Oxygen layered structures

The structural relationships in Bi203 are more complex. At room temperature the stable fonn is monoclinic o -Bi203 which has a polymeric layer structure featuring distorted, 5-coordinate Bi in pseudo-octahedral iBiOs units. Above 717°C this transforms to the cubic -form which has a defect fluorite structure (Cap2, p. 118) with randomly distributed oxygen vacancies, i.e. [Bi203D]. The )3-form and several oxygen-rich forms (in which some of the vacant sites are filled... 

Ni, Mn, V). In the ideal layered LiM02 structure, the Li+ and the M3+ ions occupy octahedral sites in alternate layers between cubic close packed oxygen layers (Fig. 5). 

Droit s original 4 1 5 phase has been studied by X-ray diffraction (Nowacki Silverman, 1961, 1962) and found to have a rhombohedral layer structure. The 1 1 1 phase was also found to have a layer structure, which consisted of pseudohexagonal layers of zinc atoms separated by ordered layers comprising oxygen and chlorine atoms (Feitknecht, Ostwald Forsberg, 1959). This fundamental structure was apparently found for both of the crystalline modifications in which this phase has been found to occur, namely the monoclinic and the orthorhombic (Sorrell, 1977). 

Figure 4.17 Structure of the intercalation phase LixCo02 (a) packing of the oxygen layers in C0O2 before intercalation is hexagonal closest packing and (b) after intercalation the packing changes to cubic closest packing.

The unit cell of (3-alumina is hexagonal, with lattice parameters a = 0.595 nm, c = 2.249 nm. The dominant features of the idealized structure of (3-alumina, with composition NaAlnOi7, are layers called spinel blocks stacked perpendicular to the c axis (Fig. 6.10a). These blocks are composed of four oxygen layers in a... 

Figure 8.14 Layer structure of oxides with composition Lii-yNii+yCU (a) Nii.o202, with the oxygen atoms in hexagonal... ABAB. .. sequence and (b) nominal compositions between Lio.o7Ni02-Lii.oNi02 have the oxygen atoms in cubic. .. ABCABC... sequence.

An example of a layer structure mixed conductor is provided by the cathode material L CoC used in lithium batteries. In this solid the ionic conductivity component is due to the migration of Li+ ions between sheets of electronically conducting C0O2. The production of a successful mixed conductor by doping can be illustrated by the oxide Cei-jPxx02- Reduction of this solid produces oxygen vacancies and Pr3+ ions. The electronic conductivity mechanism in these oxides is believed to be by way of electron hopping between Pr4+ and Pr3+, and the ionic conductivity is essentially vacancy diffusion of O2- ions. 

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