Electrical properties of Ni-Mn-Co-(Fe) oxide thick-film NTC thermistors prepared by screen printing

Ni-Mn-Co-(Fe) oxide thick films were coated on an alumina substrate by a screen-printing technique. The electrical properties of the thick films, as a function of composition and sintering temperature, were investigated. All the thick-film negative temperature coefficient (NTC) thermistors prepared showed a linear relationship between log resistivity and the reciprocal of the absolute temperature, indicative of NTC characteristics. As the amount of Mn3O4 in (Ni2-xMnxCo1.0)O-4 (0.6 less than or equal to x less than or equal to 1.8) thermistors increased, the resistivity and the coefficient of temperature sensitivity decreased to a minimum value and then increased again. Also, at a given Ni-Mn oxide content, the resistivity and the coefficient of temperature sensitivity for (Ni1.0Mn1.0Co1-xFex)O-4 (0.25 less than or equal to x less than or equal to 1.0) and (Ni0.75Mn1.25Co1-xFex)O-4 (0.25 less than or equal to x less than or equal to 0.75) thermistors increased with increasing Fe2O3 content. The influence of composition and sintering temperature on the electrical properties of the thermistors is discussed. (C) 2003 Kluwer Academic Publishers.