| Solid oxide fuel cell is a kind of high efficient, clean, convenient and practical energyconversion device. Solid electrolyte is the most important part of solid oxide fuel cells, and itsperformance determines directly the battery work temperature and performance. Apatite-typelanthanum silicate which shows high conductivity, low activation energy and high chemicalstability at low temperatures is concerned extensively as medium temperature SOFCelectrolyte material.Firstly, apatite-type lanthanum silicate electrolyte was prepared by solid state reaction.The samples crystal phase composition and surface morphology were characterized by meansof X-ray diffraction （XRD） and scanning electronic microscope （SEM）, respectively. Theresults proved the apatite samples were obtained as sintered at1500℃for30h. The sampledensities were determined through the Archimedes method, showing that density increasedwith the increase in sintering time. We investigated conductivity properties of the samples.The results showed that the relationship between conductivities and temperatures followedbasically Arrhenius equation. We found that the conductivities increased as the samplerelative densities increased. The maximum conductivity of1.1×10-2S cm-1was obtained forthe apatite sample sintered1500℃for30h when the raw materials molar ratio was1:1.1（La2O3-1.1SiO2）..Secondly, we studied the synthesis of La-substituted lanthanum silicate and theirconductive properties. La9.33（1-x）Ca9.33xSi6O26and La9.33（1-x）Mg9.33xSi6O26（x=0,0.1,0.2,0.3,0.4） were prepared at1440℃with solid state reaction. XRD proved the apatite samples wereobtained. We investigated further conductivity properties of the samples. The results showedthat the relationship between conductivities and temperatures basically followed Arrheniusequation, Compared with pure apatite lanthanum silicate, the substitution of Mgã€Ca inLa-location reduced the sintering temperature and sintering time of samples. Theconductivities of La-substituted apatite are mainly influenced by four factors:（1） thenumber of cation-vacancy;（2） the ionic radius of substituting elements;（3） the substitutingamount of elements;（4） the sample density. The conductivities of the samplesLa9.33（1-x）Ca9.33xSi6O26（x=0.1） reach the maximum value of1.88×10-2S cm-1.Thirdly, we studied the synthesis of Si-substituted lanthanum silicate and theirconductive properties. La9.33Si6（1-x）Ga12xO26+δand La9.33Si6（1-x）Ge6xO26（x=0,0.1,0.2,0.3,0.4） were prepared at1440℃with solid state reaction. XRD proved the apatite samples wereobtained. We investigated further conductivity properties of the samples. The results showedthat the relationship between conductivities and temperatures basically followed Arrheniusequation, Compared with pure apatite lanthanum silicate, the substitution of Gaã€Ge inSi-location reduced the sintering temperature and sintering time of samples. Theconductivities of Si-substituted apatite are mainly influenced by four factors:（1） the numberof cation-vacancy;（2） the ionic radius of substituting elements;（3） the substituting amount ofelements;（4） the ionic charge number of substituting elements;（5） the sample density. |
