Prepare And Study Of Sr-system PTC Materials Of Low-temperature Sintering

(Ba,Sr)TiO₃ is the main material for preparing high dielectric constant series ferroelectric components, widely applied to electronic ceramics fabrication area, especially to fabricate low Curie point PTC (Positive Temperature Coefficient) component mainly utilized in demagnetizing and overcurrent protection. However, the sintering temperature of low Curie point (Ba,Sr)TiO₃ ceramic by conventional solid phase method reaches up to 1350℃. If sintering temperature could be decreased and materials consumption be reduced, life time of sintering equipment can be extended. In order to decrease the sintering temperature of (Ba,Sr)TiO₃,different amounts of PbO and BN were added into in the preparation process of low Curie point (Ba,Sr)TiO₃ by secondary adding method. The solid state reaction was used to fabricate samples with PbO and BN as mineralizing agent, which is because that the process and adding style can improve properties of the material and decrease the sintering temperature obviously.The microstructure tissues and properties were tested and characterized by X-ray diffractometer (XRD),scanning electron microscope (SEM),resistance-temperature characteristic tester (R-T), voltage-ampere characteristic tester, and so on.As for properties of PTC ceramics, the key factor is sintering temperature except formula. The influence of process conditions on PTC properties of samples was major analyzed and discussed, mainly the influence of sintering temperature, in results and discussion. At the same time, the influence of differentζ(PbO: BN) on properties of Sr series PTC materials under the condition of low temperature sintering was also discussed and researched. The main study results are listed as follows:(1) Keeping the amount of BN as constant, adding PbO can decrease room temperature resistivity of the materials. (2) Adding PbO can increase the amount of BN, which is favor for reducing sintering temperature.(3) BN is an effective sintering mineralizer. PbO and BN can generate liquid phase at 900℃and promote sintering, thus it decreasing sintering temperature for about 168℃. Adding PbO is beneficial to decreaseρ₂₅ and improving PTC effect of samples.(4) When the mass ratio of PbO to BN (PbO: BN) equals 4:3, the samples sintered at 1182℃holding for 2 hours have semiconductivity with distinct properties using BN as sintering agent, Mn²⁺ as acceptor impurity (adding into form of Mn(NO₃)₂ solution), and Y³⁺ as donor impurity (Y₂O₃). The sample has the following properties: T_c: 64.9℃, R₂₅: 125?,α_10/25: 10.54%℃^-1,ρ_max/ρ_min: 2.553×10⁵ and V_b: 696.7V, which has high practical value.