EXAFS studies of rare-earth metaphosphate glasses

Abstract

An extended x-ray-absorption fine structure (EXAFS) study has been carried out on a range of rare-earth metaphosphate (Formula presented) glasses of growing interest in optical communications and laser technologies. Phosphate glasses modified using the rare-earth oxides (Formula presented)(Formula presented), (Formula presented)(Formula presented), (Formula presented)(Formula presented), (Formula presented)(Formula presented), (Formula presented)(Formula presented), and (Formula presented)(Formula presented), have been investigated using their respective rare-earth (Formula presented) absorption edges. The data provide information on the local environment of the rare-earth ion within the phosphate glass matrix constructed from linked P(Formula presented) tetrahedra. The rare-earth ions occupy sites with an average coordination number in the range, (Formula presented), the surrounding atoms being oxygen. The first shell interatomic distance over the range of rare-earth ions establishes the rare-earth contraction of ionic radii with increasing atomic number in a series of glasses. There is also evidence for a rare-earth-phosphorus correlation between 2.7 and 3.6 Å, and a further rare-earth-oxygen correlation at approximately 4 Å. The EXAFS spectrum shows no evidence for R-R correlations within the short-range order, a result especially pertinent to the optical and magnetic properties of the glasses. The fractal dimensionality 4(Formula presented)/B of these glasses, obtained from the elastic stiffnesses determined from ultrasonic wave velocities, ranges between 2.3 and 2.8, indicating that their connectivity tends towards having a three-dimensional character. © 1996 The American Physical Society.