The authors review the development of extended x-ray absorption fine structure (EXAFS) within the last decade. Advances in experimental techniques have been largely stimulated by the availability of synchrotron radiation. The theory of EXAFS has also matured to the point where quantitative comparison with experiments can be made. The authors review in some detail the analysis of EXAFS data, starting from the treatment of raw data to the extraction of distances and amplitude information, and they also discuss selected examples of applications of EXAFS chosen to illustrate both the strength and limitations of EXAFS as a structural tool.

Extended x-ray absorption fine structure—its strengths and limitations as a structural tool

Recent developments of phosphate glasses for a variety of technological applications, from rare-earth ion hosts for solid state lasers to low temperature sealing glasses, have led to renewed interest in understanding the structures of these unusual materials. In this review, spectroscopic and diffraction studies of simple phosphate glasses, including v-P2O5 and binary phosphate compositions, are described. Special attention is given to the structures of anhydrous ultraphosphate glasses, which have received close attention from the glass community only in the past six years.

Review: the structure of simple phosphate glasses

Raman spectroscopy studies of alkali and alkaline earth silicate glasses and melts are reviewed, and the major Raman bands observed are summarized. To realize the full potential of Raman spectroscopy will require a detailed understanding of their vibrational properties in relation to structure. A number of vibrational calculations have been carried out to address this problem. These are briefly summarized, and some limitations of the method are noted. Systematic variations in bulk properties are examined for viscosity and the immiscibility behavior.

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Structural studies of silicate glasses and melts—applications and limitations of Raman spectroscopy

Diffusion constants are typically considered to be independent of particle size with the benefit of nanosizing materials arising solely from shortened transport paths. We show that for materials with one-dimensional atomic migration channels, the diffusion constant depends on particle size with diffusion in bulk being much slower than in nanoparticles. This model accounts for conflicting data on LiFePO4, an important material for rechargeable lithium batteries, specifically explaining why it functions exclusively on the nanoscale.

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Particle size dependence of the ionic diffusivity.

The infrared reflectance spectra of lithium borate glasses (0–73 mol% Li 2 O) have been measured over a broad and continuous spectral range (30–4000 cm −1 ) in an attempt to study systematically their structure. The reflectance data have been analyzed by Kramers-Kronig inversion to obtain the optical and dielectric properties of the materials. The study of the deconvoluted mid-infrared spectra has revealed a glass network built up of various boron-oxygen groups, with structure and concentration strongly dependent on the Li 2 O content. Of particular interest was the far-infrared asymmetric absorption profile, which could be well simulated by two broad bands attributed to vibrations of lithium cations in two distinct network environments. The presence of these two Li + -host site distributions was found to be independent of the details of the borate network structure and has been taken to imply a more general characteristics of ionic conducting oxide glasses.

Infrared reflectance spectra of lithium borate glasses

We report the polarized Raman spectra, the infrared reflectivity, and the infrared dielectric constant of vitreous ${\mathrm{B}}_{2}$${\mathrm{O}}_{3}$, for vibrational frequencies up to 1800 ${\mathrm{cm}}^{\ensuremath{-}1}$. Longitudinal- and transverse-mode frequencies are identified. The dominant Raman line, at 808 ${\mathrm{cm}}^{\ensuremath{-}1}$, is extremely narrow (\ensuremath{\sim}15 ${\mathrm{cm}}^{\ensuremath{-}1}$) and is highly polarized, with peak intensities in the ratio HH/HV \ensuremath{\sim}28. (Here HH means that the incident and scattered electric vectors are parallel, while HV indicates that they are perpendicular.) The spectra are analyzed using a nearest-neighbor central-force network-dynamics model, and by comparison with data obtained from selected molecular species. The results favor a structural model containing a large fraction of boroxyl rings.

Vibrational spectra and the structure of pure vitreous B 2 O 3

Extended-x-ray-absorption-fine-structure investigation of mobile-ion density in superionic AgI, CuI, CuBr, and CuCl

Optical properties and electronic structure of crossroads material MnTe

The Raman spectra and structure of pure vitreous P2O5

We have used Raman spectroscopy to characterize the thermal treatment of several types of vitreous silica samples by monitoring the intensity of a strongly polarized mode at 606 cm−1. Room-temperature measurements were made on quenched samples as they were progressively equilibrated at the desired fictive temperatures. As the annealing temperature or network terminator concentration increased, the times required for equilibration decreased. The equilibrium intensity of the 606 cm−1 Raman line is exponentially dependent on the inverse fictive temperature, but independent of the impurity (such as OH) concentration. We reconcile this latter disagreement with other published results.

J.C. Mikkelsen

Papers

Vibrational spectra and the structure of pure vitreous B 2 O 3

Extended-x-ray-absorption-fine-structure investigation of mobile-ion density in superionic AgI, CuI, CuBr, and CuCl

Optical properties and electronic structure of crossroads material MnTe

The Raman spectra and structure of pure vitreous P2O5

Thermal equilibration of raman active defects in vitreous silica