Amorphous oxide glass

Diffusion coefficients in amorphous solids such as oxide glasses and glasslike amorphous metals can be measured using any of the methods applicable to crystals. In this way it is possible to obtain the diffusion coefficients of, say, alkah and alkaline earth metals in silicate glasses or the diffusion of metal impurities in amorphous alloys. Unlike diffusion in crystals, diffusion coefficients in amorphous solids tend to alter over time, due to relaxation of the amorphous state at the temperature of the diffusion experiment. 

Voigt [1705] prepared transparent Ge02 glasses on hydrolysis of Ge(OEt)4 the temperature of glass formation is about l(XfC lower in comparison with that used in conventional methods. On crystallization of amorphous oxide prepared on hydrolysis of Ge(OPri)4, a mixture of two phases, crystoballite and a-quartz, is formed. On further thermal treatment, phase transition of crystoballite to a-quartz occurs, while grinding in air results in the transition to a rutile-type structure on treatment at temperatures higher than 1050°C all phases are tranferredto a-quartz [1766]. 

Amorphous materials have no long-range structural order, so there is no continuous lattice in which atoms can vibrate in concert in order for phonons to propagate. As a result, phonon mean free paths are restricted to distances corresponding to interatomic spacing, and the (effective) thermal conductivity of (oxide) glasses remains low and increases only with photon conduction (Figure 8.2). 

Some examples of sohd electrolytes are presented in Table 1. In the hmited scope of this article, only a few examples of some of the most important (i.e. for potential commercial apphcations) monovalent cation (Li+, Na+, and H+) and anion (oxide and fluoride) conductors will be discussed. Amorphous materials, glasses, and polymers are treated in Section 4. However, it should be noted that relatively good ionic conductors are known with many other monovalent ions including K+, Rb+, Cu+, T1+, and Ag+, divalent ions, for example, Pb +, Ca +, Ba +, Zn +, Sn + in jS -alumina, and even trivalent cations,and tetravalent cations. In Section 5, the application of some of these materials in electrochemical devices including batteries, sensors, smart windows and fuels cells are discussed. 

The arrangement of the atoms or ions in the material also needs to be considered. Crystalline ceramics have a very regular atomic arrangement whereas in noncrystalline or amorphous ceramics (e.g., oxide glasses) there is no long-range order, although locally we may identify similar polyhedra. Such materials often behave differently relative to their crystalline counterparts. Not only perfect lattices and ideal structures have to be considered but also the presence of structural defects that are unavoidable in all materials, even the amorphous ones. Examples of such defects include impurity atoms and dislocations. 

The situation is much more complicated in glasses with a complex network structure, for example, as in the oxide glasses, the simplest of which is amorphous SiO. There is much literature on the interpretation of these spectra (Simon (1960), Zarzycki and Naudin (1960), Su et al (1962) and others). Bell et al (1968) constructed three dimensional models of Si02, Ge02 and Bep2 glasses with typical atomic arrangements, then made plausible assumptions about the force constants, and calculated the frequency distributions of the vibrations. A similarity of observed infrared and Raman spectra with computed results was shown to exist. However, they did not calculate the optical and Raman matrix elements. 

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