Solid solution structure

A solid solution is a crystal structure in which two (or more) atom types are arranged at random over the sites normally occupied by one atom type alone. For example, in the comndum structure solid solution formed by Cr2C>3 and AI2O3, a random mixture of Cr3+ and Al3+ ions occupy the cation sites that are only occupied by one of these in the parent phases. The formula of the solid solution materials is written (Al i JCCrJC)203. In this example, x can vary continuously between 0 and 1.0. In some cases, especially when the atoms involved have different sizes, only partial solid solutions are found, characterized by a composition range in which the span of x is smaller than 1.0. Solid solutions are widely exploited as both the chemical and physical properties of the solid can be varied sensitively by changing the relative amounts of the components of the solid solution. 

Other multiphase ceramics. Numerous multiphase ceramic formulations for conditioning of various wastes have been designed (Harker 1988). These so-called tailored ceramics were developed for immobilization of complex defence wastes at the Savannah River Plant and Rockwell Hanford Operation (Harker 1988). Tailored ceramics include ACT and REE hosts (fluorite-structure solid solutions, zirconolite. 

The influence of geometrical considerations is similarly reflected in the common occurrence of solid solution among compounds with the perovskite, ilmenite and spinel structures, to which we have already referred. In these structures solid solution takes place particularly readily because in each case the structure is basically a rigid framework of large ions with small cations accommodated in the interstices. So long... 

Direct incorporation into the lattice structure (solid-solution formation) and surface adsorption. 

Lee JH, Yashima M, Yoshimura M (1998) Ionic conductivity of fluorite-structured solid solution Yo.8Nbo.2O17. Sohd State Ionics 107 47-51... 

Defect and disordered structures, solid solutions Candidates for physical properties... 

Solid solution Solid in which components are compatible and form a unique phase of mixed composition often used to denote the compatibility of two similar components in one crystal structure. Solid solutions occur commonly in cement hydrates (and clinkers), e.g. in C-S-H (calcium-silicate-hydrate), AFm and AFt phases. 

Metals A and B form an alloy or solid solution. To take a hypothetical case, suppose that the structure is simple cubic, so that each interior atom has six nearest neighbors and each surface atom has five. A particular alloy has a bulk mole fraction XA = 0.50, the side of the unit cell is 4.0 A, and the energies of vaporization Ea and Eb are 30 and 35 kcal/mol for the respective pure metals. The A—A bond energy is aa and the B—B bond energy is bb assume that ab = j( aa + bb)- Calculate the surface energy as a function of surface composition. What should the surface composition be at 0 K In what direction should it change on heaf)pg, and why ... 

There is a large volume of contemporary literature dealing with the structure and chemical properties of species adsorbed at the solid-solution interface, making use of various spectroscopic and laser excitation techniques. Much of it is phenomenologically oriented and does not contribute in any clear way to the surface chemistry of the system included are many studies aimed at the eventual achievement of solar energy conversion. What follows here is a summary of a small fraction of this literature, consisting of references which are representative and which also yield some specific information about the adsorbed state. 

An effect which is frequently encountered in oxide catalysts is that of promoters on the activity. An example of this is the small addition of lidrium oxide, Li20 which promotes, or increases, the catalytic activity of dre alkaline earth oxide BaO. Although little is known about the exact role of lithium on the surface structure of BaO, it would seem plausible that this effect is due to the introduction of more oxygen vacancies on the surface. This effect is well known in the chemistry of solid oxides. For example, the addition of lithium oxide to nickel oxide, in which a solid solution is formed, causes an increase in the concentration of dre major point defect which is the Ni + ion. Since the valency of dre cation in dre alkaline earth oxides can only take the value two the incorporation of lithium oxide in solid solution can only lead to oxygen vacaircy formation. Schematic equations for the two processes are... 

Fig. 7.7. Solid-solution structures. In interstitial solutions small atoms fit into the spaces between large atoms. In substitutional solutions similarly sized atoms replace one another. If A-A, A-B and B-B bonds hove the some strength then this replacement is random. But unequal bond strengths con give clustering or ordering.

Eqn(3) allows a direct determination of LRO-parameter from resistivity measurement by using the constant A as a fit parameter. Eqn(l) is of more complicated character, where besides the SRO-parameters in the different coordination spheres there enter details of the band structure (Y,) which influence sign and magnitude of resistivity variation with degree of SRO. However, restricting to nearest neighbours and using an adequate model for the dependence of a on temperature and concentration, reliable SRO-parameters have been deduced from resistivity measurement for several solid solutions. ... 

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