Deposition Of Thin Electrolyte Film Of Apatite-type Lanthanum Silicate For SOFCs Operated At Low And Intermediate Temperature By Magnetron Sputtering

Solid oxide fuel cells (SOFCs) is a kind of solid chemical electricity device which can directly convert the energy in the fuel and oxidant into electricity effectively and environment friendly. At present, the trend of SOFCs development is to reduce the operating temperature to low and intermediate ranges. Its operating temperature can be reduce by the ways as follows: (1) using the electrolyte film; (2) useing the electrolyte with high conductivity at medium-low temperature. Apatite-type lanthanum silicate is attractive for applicantion as a medium-low temperature solid oxide fuel cells electrolyte owing to its advantages of high conductivity at medium-low temperature and chemical stability. Solid state reaction is a common method for the preparation of Apatite-type lanthanum silicate, but the sintering temperature is high and apatite-type lanthanum silicate is non densification. Applying Magnetron sputtering to produce apatite-type lanthanum silicate electrolyte membrane is expected to solve the dense problem that it is difficult to prepare apatite-type lanthanum silicate under the low temperature. Meanwhile, the film of electrolyte can decrease the resistance of SOFCs and further reduce the operating temperature of SOFCs.Apatite-type lanthanum silicate target was prepared by solid state reaction. By using of precision scales and vernier caliper, the weight and size of targets were measured. According to formula, the density of target can be determined. XRD, SEM and other testing methods were used to characterize the phase composition and surface morphology of the target. The results show that sintering at 1560℃, the density of the target is 73.9% and the main target is La9.33Si6O265; sintering at 1620℃, the density of target is 83.5%, the target for the main phase is La9.33Si6026.Thin electrolyte film of apatite-type lanthanum silicate was synthesis by magnetron sputtering. Firstly, in the experiment of preparation the electrolyte film, it was a serious shortage of La content by using only single-apatite-type lanthanum silicate targets. The reasons were the insufficient La content of the target and the low sputtering yield of La. Therefore, we used the apatite-type lanthanum silicate La target and the sputtering target of apatite-type lanthanum silicate electrolyte film. Apatite-type lanthanum silicate target and La target were made by RF sputtering and DC sputtering respectively. The electrolyte film composition, surface morphology, film thickness were characterized by EPMA, SEM, step device testing methods. Our optimal experimental parameters are:RF power 100W, DC power 11W, work pressure 0.8Pa, bias-45V. The optimal contents of electrolyte membrane are La 70.060wt%, Si 7.530wt%, Mg 0.063wt%, O 22.349wt%, molar ratio of La and Si 10:5.32. Electrolyte film is continuous and dense. Electrolyte film thickness is between 3μm and4μm, and the deposition rate is between 400nm/h and 500 nm/h.Magnetron sputtering of the electrolyte membrane was subject to annealing for apatite phase. The phase of electrolyte film was characterized by XRD. After annealing at 1100℃for 5h, the main phase of electrolyte films is apatite (La9.33Si6O26) phase. In addition, all of the electrolyte films after annealing contain La2Si2O7 phase and La2SiO5 phase.