An extended x-ray absorption fine structure study of rare-earth phosphate glasses near the metaphosphate composition

A variable-temperature (79, 145, and 293 K) extended x-ray absorption fine structure study, using rare-earth L-III absorption edges, is reported for phosphate glasses doped with rare-earth elements (R, where R = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Er) with compositions close to metaphosphate, R(PO3)(3). The results yield nearest-neighbor R-O distances that demonstrate the lanthanide contraction in a glassy matrix and an R-O coordination intermediate between 6 and 7 for ran-earth ions with smaller atomic number (Z) and 6 for rare-earth ions with larger Z, Thermal parameters show no significant changes in R-O distances or coordination numbers between 293 and 79 K. There is evidence of an R-P correlation between 3.3 and 3.6 Angstrom and the beginning of a second R-O correlation at approximately 4 Angstrom. No R-R correlations up to a distance of approximately 4 ii were observed.