Investigation Of Doping Modification And Electrical Properties Of NiO-based Thermosensitive Ceramics

Negative temperature coefficient（NTC）thermistors,as the most commonly used thermal device in temperature sensors,has the characteristics of high temperature sensitivity,fast response,good thermal stability and wide applicable temperature range.They are widely used in industrial production,household appliances,biomedical,aerospace and military industries and so on.With the development of electronic information technology and measurement/control technology towards diversification and high precision,design and preparation of NTC thermistors with adjustable room temperature resistivity(ρ₂₅),high thermal sensitivity and electrical stability are very practical topic.In this thesis,single cation oxide of NiO was used as the research object.NTC thermistors with superior performance were prepared by elemental doping and composite modification.The phase composition,microstructure,electrical properties and aging stability of the prepared ceramics were investigated.The relevant microscopic mechanisms are analyzed.The main research contents and results are as follows:（1）Rare earth elements（Y,Sm and La）doped NiO-based ceramics,Ni_1-xY_xO（xNYO,0≤x≤0.03）,Ni_1-ySm_yO（yNSO,0.01≤y≤0.12）,Ni_1-zLa_zO（zNLO,0.005≤z≤0.12）,were prepared by solid-state reaction method.The prepared ceramics contain Y₂O₃,Sm₂O₃,La₂NiO₄ trace impurity phases in addition to NiO main phase with rock-salt cubic structure.All doped NiO-based ceramics show typical NTC feature,and show wide adjustableρ₂₅ and material constant(B_25/85).The adjustable ranges ofρ₂₅ of,xNYO,yNSO and zNLO ceramics are 1143-19188Ω·cm,664-2453Ω·cm and 3.6-652.3Ω·cm,respecivlly,and the related B_25/85 values range in 5296-6025 K,5200-5280 K and 1343-5254 K,respectively.Analysis of electrochemical impedance spectra（EIS）reveals that the NTC effect of xNYO and yNSO ceramics is a combination of grain effect and grain boundary effect.The doping of Y³⁺and Sm³⁺ions significantly reduces the grain resistance and grain boundary resistance of the ceramics.（2）Y³⁺/Ti⁴⁺and Sm³⁺/Ti⁴⁺co-doped NiO-based ceramics were prepared by solid-state reaction method,respectively.Ni_0.99-mY_0.01Ti_mO（mNYTO,0.003≤m≤0.03）ceramics contain main phase of rock-salt cubic NiO and Y₂Ti₂O₇ impurity phase with cubic pyrochlore structure Y₂Ti₂O₇;Ni_0.99-nSm_0.01Ti_nO（nNSTO,0.005≤n≤0.02）ceramics are composed of rock-salt cubic NiO phase and orthorhombic perovskite-type SmTiO₃ phase or cubic pyrochlore-type Sm₂Ti₂O₇ phase.All ceramics exhibit obvious NTC effect and have high B_25/85 values and widely adjustableρ₂₅.Theρ₂₅ ranges are 7901-48313Ω·cm for m NYTO and1067-69479Ω·cm for nNSTO,and B_25/85ranges are 5922-7079 K for mNYTO and 5254-6478 K for nNSTO.EIS analysis revealed that the grain conduction is consisted of models of band conduction and polaron hopping conduction,whose contribution are different in different temperature regions.The conduction model for grain boundary effect is proposed to be thermally activated crossing the grain boundary barrier of charge carriers.（3）BiSbO₃ modified Ni_0.99Y_0.01O-α%BiSbO₃（0.01NYO-αBSO,1≤α≤6,weight percent）composite ceramics were prepared by solid-state reaction method.The phase of 0.01NYO-αBSO ceramics is composed of NiO main phase and Y₂O₃ and（Bi,Sb,Y）₂O₄ secondary phases.The prepared composite ceramics have good NTC properties,and theirρ₂₅ and B_25/85 increase from 1403 to 14076Ω·cm and from 5207 to 5829 K,respectively,with the increase of BSO content.The introduction of BSO can effectively improve the aging stability of xNYO ceramics.After being aging treated in air at 150℃ for 800 h,the resistance drift rates of reduced from-5.8%（0.01NYO）to 0.21%（0.01NYO-2BSO）.The aging characteristic was discussed basing on the redox of adsorbed water at sureface/interface of ceramics.