Vacancy complexes

BerG83 Berces, G., Kovacs, I. Vacancies and vacancy complexes in binary alloys. Phil. Mag. A. 48 (1983) 838-901. 

Note that we can use the same statistical mechanical approach to calculate SchottslQi" pairs, Frenkel pairs, divancies (which are associated vacancies), impurity-vacancy complexes, and line dislocation-point defect complexes. 

Evidence emerges from both the microcatalytic and spectroscopic studies for enhanced dissociative interaction of N,0 with preoxidised RhO,/CeO, materials exposed to helium-flush or vacuum-outgassing at T > 573 K. This is consistent with generation of reduced active-sites, such as electron-vacancy complexes, by such treatments. 

A number of the well-known y-induced centers in n-type Si are also neutralized by atomic hydrogen (Pearton, 1982). The A-center (oxygen-vacancy complex, Ec-0.18eV and divacancy level (Ec-0.23eV) are passivated, while the E-center (phosphorus-vacancy complex, Ec -0.44 eV) is thermally removed at relatively low temperatures and its susceptibility to hydrogenation could not be determined. Point defects... 

Intrinsic Crystal Self-Diffusion. A simple example of intrinsic self-diffusion in an ionic material is pure stoichiometric KC1, illustrated in Fig. 8.11a. As in many alkali halides, the predominant point defects are cation and anion vacancy complexes (Schottky defects), and therefore self-diffusion takes place by a vacancy mechanism. For stoichiometric KC1, the anion and cation vacancies are created in equal numbers because of the electroneutrality condition. These vacancies can be created... 

Electron paramagnetic resonance measurements only identify vacancies or vacancy complexes in Si irradiated by electrons. The absence of Si self-interstitials has been ascribed to rapid athermal migration even at 2 K (13). 

The presence of a shallow acceptor level in GaN has been attributed to C substituting on an N site by Fischer et al [7], In luminescence experiments on GaN from high temperature vapour phase epitaxy in a C-rich environment donor-acceptor and conduction-band-to-acceptor transitions have been distinguished in temperature dependent experiments. From the separation of both contributions an optical binding energy of 230 meV close to the value of effective mass type acceptors was obtained. Hole concentrations up to 3 x 1017 cm 3 were achieved by C doping with CCU by Abernathy et al [10], In addition Ogino and Aoki [17] proposed that the frequently observed yellow luminescence band around 550 nm should be related to a deep level of a C-Ga vacancy complex. The identification of this band, however, is still very controversial. 

It is useful to point out the similarity between the YL in GaN and the so-called self-activated (SA) luminescence in II-VI compounds. Metal vacancies and their complexes with donor impurities are well known in II-VI compounds (e.g. ZnS, ZnSe). The metal vacancy complexes (the so-called SA centres) exhibit features which are strikingly similar to the YL recombination between a shallow donor-like state and a deep acceptor state, and a broad luminescence band of Gaussian shape [22,23]. 

FIGURE 3 Formation energy as a function of Fermi level for Mg, nitrogen vacancies, interstitial H and hydrogen-vacancy complexes in GaN [1,14],... 

On defective surfaces, for example after Ar bombardment, surface states appear in the band gap region [203]. They were assigned to Ti -O-vacancy complexes [202]. Various reconstructions have been observed on vacuum annealed surfaces (2 x 2) [204], ( /5 x /5)R26.6° [205-208], c(2 x 2)[209]. They were assigned to an ordering of oxygen vacancies, the latter reconstruction being possibly due to Ca segregation on the surface. Simula-... 

One of the most important practical applications of lithium compounds is as fast ion conductors with potential electronic applications such as solid electrolytes for lithium batteries. Li20 is a fast ion conductor in which the Li ions occupy a simple cubic sublattice with the antifluorite structure. Both MAS and static Li NMR spectra of Li20 have been reported, the former recorded as a function of temperature up to 1000 K (Xie et al. 1995). The effect of introducing vacancies on the Li sites by doping with LiF has been studied by high-temperature static Li NMR, which reveals the interaction of the Li defects > 600 K and the appearance of 2 distinct quadrupolar interactions at about 900 K. Measurements of the relative intensities of the satellite peaks as a function of temperature have provided evidence of thermal dissociation of an impurity-vacancy complex (Xie et al. 1995). 

In spite of its rigid structure in solution and the trans disposition of the hydride and the coordination vacancy, complex 1 reacts with terminal alkynes to afford alkenyl derivatives, as a result of the addition of the Ru-H bond to the carbon-carbon triple bond of the alkynes [9]. In all cases, the alkenyl ligands have an -stereochemistry and lie in the apex of a square pyramid similar to that of 1. This property along with the presence of the chloride ligand allows the entry to C[, C2, C4, and SH fragments into the coordination sphere of the ruthenium. 

The ESR spectrum of Mn in sodium azide [28] shows a remarkable similarity to that of Mn in sodium chloride. In both cases the divalent manganese ion is located substitutionally at a monovalent sodium ion site, and the extra positive charge is compensated by a cation vacancy. The same mobility and coagulation effects are seen for both materials, and multiple sets of Mn —cation vacancy complexes are also observed. Vacancy hopping, which produces lifetime broadening of the resonance lines, is observed in NaNa (as well as in potassium and rubidium azides). As mentioned earlier. Miller and King [13] used the ESR spectrum of Mn " to observe the phase transition at 19°C. 

Comparison of both x, and S curves, confirms that stage 1 effectively corresponds to an SRO process assisted by excess vacancies, because in all cases it goes to completion just as the vacancy supersaturation vanishes. Moreover, both curves exhibit symmetrical kinetic paths. It is then inferred, necessarily, that during stage 2 the ordering process must be completed, assisted by equilibrium vacancies and by vacancy complexes which were not yet eliminated during stage 1. 

Nagai et al. have reported results from the study of Fe-0.3 wt% Cu, Fe-0.15 wt% Cu and Fe-0.05 wt% Cu alloys irradiated at 8.3 x 10 n/cm E > 1 MeV at -300 °C (the irradiation time was 144 hours) - see Fig. 9.31. As a result of CDB and positron hfetime measurements on irradiated and annealed samples, the authors reported the formation of microvoids (-10 vacancies), dislocation loops and Cu-mono-vacancy complexes. They considered that the micro-voids were decorated with Cu in all the alloys studied, and that in all cases the micro-voids were almost completely coated with Cu. After electron irradiation, ° vacancy clusters and single vacancies surrounded by Cu (v-Cu , where n > 6) were observed in electron-irradiated Fe-Cu, vacancy clusters were observed in Fe-Ni and Fe-P, but no vacancy clustering in Fe-C, Fe-Si or Fe-Mn was observed. 

Tateyama Y, Ohno T. Stability and clusterization of hydrogen-vacancy complexes in Fe An ab initio study. Phys. Rev. B 2003 67 174105. 

K20sBr6-K2SnCl6 ( Cl produced by (n,y) reaction) (Muller et al. 1986). In the latter case, the production of transient ligand vacancy complexes and their final fates resulting in mixed hexachlorobromometallate species are shown in the following scheme. 

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