Ions, order

The Orientation of Water Molecules Adjacent to an Ion. Order and Disorder in the Vicinity of Solute Particles. Coulomb Attraction and Repulsion between Ions. Activity Coefficients. The Distance of Closest Approach. Activity Coefficients of Various Solutes. Forces Superimposed on the Coulomb Forces. 

The ideal composition of Prussian blue is Fe(III)4[Fe(II)(CN)g]3.15H2O. The crystal structure is cubic. All Fe(III) lattice sites are occupied, whereas those of Fe(II) are only 75% occupied. At low temperatures the paramagnetic Fe(III) ions order ferromagnetically (T = 5.6 K). Finally we note that upon replacing Fe(II) by Ru(II) or Os(II) the color properties are not drastically influenced. 

The first half of this chapter concentrates on the mechanisms of ion conduction. A basic model of ion transport is presented which contains the essential features necessary to describe conduction in the different classes of solid electrolyte. The model is based on the isolated hopping of the mobile ions in addition, brief mention is made of the influence of ion interactions between both the mobile ions and the immobile ions of the solid lattice (ion hopping) and between different mobile ions. The latter leads to either ion ordering or the formation of a more dynamic structure, the ion atmosphere. It is likely that in solid electrolytes, such ion interactions and cooperative ion movements are important and must be taken into account if a quantitative description of ionic conductivity is to be attempted. In this chapter, the emphasis is on presenting the basic elements of ion transport and comparing ionic conductivity in different classes of solid electrolyte which possess different gross structural features. Refinements of the basic model presented here are then described in Chapter 3. 

Figure 18. Schematic representation of several possible types of solid solution. Shaded and blank layers represent expanding and mica-like units (2 1 structures). Solid and unfilled circles represent two species of interlayer ions, a totally random in all aspects b = interlayer ion ordering, single phase montmorillonite c = ordered interlayer ions which result in a two-phase mica structure, two phases present d = randomly interstratified mineral, one phase e = regular interstratification of the 2 1 layers giving an ordered mixed layered mineral, one phase present f = ordered mixed layered mineral in both the interlayer ion sites and the 2 1 interlayering. This would probably be called a single phase mineral.

The mixed-metal oxide spinel, MgA fTt, is one of the most important inorganic materials. The structure of spinel can be regarded as a ccp structure of O2-anions with Mg2+ ions orderly occupying /8 of the tetrahedral interstices, and Al3+ ions orderly occupying half of the octahedral interstices the remainder 7/x tetrahedral interstices and half octahedral interstices are unoccupied. The sites of the three kinds of ions in the face-centered cubic unit cell are displayed in Fig. 9.6.29. 

Each Ca2+ is thus twelve-coordinated and each Ti4+ six-coordinated by oxygen neighbors, while each O2- is linked to four Ca2+ and two Ti4+ ions. As expected, it is the larger metal ion that occupies the site of higher coordination. Geometrically the structure can be regarded as a ccp of (O2- and Ca2+) ions, with the Ti4+ ions orderly occupying of the octahedral interstices. 

Mn + ions per introduced vacancy. In fact, a modest MR effect is seen for x = 0.06 and 0.11 As well, a usual charge ordering is reported for the x = 0.11 phase, which is required to explain the neutron diffraction data in the magnetically ordered state. Here layers of Mn + ions order in every fourth layer in the G-type magnetic structure known for CaMnOs (see Figure 25). ... 

Figure 2.5 Creating the bond graph for CaCrF5 (a) ions ordered by bonding strength (given in parentheses), (b) after the formation of the CrF3- complex, bond valences shown on the bonds, (c) the complete predicted bond graph, (d) bond graph observed for the monoclinic structure with the predicted bond valences.

The different magnetic behaviour of Eu and Eu ions is clearly seen in EU3O4 [36]. This oxide becomes antiferromagnetic below 6-2 K. Above the Neel temperature there are two peaks with chemical isomer shifts of -f 0-6 mm s (Eu +) and —12-5 mm s (Eu +). In the magnetic phase only the Eu " " ions order, with a field at 1-2 K of 305 kG. The temperature dependence... 

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