Microstructures and electrical properties of Mn/Co/Ni-doped BaBiO3 perovskite-type NTC ceramic systems

Mn/Co/Ni-modified BaBiO 3 -based negative temperature coefficient (NTC) ceramics with the formula, x [(3- y - z )Mn/ y Co/ z Ni-ions]+(1− x )BaBiO 3 ( x = 0.0–0.4, y = 0.96 and z = 0.48), were synthesized using a conventional solid state reaction. The effects of Mn/Co/Ni-substitute content on the phase structures and composition, microstructures and electrical properties were characterized by X-ray diffraction (XRD), scanning electron microscope and resistance–temperature measurements, respectively. XRD pattern analysis results revealed that the compound phases consisted of a main monoclinal BaBiO 3 phase and a secondary phase of Ba(Mn, Co, Ni)O 3 solid-solution with a hexagonal structure, which were detected at x = 0.05–0.2. In addition, according to the XRD patterns, the main phase changed from BaBiO 3 to a rhombohedral Bi 8.11 Ba 0.89 O 13.05 phase at x = 0.3, and this phase content increased dramatically as the x value increased to 0.4. For the related electrical properties, all of the samples demonstrated the typical characteristics of NTC thermistors across a relatively wide range of temperatures. The values obtained for B constant ( B 25/85 ) and the room-temperature resistivity ( ρ 25 ) were in the range of 2297–5235 K and 760 Ω cm −1 , 620 kΩ cm, respectively, which implied that the electrical properties of the present ceramic systems could be optimized via various substitutions in the Mn/Co/Ni-ions content. The variable values of ρ 25 were affected strongly by the changes in crystal structure and the decrease in charge carrier concentration. These composite ceramic materials are suitable candidates for a variety of NTC thermistor applications due to their widely adjustable electrical properties.