Low-temperature sintering of dense lanthanum silicate electrolytes with apatite-type structure using an organic precipitant synthesized nanopowder

Abstract

Highly sinterable La(10)Si(6)O(27) and La(10)Si(5.5)M(0.5)O(27) (M = Mg, and Al) nanopowders with apatite-type structure have been synthesized via a homogeneous precipitation method using diethylamine (DEA) as a precipitant. The synthetic approach using an organic precipitant with dispersant characteristics is advantageous in configuring weakly agglomerated nanopowders, leading to desirable sintering activity. X-ray diffraction powder patterns confirmed the single-phase crystalline lanthanum silicate of hexagonal apatite structure at 800 degrees C, which is a relatively lower calcination temperature compared to conventionally prepared samples. Transmission electron microscopy images revealed particles similar to 30 nm in size with a high degree of crystallinity. A dense grain morphology was recognized from the scanning electron microscopy images of the polished Surface of the pellets that were sintered at 1400 and 1500 degrees C for 10 h. This low-temperature sintering is significant because conventional powder processing requires a temperature above 1700 degrees C to obtain the same dense electrolyte. The doped-lanthanum silicate electrolyte prepared by the DEA process and sintered at 1500 degrees C for 10 h exhibited electrical conductivity comparable with samples prepared at Much higher sintering temperature (>1700 degrees C).