XPS surface analyses of LaPO4 ceramics prepared by precipitation with or without excess of PO43-

Lanthanum phosphate (LaPO4) powders were synthesized by precipitation with and without excess of phosphate and sintered at 1450 degreesC. Bulk and surfaces of different origin and treatments were investigated using powder x-ray diffraction, transmission electron microscopy and x-ray photoelectron spectroscopy. The XPS data are reported and interpreted in some detail, and they indicate that phosphate excesses do remain in surfaces and appear to be accompanied by sodium accumulated in the surface from an unknown source. It is likely that grain boundaries are similarly phosphate enriched and a generally higher electrical conductivity of phosphate-excess LaPO4 samples is discussed in view of this. Copyright (C) 2002 John Wiley Sons, Ltd.