Influences Of Nitride Dopants On Microstructure And Electrical Properties Of ZnO Varistor Ceramics

ZnO based varisitors have been widely used as surge absorb devices in electrical systems due to their excellent nonlinear current-voltage?I-V?characteristics and large surge-current withstanding capability.It is meaningful to study the effect of dopants on ZnO varistor ceramics'microstructure and electrical performances,especially the properties under high current region.In this paper,ZnO based varistor ceramics doped with different nitride addtives were fabricated via solid state method.The phase composition,microstructure,dielectric spectroscopy,and electrical performances both in low current region and large impulse current region were investigated.The influences of C₃N₄ additives on the microstructure and electrical properties of ZnO varistor ceramics were investigated.According to the double Schottky barrier model,N^3-enter the lattice site of O^2-and provide extra holes,which reduces the donor concentration and increases the barrier height.The nonlinearity and surge current withstanding capability were improved,also.Experimental results showed that grain growth was restrained and breakdown voltage gradient was improved with the doping of C₃N₄.Samples doped with different amount of C₃N₄ were sintered to be similar in breakdown voltage gradient,and submitted to surge current test.Results showed that the residual voltage ratio of C₃N₄-added samples are lower than C₃N₄-free samples.The results of dielectric spectroscopy showed that terminal capacitance decreases with the increase of C₃N₄ content,which indicated that the barrier height was improved.Thus,the nonlinearity in high current region and surge current withstanding capability of C₃N₄-added samples were improved.The influences of BN doping on ZnO varistor ceramics were studied.B₂O₃-doping could promote the grain growth of ZnO and decrease the sintering temperature due to the low melting temperature of Bi₂O₃-B₂O₃ glass.However,adding amount of B₂O₃ was limited,because boric acid,which produced from the reaction of B₂O₃ and H₂O during the ball mill process,would forming complexing agent with PVA.Dopiong BN instead of B₂O₃ is able to solve the problem.Thermogravimetric?TG?and differential scanning calorimetric?DSC?analyses were used to analyse the suitable sintering temperature of BN-doped varistor ceramics.And the influences of BN doping on the microstructure and electrical properties of ZnO varistor ceramics were studied.