Defect formation, glasses

Gamma-irradiation has been used to investigate effects on chemical durability of waste glasses (Lutze 1988) and to assess the effect on corrosion and defect formation in waste ceramics (Vlasov et al. 1987 Kulikov et al. 2001). Irradiation with Y-rays does not produce atomic displacements, but rather causes excitations and point defects and leads to formation of ion radicals. Therefore, this method may serve as a simulation for p-Y-radiation of FPs in the waste forms. 

It follows from the fit presented in Fig. 46 that Eb energies for all porous glass samples are about the same value of 33 kJ mol-1. However, for sample B the value of Eh is about 10% less than those for samples A and C. This fact can most likely be explained by the additional chemical treatment of sample B with KOH, which removes the silica gel from the inner surfaces of the pore networks. It is reasonable to assume that the defects generally form at the water interfaces, and only then penetrate into the water layer. Thus, it seems that the KOH treatment decreases the interaction between the water and inner pore surfaces and, consequently, decreases the defect formation energy Eb. 

Hydrogen can be forced at high pressure into the structure of silica-germania glasses. It has been proposed that the photosensitivity of these materials is related to the formation of Si-OH, so that in defect-free glasses the photoactivity depends on the presence of hydrogen. The H NMR characteristics of the different hydrogen centres... 

Hosono, H., Mizuguchi, M., Kawazoe, H., and Ogawa, T., Effects of fluorine dimer excimer laser radiation on the optical transmission and defect formation of various types of synthetic SiOj glasses, Appl. Phys. Lett. 74, 2755 (1999). 

Kajihara, K., Hirano, M., Skuja, L., and Hosono, H., Co y-ray-induced intrinsic defect processes in fluorine-doped synthetic SiOj glasses of different fluorine concentrations. Mater. Sci. Eng. B 161, 96 (2009). Kajihara, K., Ikuta, Y., Hirano, M., and Hosono, H., Power dependence of defect formation in SiOj glass by Fj laser irradiation, Appl. Phys. Lett. 81, 3164 (2002). 

Glass devitrification Formation of crystals (seeds) in a glass melt, usually occurring when the melt is too cold. These crystals can appear as defects in glass fibers. 

Kokura, K., Tomozawa, M. and MacCrone, R.K. (1989) Defect formation in SiOz glass during fracture. J. Noncryst. Solids, ill 269-276. 

Defects in glass can result in new resonance frequencies or absorption bands, which facilitate two-photon absorption. Defects resulting in absorption bands in the VIS or UV spectrum are called colour centres. Such colour centres can also be generated by exposing glasses to X-ray or electron radiation, which results in the formation of a bonded electron-hole-couple (exciton) (e - -h+). The generation of various colour centres in fused silica is described in the literature [138]. 

Apart from these, there are volume defects that cannot conveniently be described in any other terms. The most important of these consist of regions of an impurity phase—precipitates—in the matrix of a material (Fig. 3.39). Precipitates form in a variety of circumstances. Phases that are stable at high temperatures may not be stable at low temperatures, and decreasing the temperature slowly will frequently lead to the formation of precipitates of a new crystal structure within the matrix of the old. Glasses, for example, are inherently unstable, and a glass may slowly recrystallize. In this case precipitates of crystalline material will appear in the noncrystalline matrix. 

Non-lattice sites may play an important role in the incorporation of large foreign ions in crystal structures during coprecipitation Pingitore (Chapter 27) discusses the importance of these sites in the formation of coprecipitates of calcium carbonate containing Srz+ or Ba. White and Yee (Chapter 28) discuss the diffusion of alkali ions into defect structures in the surfaces of glasses and crystalline feldspars. 

Bogomolova, L. D., Stefanovsky, S. V., Teplyakov, Y. G. Dmitriev, S. A. 1997. Formation of paramagnetic defects in oxide glasses during the bompardment of their surface with charged particles. Materials Research Society Symposium Proceedings, 465, 657-664. 

The ionization of focal volume, or formation of plasma, is expected to alter the usual photochemical material modihcation pathway, as has been recently demonstrated in photopolymerization of SU-8 resist by femtosecond pulses [57]. In addition, nanometric-sized plasma regions created by the ionization, e.g., at defect sites, have spatio-temporal dynamics of their own. Recently, a model of nanosheet formation from plasma nanospheres in glass has been proposed [60]. Similar conditions are expected in polymers as well. Let us discuss here held enhancement by a metalhc nanoparticle (similar arguments are also valid for surfaces containing nanometric features). 

---