Ni/co Doping Batio < Sub > 3 < / Sub > Base Ceramic Structure And Electrical Properties

Negative temperature coefficient (NTC) thermistors refer to the materials whose resistivity decreases with the increasing temperature. NTC ceramic materials are widely used in various applications, such as elements and/or devices for suppression of in-rush current, components for temperature measurement and control, and elements for compensation of other circuit elements. Most NTC ceramic materials are solid solutions of transition metal oxides with spinel structure, such as Mn-Ni-O, Mn-Ni-Co-O, Mn-Ni-Cu-0and Mn-Ni-Fe-O etc.. Since the electrical properties and the distribution of cations are closely related to the microstructures of grain or grain boundary, spinel NTC ceramics are easy to deteriorate.In this study, BaTiO3-based ceramic materials were prepared to investigate the influence of Co-doping and Ni-doping on crystal structures and properties. The research finds that the Co-doped and Ni-doped BaTiO3-based ceramics have hexagonal perovskite structure (h-BaTiO3), and shows desirable NTC effects.BaTi1-x-yNixCoyO3-δ(x=0.05、0.1、0.15、0.2、0.3, y=0、0.05.0.08.0.1) powders were prepared by a wet chemical method and the related ceramics were obtained by the conventional sintering technique. The resistivity p of the ceramics decreases as the temperature increases. The materials show novel NTC effects, the related material constants (B) range from2900K to4700K. When y=0and x=0.1, the samples have h-BaTiO3structure. When x=0.2or0.3, the samples have the main phase of h-BaTiO3and few Ba2Ti04phase. When x=0.1, y=0.08or0.1, the samples have relatively stable electrical properties and obvious linear relationship. As the concentration of Co is increased, the electrical properties remained stable.Impedance analysis was employed to study the contribution of grain and/or grain boundary to the NTC effect. The results showed that the resistances of BaTi0.82Ni0.1Co0.0803-δ ceramic samples were mainly affected by grain effect. The NTC effect can be attributed to the electrons hopping between Co3+and Co2+.Three kinds of sintering additives (Li-P-O, Li-Si-O and Li2CO3) were selected to investigate the influence of the sintering abilities and electrical properties of BaTi0.82Ni0.1Co0.08O3-δceramics. The results indicated that the applied sintering additives can improve the ceramic sinter ability and reduce obviously the sintering temperatures about200～400℃, compact ceramic samples without the sacrifice of electrical properties can be obtained under a relatively low temperature (1100℃) when0.5wt%Li2CO3was used as the sintering additive.The influence of various elements (Na, K, La, Bi, Ce, Y and Nb) doping on electrical properties of BaTi0.82Ni0.1Co0.08O3-δ ceramics was studied. The results show that the doping did not affect the samples’ crystal structures and the samples still had evident NTC effects. Na-doping enhanced the sintering abilities. The density of Na-doped samples was increased and the porosity decreased. Meanwhile, the materials constant (B) and the activation energy (Ea) were increased to different degrees.