Structure and Ionic Motion

Much success in determining crystal structures has been achieved through high-quality powder X-ray data of polycrystalline powders [57]. Structures which have been elucidated include P(EO)3LiCFj SO, P(E0),NaClO4, P(EO),KSCN, P(EO)4RbSCN,P(EO)4NH4SCN, and P EO),LiN(SO,CF,)2[18,58]. All crys- 

Many features are common to all polymer electrolytes. The helical conformation 

have recently identified the anion as essentially a 

Many features are common to aU polymer electrolytes. The hehcal conformation of PEO is retained, but with a different pitch. Each turn of the helix contains one cation coordinated by oxygen atoms from the polymer chain. The number of coordinating ether oxygens per cation increases from 3 (11 ) to 5 (Rb ). Each 

2 Solvent-Free Polymer Electrolytes 637 (c) Intrachain movement via ion cluster 

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Kumar, P.P. and Yashonath, S. (2002) Structure, conductivity, and ionic motion in Nai+jZr2SijP3 jOi2 A simulation study. J. Phys. Chem. B, 106, 7081-9. 

Molten Salts. - The molecular structure and rotational motion of the ionic liquid l-butyl-3-methylimidazolium hexafluorophosphate ([BMIMJPFe]) were studied over a wide temperature range using the Bloembergen-Purcell-Pound... 

In other cases, discussed below, the lowest electron-pair-bond structure and the lowest ionic-bond structure do not have the same multiplicity, so that (when the interaction of electron spin and orbital motion is neglected) these two states cannot be combined, and a knowledge of the multiplicity of the normal state of the molecule or complex ion permits a definite statement as to the bond type to be made. 

The cathode of a battery or fuel cell must allow good ionic conductivity for the ions arriving from the electrolyte and allow for electron conduction to any interconnects between cells and to external leads. In addition these properties must persist under oxidizing conditions. An important strategy has been to employ layered structure solids in which rapid ionic motion occurs between the layers while electronic conductivity is mainly a function of the layers themselves. 

There are two classes of materials which may be used as electrolytes in all-solid-state cells polymer electrolytes, materials in which metal salts are dissolved in high molar mass coordinating macromolecules or are incorporated in a polymer gel, and ceramic crystalline or vitreous phases which have an electrical conductance wholly due to ionic motion within a lattice structure. The former were described in Chapter 7 in this... 

Like infrared spectrometry, Raman spectrometry is a method of determining modes of molecular motion, especially the vibrations, and their use in analysis is based on the specificity of these vibrations. The methods are predominantly applicable to die qualitative and quantitative analysis of covalently bonded molecules rather than to ionic structures. Nevertheless, they can give information about the lattice structure of ionic molecules in the crystalline state and about the internal covalent structure of complex ions and the ligand structure of coordination compounds both in the solid state and in solution. 

This intermolecular potential for ADN ionic crystal has further been developed to describe the lowest phase of ammonium nitrate (phase V) [150]. The intermolecular potential contains similar potential terms as for the ADN crystal. This potential was extended to include intramolecular potential terms for bond stretches, bond bending and torsional motions. The corresponding set of force constants used in the intramolecular part of the potential was parameterized based on the ab initio calculated vibrational frequencies of the isolated ammonium and nitrate ions. The temperature dependence of the structural parameters indicate that experimental unit cell dimensions can be well reproduced, with little translational and rotational disorder of the ions in the crystal over the temperature range 4.2-250 K. Moreover, the anisotropic expansion of the lattice dimensions, predominantly along a and b axes were also found in agreement with experimental data. These were interpreted as being due to the out-of-plane motions of the nitrate ions which are positions perpendicular on both these axes. 

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