Because the structure of a glass represents that of the solid “frozen‐in” at the glass transition, it is also important to investigate the marked temperature‐induced structural changes that take place in melts at higher temperatures. In this regard, two cases should be distinguished depending on the differences between the experimental timescale of the method and the rate of structural change of the melt. If the former is very short with respect to the latter, then the result will be a snapshot of a solid‐like structure; if it is long, the result will represent a time‐averaged structure that brings little information on the individual features that are averaged (see Section 4).
Table 1 Summary of techniques used to determine various features of glass structure.
| Technique | Energy (eV) | Frequency (Hz) | Wavelength (nm) | Process | Information obtained |
|---|---|---|---|---|---|
| X‐ray diffraction | 0.1–100 keV | 3 × 1016–3 × 1019 | 0.01–10 nm | Scattering/diffraction from electrons | ~0–15 Å, quantitative bond lengths and angles over short‐ and intermediate‐range length scales |
| Neutron diffraction | 0.1–500 meV | 0.04–120 THz | 0.04–3 nm | Scattering/diffraction from neutrons | ~0–15 Å, quantitative bond lengths and angles over short‐ and intermediate‐range length scales, dynamics |
| EXAFS | 0.1–100 keV | 3 × 1016–3 × 1019 | 0.01–10 nm | Atom‐specific absorption of X‐rays, multiple scattering | ~5–6 Å, quantitative atom‐specific bond lengths and coordination |
| XANES | 0.1–100 keV | 3 × 1016–3 × 1019 | 0.01–10 nm | Atom‐specific electronic transitions to unoccupied orbitals, multiple scattering | ~1–3 Å, qualitative coordination, oxidation state, electronic structure |
| XRS | Usually <10 keV | 2.4 × 1013–3.4 × 1017 | ~1–1000 nm | Energy loss of inelastically scattered X‐ray photons | In‐situ high‐pressure energy loss spectra of low z elements (equivalent to XANES), short‐range structure, electronic structure |
| XPS | ~0.1–1400 eV | 2.4 × 1013–3.4 × 1017 | ~1–3000 nm | Energy of ejected core and valence electrons | Oxygen speciation (BO, NBO, free oxygen) |
| EELS/ELNES | 10 meV–10 keV | 7.2 × 1011–2.9 × 1017 | ~1–1000 nm | Energy loss of transmitted electrons through the sample | Same as XANES |
| IR | 886 meV–3eV | 430 × 1012–300 × 109 | 1 mm–2500 nm | Molecular vibrations | Vibrational states, quantification of CO2/H2O in glasses, coordination states, short‐ and intermediate‐range structure |
| Raman | 1.2–120 meV | 3 × 1011–1.5 × 1014 | 0.5 mm–1000 nm | Molecular vibrations, inelastic photon interactions | Vibrational states, Q species, ring statistics, short‐ and intermediate‐range structure |
| Brillouin | 1.2 × 10−3–7.4 × 10−4 eV | 107–1.8 × 1011 | 100–1000 nm | Inelastic photon–phonon interactions | Elastic and acoustic properties |
| UV/Vis | 1.7–124 eV | 30 × 1019–790 × 1012 | 10–700 nm | Valence electron transitions | Oxidation and coordination states of transition metals |
| NMR | 12.4 peV–1.24 meV | 3 × 103–300 × 109 | ~1 km–1 mm | Nuclear spin interactions | Short‐ and intermediate‐range structure, bond angles, coordination states, Q species, dynamics |
| Mössbauer | 100 keV | >1019 | <0.1 nm | Nuclear transitions | Oxidation state and coordination of Mössbauer active nuclei: typical Fe, Sn in glasses |
In order to select the most suitable technique for probing the glass of interest, one has to determine what aspect of the structure is to be probed (bulk or atom specific), and what is the length scale to be probed (short‐range, intermediate‐range, or extended‐range)? In many instances more than one technique will need to be employed. I will briefly discuss a number of common and not so common techniques for deriving structural information on glasses. Whereas space constraints limit the detail that can be provided, I will provide a general overview of what aspect of the structure is probed and what information can be determined from each method. The reader should refer to any of a number of detailed reviews of the specific techniques currently available (e.g. [1, 2]).
Acronyms
3Qtriple quantumAFMatomic force microscopyAWAXSanomalous wide angle X‐ray scatteringBEbinding energyBObridging oxygenCNcoordination numberDAXSdiffraction anomalous X‐ray scatteringEELSelectron energy‐loss spectroscopyELNESenergy loss near‐edge spectroscopyeVelectron voltEXAFSextended X‐ray absorption fine structureFIDfree induction decayFSDPfirst sharp diffraction peakFT‐IRFourier transform infraredFWHMfull width at half maximumHRTEMhigh‐resolution transmission electron microscopyIRinfraredIROintermediate‐range