Hydrothermal preparation of apatite-type phases La9.33Si6O26 and La9M1Si6O26.5 (M = Ca,Sr,Ba)

Apatite-type lanthanum silicates show a great potential to be used as an electrolyte for intermediate-to low-temperature (600-700 °c) solid oxide fuel cells (itsofc). however,so far these materials need to be prepared using a very high-temperature method,thus there is a growing interest to prepare apatites at lower temperatures. this paper reports the synthesis of undoped la9.33si6o26 and doped apatites (la9casi6o26,5,la9srsi6o26,5,and la9basi6o26,5) from raw materials la2o3,na2sio4,baco3,caco3,and srco3 using a hydrothermal method. the polycrystalline apatites were obtained as a white powder,after the basic solution of the reagent mixture was heated at 240 °c in an autoclave for 3 days. le bail refinement of the x-ray powder diffraction data showed that the compounds have a hexagonal cell (p 63/m space group). in this paper,the undoped la9.33si6o26 and la-doped apatite ionic conductivities are also presented. © 2012 published by lppm itb.