ZIRCONIUM OXIDE-COMPOSITED Fe_(0.5)Mn_(1.84)Ni_(0.66)O_4 NEGATIVE TEMPERATURE COEFFICIENT THERMISTOR CERAMICS

Negative temperature coefficient(NTC) thermistors of Fe0.5Mn1.84Ni0.66O4 with spinel structure,composited with zirco-nium oxide(ZrO2),were prepared by the Pechini method.The phase composition and microstructure were characterized using X-ray diffraction and scanning electron microscope,and the electric properties were also measured.The experimental results show that much ZrO2 with monoclinic structure was homogeneously dispersed in the spinel grain boundary,but only a little ZrO2 could occupy the lattice in the spinel.With increasing ZrO2 content,the B value,the thermal constant(unit in Kelvin),had a little increase and then stayed constant,whereas,the resistivity had a tendency to keep increasing.Zirconium oxide could restrain the aging.The possible mechanism is that ZrO2 particles well-dispersed in the spinel grain boundary have a pinning effect on the spinel cation vacancies,which restricts the motion of cation vacancies.