Research On Transition Metal Oxide Doped LSGM Dense Diffusion Barrier Limiting Current Oxygen Sensor

Dense diffusion barrier limiting current oxygen sensors which can overcome the plugging and deformation of pore-based diffusion barrier limiting current oxygen sensors have many advantages of good stabilization,high sensitivity,fast response,long service life,low cost and so on,and has been proved to have a promising future.The La_0.8Sr_0.2Ga_0.8Mg_0.2O_3-??LSGM?solid electrolyte,and mixed conductor materials of La_0.8Sr_0.2(Ga_0.8Mg_0.2)_1-xCr_xO_3-??LSGMCr?,La_0.8Sr_0.2(Ga_0.8Mg_0.2)_1-xFe_xO_3-a?LSGMFe?,La_0.8Sr_0.2(Ga_0.8Mg_0.2)_1-xCo_xO_3-??LSGMCo?and La_0.8Sr_0.2Ga_1-xCo_xO_3-??LSGCo??x=0.1-0.9?were prepared by a solid-state reaction method,respectively,and the crystal structure,thermal expansion properties,electrical conductivity,chemical compatibility and micro-morphology were characterized.The results showed that:?1?The crystal structures of LSGM,LSGMCr,LSGMFe,LSGMCo and LSGCo were all perovskite,and the crystal structures of LSGMFe,LSGMCo and LSGCo were transformed with increasing of x.?2?The thermal expansion coefficient?TEC?of LSGM in the temperature range of 300-1000 ? was 12.51 ×10-6K-1,which were similar with the LSGMCr?x=0.7?and the LSGMFe?x=0.9?;while the TECs of LSGMCo and LSGCo were large different from that of LSGM.?3?The conductivity of LSGMCr,LSGMFe,LSGMCo and LSGCo increased with increasing of x and temperature,and a transition from semiconductive conduction to metallic conduction was observed with increasing of temperature for LSGMFe,LSGMCo and LSGCo.LSGMCr?x=0.7?and LSGMFe?x=0.9?were selected as dense diffusion barriers based on the TECs similarity to LSGM,and the oxygen sensors with LSGMCr?x=0.7?and LSGMFe?x=0.9?dense diffusion barrier and LSGM solid electrolyte were prepared by the Pt sintered-paste as well as co-pressed and co-sintered methods,respectively.In addition,the oxygen sensors with LSGM solid electrolyte as matrix were prepared by co-diffusion method.The influences of temperature,oxygen content and the thickness of dense diffusion barrier?L?on sensing performance of oxygen sensors were investigated.The results showed that:?1?The limiting current oxygen sensors with LSGMCr?x=0.7?and LSGMFe?x=0.9?dense diffusion barrier prepared by the Pt sintered-paste as well as co-pressed and co-sintered methods exhibited excellent limiting current plateaus in a wide range of oxygen content and temperature.The limiting currents?IL?of the oxygen sensors depended well linearly on the oxygen contents,and logIL depended well linearly on 1000/T?temperature?.The IL decreased with increasing of L value.The polarization resistance of the sensor decreased with increasing of temperature and oxygen content.?2?The limiting current oxygen sensors with LSGMCr and LSGMFe dense diffusion barrier prepared by co-diffusion method exhibited excellent limiting current plateaus in the temperature range of 700-850 ? and 800-850 ?,while in the oxygen content range of 0.4 mol%-8.4 mol%and 0.1 mol%-4.9 mol%,respectively.IL depended well linearly on the oxygen contents,and logIL depended well linearly on 1000/T.The polarization resistance of the sensor decreased with increasing temperature.SEM-EDS analysis showed that LSGMCr and LSGMFe dense diffusion barrier prepared by the co-diffusion method with about 50 ?m and 40 ?m thicknesses were well attached to the LSGM solid electrolyte,respectively.The oxygen sensors with LSGMCo?x=0.9?,LSGCo?x=0.9?and LSGM dense diffusion barrier were prepared by the Pt sintered-paste method,respectively.The influences of temperature,oxygen content and L on sensing performance of oxygen sensors were investigated.The results showed that the limiting current oxygen sensors exhibited excellent limiting current plateaus in a wide range of oxygen content and temperature.The IL depended linearly on the oxygen contents,and logIL depended linearly on 1000/T.The IL decreased with increasing of L value.