Sintering kinetics and oxide ion conduction in Sr-doped apatite-type lanthanum silicates, La9Sr1Si6O26.5

These last past years, a major interest has been devoted to decrease the working temperature of solid oxide fuel cells (SOFCs) down to about 700 degrees C. Apatite materials (La10-xSrxSi6O27-x/2) are attractive candidates for solid electrolytes, with a high ionic conductivity at these intermediate temperatures. An apatite powder (x = 1) with a 0.75 mu m mean particle size, produced by solid state reaction, was tape cast to obtain green sheets with a thickness of about 260 mu m. On one hand, the densification mechanism of the apatite ceramic during the intermediate solid state sintering has been approached. It appeared from the kinetical tests performed under isothermal conditions between 1250 and 1550 degrees C, that densification could be controlled by the diffusion at grain boundaries of the rare-earth element, La, with an activation energy of 470 kJ/mol. On the other hand, conductivity measurements were performed on apatite samples sintered at 1400 and 1500 degrees C. The ionic conductivity was mainly sensitive to the presence of secondary phases at 1400 degrees C. The ionic conductivity of the apatite sintered at 1500 degrees C (mean grain size = 3.9 mu m) is equal to 1.2 x 10(-2) S/cm at 700 degrees C. (C) 2009 Elsevier B.V. All rights reserved.