Preparation And Study Of Apatite-type Lanthanum Silicate Electrolytes

Solid oxide fuel cells (SOFCs) are devices that can convert chemical energy directly into electrical energy efficiently. Traditional high-tempreture fuel cells must be operated at more than 1000℃which results in some troubles and restricts the commercialization of SOFCs.The operation of SOFCs at intermediate tempreture becomes an inexorable trend. And this requires using a thin solid electrolyte film or a high oxide ionic conductivity at intermediate tempreture. Using apatite lanthanum silicate which has low activation energy and high oxide ionic conductivity at intermediate tempreture as electrolyte material for SOFCs may realize the further development of SOFCs.A thin film electrolyte can reduce its internal resistance and raise its conductivity for SOFCs. The apatite lanthanum silicate films (La10Si6027) studied in this paper are made by magnetron sputtering. The phase, surface morphology, thickness and conductivity of the film obtained by magnetron sputtering are mainly detected by XRD, SEM and so on. The parameters which affect formation of apatite phase by magnetron sputtering are:work pressure, substrate tempreture, annealing tempreture and annealing time. The experimental results indicate that the best parameters are:RF power:80w, work pressure:0.5Pa, substrate tempreture:room tempreture, annealing tempreture:1100℃, annealing time:6h. The phase of the obtained electrolyte film under this condition is La9.33Si6O26.The film is density and the thickness is 0.77p.m. The conductivity of the film at 800℃is 9.45×10-2S·cm-1 and activation energy is 0.98eV.Mg-doped apatite lanthanum silicate is one of those which have highest oxide ionic conduntivity.Because the powder obtained by sol-gel has high sintering activity which can make the apatite lanthanum silicate dense at lower tempreture, the apatite lanthanum silicate plates made by sol-gel are studied in this paper. The chemical formula of the electrolyte material of apatite lanthanum silicate made by sol-gel is La10Si5.8Mg0.2O26.8.The phase, morphology of the powder and density, morphology, conductivity of the sintered ceramic plates are seperately detected by XRD, SEM, TEM, vernier caliper, precision balance and so on. When the podwer (La10Si5.8Mg0.2026.8) was calcined at 900℃and then sintered at 1500℃, the sample shows the best results. The particles of obtained powder is about 100nm in size. The density of ceramic plate is 86.1%, the conductivity at 800℃is 1.09×10-2S·cm-1 and the activation energy is 0.62eV.