| The acceptor-doped Ce O2 is an oxygen ion conductor with excellent performances,and has great application potential in the fields of oxygen sensors and solid oxide fuel cells(SOFC)and so on.It is of important practical significance to improve the stability of acceptor-doped Ce O2 at low oxygen partial pressure and oxygen ion conductivity at low temperature.It is an effective way to improve the electrical properties of acceptor-doped Ce O2 through controlling the microstructure of Ce O2-based materials and improving the preparation process,or adding a second phase to the doped Ce O2.Al2O3 is a common high-temperature ceramic sintering aid and grain refiner,which can increase the density and reduce the sintering temperature of Ce O2-based materials.Al2O3 can also suppress the electron conduction by means of"electron trapping"mechanism at the doped Ce O2 grain boundary.In recent years,some studies also show that the Ce O2/Al2O3 heterogeneous phase interface can help to increase the grain boundary conductivity of the sample.First,the Ce0.85Y0.15O1.925(YDC)ceramic with the average grain size of 70nm?1.26?m is prepared in 900?1500°C.The changes of grain,grain boundary and total conductivity of YDC samples were studied with the increase of grain size.The results of XRD and SEM show that all samples have a single YDC cubic phase and dense structure.At some test temperatures,the analysis of YDC electrical performance shows that the grain conductivity of YDC first decreases and then increases as the grain size of the sample decreases from 1260 nm to 70 nm.The grain boundary conductivity of YDC improves greatly when the grain size reduces to the range of nanometer size.But the total electrical property of nanometer-sized sample increases invisibly.The total conductivity is 0.015 S/cm at 650°C.At the same measure temperature,the total conductivity of YDC sintered at 1400°C for 3 h is the highest,being 0.019 S/cm.Then,the co-precipitation method was used to synthesize Ce0.85Y0.15O1.925(YDC)powders and composite powders of samples were prepared by Al2O3 sol.Ce0.85Y0.15O1.925-xmol%Al2O3(x=0,5,10,20,30)were sintered at 1300°C for 10 h.The effects of different addition amounts of Al2O3 on the electrical properties and micro-morphology of YDC were analyzed and studied by XRD,SEM,TEM and AC impedance.The XRD and SEM characterization results show that YDC-x%Al2O3only has two phases of Al2O3 and YDC.The average grain size of the sample is 330nm to 510 nm.The relative density of the sample increases first and then decreases with increasing of the addition amount of Al2O3.When the addition amount of Al2O3is 10%,the relative density reaches the maximum value of 95%.The relative density of all samples is higher than 91%.The AC impedance test results of YDC-x%Al2O3show that the effect of Al2O3 to the grain conductivity of YDC-Al2O3 composites is non-significant.In the test temperature range of 300°C?600°C,with the increasing of Al2O3 amount from 0 to 20%,the grain boundary and total conductivity of the sample decrease.When the content of Al2O3 increases from 20%to 30%,the conductivity shows an upward trend.In YDC-Al2O3,the grain boundary conductivity has a greater effect on the total conductivity.YDC-Al2O3 composite ceramics were sintered at 1300°C with a heating rate of50°C/min by spark plasma sintering(SPS)method.The results of XRD and SEM show the presence of YDC cubic phase in the multi-phase ceramics with different Al2O3 contents.When 5%Al2O3 is added to YDC,a second phase of Ce Al O3 is formed in the matrix.With the increase of Al2O3 amount,the average grain size of the sample decreases from 1.7?m to 0.34?m.At a certain test temperature,the AC impedance results show that,with the increase of Al2O3 amount,the grain conductivity of the samples increases to different degrees.The grain boundary and total conductivity first decrease and then increase. |
PDF Full Text Request