RuO2 doping and its influence on phase structure, cations state, and electrical properties of Mn1·6Co0·4CuO4 ceramics

Abstract RuO2 is a typical metal conductor with low resistivity and is available in a wide range of electronic components to decrease resistance and temperature resistance coefficient. Mn–Cu–Cu–O compounds with different RuO2 dopping contents were prepared with RuO2 and other oxide powders via a solid-state reaction method. The X-ray diffraction patterns of the compounds revealed a primarily spinel-structure, moreover, as the Ru content increased, diffraction spectrum for other impurities appeared. Images of Mn–Cu–Cu–Ru (MCCR) ceramics showed significant differences in grain size. The energy-dispersive X-ray spectroscopy mapping results revealed a non-homogenous element distribution. The valence states of metal elements were investigated using X-ray photon spectroscopy, which demonstrated conversion of the valence state in Cu (Cu2+ to Cu+) and Mn (Mn2+ to Mn3+ and Mn4+) cations, whereas Co may have a single valence state, Co2+. With increasing RuO2 content from 0 to 0.3, the resistivity of the material decreased to 7.43 and 0.13 Ω cm, whereas the activation energy were 0.205, 0.147, 0.132, and 0.115 eV, while the thermal sensitivity (B) constant of the materials were 2378, 170, 153, and 1329 K, respectively. These results can be used to design a negative temperature coefficient (NTC) thermistor with low resistance and B value.