Vacancies metals, small deviations from

Small deviation from stoichiometry. I. Metal vacancies... 

Let us consider the compounds which show a small deviation from the stoichiometric composition and whose non-stoichiometry is derived from metal vacancies. The free energy of these compounds, which take the composition MX in the ideal or non-defect state, can be calculated by the method proposed by Libowitz. To readers who are well acquainted with the Fowler-Guggenheim style of statistical thermodynamics, the method here adopted may not be quite satisfactory however, the Libowitz method is understandable even to beginners who know only elementary thermodynamics and statistical mechanics. It goes without saying that the result calculated by the Libowitz method is essentially coincident with that calculated by the Fowler-Guggenheim method. 

The glass s >strate is covered by a metallic film (Ag) which serves as a back contact. The heterojunction system is based on a CdS film (between lO and 30 ym thickness) which due to sulfur vacancies is n-type. On the top of the CdS film a Cu S film (x 2) is prepared which due to small deviations from stoichiometry is p-type. A highly transparent grid represents the front contact. The front glass plate through which the incoming radiation penetrates to the junction provides a hermetically sealed encapsulation which is required for long time stability. 

A general tendency similar to that of oxygen deficient oxides applies to metal deficient oxides in the oxide Mi-yO the metal vacancies are doubly charged at very small deviations from stoichiometry and tend to become singly charged with increasing nonstoichiometry. 

Modulation superimposed on the component layers will substantially influence the interlayer match and sometimes cause deviations from the simple situations described above. It may be of a chemical nature, i.e. ordered substitutions or ordered metal vacancies, but sometimes also geometrical a wave-like modulation or corrugation as a result of the chemical variations. Such modulations are apparently the reason for the small deviations between the respective T and H subcell axes in the majority of cylmdrites of the deviations of the subcell axes in Phase away... 

Diffusion in NijAl has been studied by few investigators - in particular Chou and Chou (1985) and Hoshino et al. (1988) -and has been reviewed and discussed with respect to mechanisms and defects (Bakker, 1984 Wever et al., 1989 Stoloff, 1989). The constitutional defects are antistructure atoms on both sides of stoichiometry, i.e. Al on Ni sites and Ni on Al sites, and the concentration of constitutional, i.e. ather-mal, vacancies is very small. The vacancy content of 6 x 10 at the melting temperature and the vacancy formation enthalpy of 1.60 eV correspond to the respective values for Ni, i.e. the vacancy behavior of NijAI is similar to that of pure metals (Schaefer et al., 1992). The diffusion of Ni in NijAl is not very different from that in pure Ni and at high temperatures it is insensitive to deviations from stoichiometry. The diffusion of Al in NijAl is less well studied because a tracer is not readily available. Defects may interact with dissolved third elements which affects diffusion. In particular vacancies interact with B which is needed for ductilization , and this leads to a complex dependence of the Ni diffusion coefficient on the Al and B content of NijAl (Hoshino etal., 1988). Data for the diffusion of the third elements, Co, Cr, or Ti, in Nij Al are available (Minamino etal., 1992). 

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