A rare earth L-3-edge EXAFS and L-1-edge XANES study of Ce, Nd and Eu phosphate glasses and crystals in the composition range from metaphosphate to ultraphosphate

Rare earth (R) phosphate glasses, (R2O3)(x)(P2O5)(1-x), can be prepared with compositions in the range from ultra-phosphate,x = 0.17 (RP5O14), to metaphosphate, x = 0.25 (RP3O9), and it is important to know whether the R-O coordination changes significantly with composition. In rare earth phosphate crystals, the number of nearest neighbour oxygens changes from eight for ultraphosphate to six for metaphosphate. These R-O correlations are clearly distinguished in L-3-edge extended X-ray absorption spectroscopy (EXAFS) of NdP5O14 and EuP3O9 crystals. Samples of Ce (x = 0.197 and 0.235), Nd (x = 0.187) and Eu (x = 0.218) phosphate glasses all show the same EXAFS and L-1-edge X-ray absorption near edge structures (XANES) results. The results indicate an R-O coordination with six nearest neighbour oxygens, a similar level of static disorder to that in rare earth phosphate crystals and reduced centrosymmetry. There is no evidence for a change in R-O coordination with changing x. (C) 2001 Elsevier Science B.V. All rights reserved.