.8Mn1.3−xFexO4 materials were characterized by DT/TGA, XRD, FTIR, SEM, electrical measurement and impendance analysis. It was found that, as the Fe doping content in the Ni0.9Co0.8Mn1.3−xFexO4 samples increased, both the grain size and the density decreased. The as-sintered Ni0.9Co0.8Mn1.3−xFexO4 samples presented a single-phase cubic spinel structure. The impendance diagram indicated that the grain boundary resistance was dominant in the overall impendance of Ni0.9Co0.8Mn1.3−xFexO4 NTC ceramic materials. The value of ρ25, B25/50, slope and activation energy for the samples Ni0.9Co0.8Mn1.3−xFexO4 sintered at 1200 °C were in the range of 453.1–2411 Ω cm, 3103–3355 K, 3.27325–3.43149 and 0.28207–0.29325 eV, respectively. This suggests that the electrical properties can be adjusted to desired values by controlling the Fe3+ ion doping content.

Graphical abstractRelationships between total concentrations of metal ions and pH value in Men+(Co2+, Mn2+, Ni2+, Fe3+)–CO32−–NH3–H2O by co-precipitation method.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► In this study the Fe3+ ion doped Ni–Co–Mn–O NTC quaternary materials are synthesized by a co-precipitation method. ► The electrical properties of the NTC thermistors can be controlled by changing the Fe ion contents. ► The impedance of Ni–Co–Mn–O NTC materials exhibited irregular semicircle. ► Therefore, the electrical properties can be adjusted to desire values depending on the Fe3+ ion doped.