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

摘要

A variable-temperature (79, 145, and 293 K)extended x-ray absorption fine structure study, using rare-earthL_III absorption edges, is reported for phosphate glasses dopedwith rare-earth elements (R, where R = La, Ce, Pr, Nd, Sm, Eu, Gd,Tb, Dy, Ho, and Er) with compositions close to metaphosphate,R(PO_3)_3. The results yield nearest-neighbor R-O distances thatdemonstrate the lanthanide contraction in a glassy matrix and an R-O coordination intermediate between 6 and 7 for rare-earth ionswith smaller atomic number (Z) and 6 for rare-earth ions withlarger Z. Thermal parameters show no significant changes in R-Odistances or coordination numbers between 293 and 79 K. There isevidence of an R-P correlation between 3.3 and 3.6A and thebeginning of a second R-O correlation at approximately 4 A. NoR-R correlations up to a distance of approximately 4A were observed.