Misfit region

Structure breaker ions bind water molecules around them sufficiently to cause a mismatch between the structure of the bound water and that of unmodified water typical of the pure solvent. But the order induced is not great enough to outweigh the disorder created in the misfit region, and this will occur with the less strongly polarising ions such as Rb, ... 

When the entropy contributions from (i) and (ii) are added up and subtracted from the entropies of hydration, there is a finite value left which is assigned as a change of entropy consequent on the dismption of the water stmcture in the misfit region, often labelled... 

If the decrease in volume is greater than expected, then the ion is a stmcture-maker - constriction of the solvent in the bound shell more than outweighs the effect of the misfit region. 

Fig. 1.5 A bubble raft illustrating the nature of a dislocation. The region of misfit near Y can be seen. (After Bragg and Nye )...

As remarked in the previous section, single crystals are not perfect but are built of domains of material that are slightly mismatched. The interfaces between these regions are called low-angle or small-angle grain boundaries. These boundaries consist of an array of dislocations arranged so as to remove the misfit between the... 

A > 0, i.e. repulsive walls. The number of walls tends to be as small as possible, i.e. a striped network of parallel walls (SI) will be formed in the incommensurate region. The C-SI transition should be continuous. The striped phase is expected to be stable only close to the C-I transition. At larger misfits the hexagonal symmetry should be recovered in a first-order SI-HI transition. 

Erom the preceding discussion, the distinction between misfit defects shear domains formed by pure shear and CS planes formed by the elimination of anion vacancies in a specific crystallographic plane by shear and the collapse of the oxide lattice on that plane can be understood. This distinction between defects is central to catalytic reaction mechanisms in oxides. However, it is often not made in the literature on oxide catalysis and solid state oxide chemistry. This can result in an incorrect interpretation of observed data and of the role played by lattice oxygen atoms in catalytic reactions. The former are regions containing... 

Ultrathin films of hexagonal symmetry under compressive strains (e.g. Ag/Pt(lll) with a misfit of +4.3%) relax the strain in a similar way by forming striped-phases. The domain walls are now regions of locally lower atomic density and are imaged dark in STM [73]. The stable configuration, however, consists of a trigonal network of crossed domain walls. 

Figure 5 Contours of r.m.s misfit (%) to seismological reference model akl35 of density (red) and bulk sound velocity (green) for candidate lower-mantle compositions, parametrized in terms of Mg/(Mg -f Fe) (= Xmj) and Si/(Mg -f Fe)(= Xpv), over the entirety of the lower mantle. Shaded region at Xpv > 1 indicates free silica. Triangle denotes pyrolite. Plus signs denote minima of r.m.s. misfit. Root of lower-mantle adiabat is 2,000 K at 660 km depth.

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