Aging Behaviour in Ni0.5Cox Mn-2.5_O-x(4) (x=0.5, 0.8 and 1.1) Thermistors

Negative temperature coefficient (NTC) thermistors are required to have good electrical stability for many domestic and industrial applications. The aging phenomenon of NTC thermistors can be described as the change in electrical resistance due to thermal stress with time. In this study, Ni0.5Co Mn-2.5_O-x(4) (x = 0.5, 0.8 and 1.1) ceramics were fabricated by the conventional solid-state reaction method. The powder mixtures of manganese, cobalt and nickel oxides were ball-milled for 5 h. The powders were calcinated at 900 degrees C for 2 h. The samples were sintered at 1100 degrees C for 5 h. To investigate the aging behaviour, the samples were held at 150 degrees C for 400 h. Aging in the samples were calculated by the following equation; AR/R0 = (R - R-0)/R-0 in which Ro is the resistance at 25 degrees C before the aging test, and R is the resistance at 25 degrees C after the aging test.