Glasses comparison with crystals

A similar analysis of a melt-crystallized poly(ethylene terephthalate), PET, of the typical molecular mass of a polyester showed a surprising reversing melting peak, as seen in Fig. 3.92. On comparison with an amorphous PET, one finds that the reversing peak depends on crystallization history, as is shown in Fig. 4.136. The change of the glass transition with crystallization is typical for polymers. It shows a... 

The sol-gel process to prepare SIO2 glass fibers and T102 films has been reviewed. It has been known that the hydrolysis conditions such as molar ratio of water to alkoxide and reaction temperature are critical to the desired forms of the gel product (fiber, film or bulk). Some properties of the resultant products have been examined. Especially, Ti02 films have been attempted to use as a photoanode for decomposition of water, and their photoelectrochemical properties are described in comparison with the results previously obtained for single crystal and polycrystalline TiC>2, and are discussed in terms of the microstructure of the film. 

Mossbauer Effect in Similar Glasses and Crystals. Expression of the Mg-Fe content of tektites in terms of enstatite-ferrosilite percentages suggests a comparison with silicate minerals which contain Fe and... 

In addition, the glass matrix has an essential merit in comparison with the solvent which crystallizes at low temperature. For example, Smith et al. irradiated several olefins at 77° K and examined their ESR spectra, and they found that the electrons were trapped in the frozen state of glass but never in the crystalline state (9). This is also the case with 3-methylpentane (70), and other compounds such as alcohols and ethers. This fact may imply that the radiation-formed ionic intermediates are much more stable in the glass matrix than in the crystalline matrix, though the reason has not yet been confirmed. 

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]. 

Crystal field spectral measurements of transition metal ions doped in a variety of silicate glass compositions (e.g., Fox et al., 1982 Nelson et al., 1983 Nelson and White, 1986 Calas and Petiau, 1983 Keppler, 1992) have produced estimates of the crystal field splitting and stabilization energy parameters for several of the transition metal ions, examples of which are summarized in table 8.1. Comparisons with CFSE data for each transition metal ion in octahedral sites in periclase, MgO (divalent cations) and corundum, A1203 (trivalent cations) and hydrated complexes show that CFSE differences between crystal and glass (e.g., basaltic melt) structures,... 

Cp is estimated on the basis of 7.6 cal mol by comparison with the liquid phases of LiF, BeF2 snd Li BeF. A glass transition is assumed at 400 K and below this temperature Cp is obtained from that of the crystal. The entropy is calculated in a manner analogous to that used for Note that the resulting value of S"(900) differs by only 0.08 cal mol from... 

A glass transition was assumed at 1000 K. The heat capacity below 1000 K was obtained from the heat capacity of the crystal. Above 100 K the heat capacity was assumed constant and estimated as 38.0 cal K mol by comparison with those for MgClgCO. KCl(t) and KgSO (t). S°(t, 298.15 K) is calculated in a manner analogous to that used for the enthalpy of formation. 

Aside from these approaches, empirical relations have been proposed to relate the second- and third-order nonlinear susceptibilities to their linear analogs. Among them are Miller s rule [209] for the second-order nonlinear susceptibility of ionic crystals as well as the expressions of Wang [210] and of Boling, Glass, and Owyoung [211] for the third-order nonlinear susceptibility in the low-frequency limit. The latter have been shown, by comparison with experiment, to possess their own range of validity. 

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