Sno < Sub > 2 < / Sub > Base Negative Temperature Coefficient Of Thermal Ceramic Structure And Performance Study

Negative Temperature Coefficient Thermistors are widely used in various industrial and domestic applications, such as elements for suppression of in-rush current, for temperature measurement and control, and for the compensation of other circuit elements. Most of the NTC ceramics are the 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. However, the applications of NTC thermistors based on the spinel oxides are commonly limited to narrow temperature range for the relaxation of the crystal structure at high temperature. To prepare a novel NTC material, the Sb and P co-doped SnO2ceramics were studied in this thesis. The research work includes the following aspects.(1) Sn1-xSbxO2-δ (x=0.3%,0.5%,0.7%,1%) powders were prepared by a wet chemical process using Sn powders as raw materials and the related ceramics were obtained by the conventional sintering technique. The p50℃of Sn1-xSbxO2-δ ceramics decreases with increase of Sb concentration changing within the range of102～106Ω·cm. The material constants B are changing within the range of2000～5000K. The ceramics have a tetragonal crystal structure from the XRD spectrum. Morphological study on the samples using SEM showed dense crystalline structure, well-developed grains and grain boundaries.(2) Impedance analysis was employed to study the contribution of grain and/or grain boundary to the NTC effect of the Sn1-xSbxO2-δ ceramics. It is found that the conduction in these ceramics is dominated by the grain boundary.(3) Two kinds of sintering additives (Li-Ti-O and CuO) were selected to study the influence of the sinter-ability and properties of the Sb and P co-doped SnO2ceramics. The ceramics with sintering additives have higher densities (>95%) sintered at low temperatures1100～1200℃. With the increase of the sintering additives, the resistance of the ceramics increased as well. So the quantity of the sintering additives (Li-Ti-O and CuO) is limited to1wt%and2wt%respectively to keep well electrical properties.(4) The influence of Sb and P doping on the NTC properties of SnO2based ceramics was studied. It is found the resistivity and material constants B can be adjusted by dopants. The conduction in these ceramics is proposed to be dominated by both grain and grain boundary.