A rare-earth K-edge EXAFS study of rare-earth phosphate glasses, (R2O3)(x)(P2O5)(1-x), x=0.187-0.239, R = La, Nd, Sm, Eu, Gd, Dy, Er

A rare-earth K-edge extended x-ray absorption fine structure (EXAFS) study of rare-earth phosphate glasses, (R2O3)(x)(P2O5)(1-x), x = 0.187-0.239, R = La, Nd, Sm, Eu, Gd, Dy, Er, is presented. The structures of these material s were investigated as a function of (a) rare-earth atomic number and (b) t emperature, and represent some of the first rare-earth K-edge EXAFS studies on a series of lanthanide-based materials. Results corroborate findings fr om complementary x-ray and neutron diffraction and magic-angle-spinning (NI AS) NMR experiments, and in addition, they provide a unique insight into th e nature of the static disorder of the R-O correlations and of the neighbou ring phosphate groups. The effects of multiple-scattering contributions are also discussed within this context. The variable temperature measurements illustrate the exceptionally high level of network rigidity present in thes e materials. The results are also compared to those obtained from an analog ous rare-earth L-III-edge EXAFS (5.483-8.358 keV) study. Results show that the use of the much higher energies of the rare-earth K-edge (38.925-57.486 keV) enable one to avoid the double-electron excitation problems that are associated with the rare-earth L-III-edge EXAFS in the dynamic range of int erest. EXAFS fitting and deconvolution simulations show that the large core hole lifetimes associated with the rare-earth K-edge do not significantly detract from the results. The deconvolution. studies also corroborate our f indings that the level of fitting to our data cannot realistically be expan ded beyond the first R-O shell. This limitation exists despite the exceptio nal counting statistics of the experiment and the highly uniform samples ma de possible by the ability to use much thicker samples at the higher energi es compared to those used for the (higher absorption) rare-earth L-III-edge EXAFS studies.