Study On The Properties Of Sno₂ Ceramics Doped Ceo₂, La₂o₃

SnO₂ is an obvious semiconductor with wide band gap,which bandwidth is in the range of 3.6～4.0eV.The main carrier is free electron in crystal lattice.Pure tin oxide is difficult to use as conductive ceramic,but it could become a good electrical conductors after other elements were doped.Tin dioxide has been widely used as gas sensor,thermistor,varistors,as well as films.However,only one aspect of the electrical or sintering properties was studied. SnO₂ has the good performance of enduring high temperature,corrode-resistance, good conductance at high temperature,so it was used as electrode in electric melting furnace for all kinds of glass.As an electrode,Whereas,SnO₂ must have good electrical properties to meet the special circumstance and performance requirements in the glass melting process,as well as sintering properties and mechanical properties.In this paper,the traditional process was introduced to prepare SnO₂ ceramics, rare earth oxides were doped in order to improve the performance.The crystal of SnO₂ ceramics was analysed by XRD;the morphology was observed by SEM;and the ingredient was inspected by EDS.Density is tested according to Archimedes' principle.Furthermore,the resistivity at room temperature and the relation between resistivity and temperature were also analyzed.Firstly,through the orthogonal experiments,it was studied the influence on electronic resistivity at normal temperature and density by doping CeO₂,Sb₂O₃, MnO₂,the ZnO to the SnO₂ in three levels(0.25wt%,0.50wt%,1.00wt%).Results shew that Sb₂O₃ could induce the resistivity to reduce obviously,and MnO₂ & ZnO have little effects on the resistivity and density of SnO₂ ceramics.However,the electronic resistivity of SnO₂ ceramics with 1.00wt%CeO₂ increased 1.6 times higher than that without CeO₂,and the SnO₂ ceramic density improved to 95.8%of theoretical density.Through the analysis of XRD and the SEM,results showed the SnO₂ crystal tended to grow integrally with the increase of doping content of CeO₂, simultaneously the density improved.Moreover,when more CeO₂ were doped,the inner oxygen vacancy,the free electron and other current carriers were reduced,which would cause the resistivity at normal temperature of SnO₂ ceramics elevated obviously.Secondly,the influence of the SnO₂ ceramics doping La₂O₃ on resistivity and the microstructure was studied.The results showed La₂O₃ could promote the growth of SnO₂ crystal,and decreased clearly the resistivity in certain doping scope.When doping content of the La₂O₃ is by 0.50wt%,the second phase was found by SEM, which was confirmed to be La₂Sn₂O₇ by XRD and EDS.The new second phase could increase the confusion of the ions' arrangement,and enhance density of the vacancy in the structure.Therefore the resistivity of the SnO₂ ceramics reduced considerably, and the lowest electronic resistivity is by 3340cm,only as 15%without La₂O₃.When La₂O₃ was doped by 1.00wt%,the second phase La₂Sn₂O₇ decreased clearly and the resistivity of samples increased again.Thirdly,the density and the mechanical properties of SnO₂ ceramics with La₂O₃ were studied.The density of samples with 0.50wt%La₂O₃ doped reached 6.53g/cm³, as well as the hardness and toughness increased by 14.13%and 8.3%respectively. The second phase La₂Sn₂O₇,distributed over the SnO₂ crystal boundary or the phase boundary would come into being the stress,whereas,the kind of stress in the SnO₂ crystal enhanced the toughness of SnO₂ ceramics.Finally,the feasibility of the SnO₂ ceramics used as the industry electrode to get magnesium through the inner heating method was discussed.