Plane oxygen

Figure 6.10 (Continued) (c) conduction plane and the two adjacent oxygen planes. The...

Both sepiolite and palygorskite contain tetrahedral silicate sheets (with a variety of substitutions for the Si " ), but the apicies of the tetrahedra are thought to point up or down with the transition areas containing Ca and Mg ions, and bound or associated H2O. The arrangement produces a continuous basal oxygen plane that is compartmentalized. Laths or ribbons three chains wide in sepiolite and two chains wide in palygorskite are separated by discontinuous octahedral areas (Fig. 2.16A and B). 

The conformation of the ligand differs from that in the sodium complex. The change is mainly in the torsion angles about two carbon-oxygen bonds, corresponding to a displacement of two alkyl carbon atoms, so that these are all on one side of the oxygen plane in the potassium complex. 

Figure 18 The spinel (MgAl204) structure. Tetrahedral and octahedral polyhedra are depicted by the dotted lines. Not all the atoms are shown for reasons of clarity. Note the oxygen planes along the 111 direction of the unit ceil.

FIGURE 10.8 The structure of 1-2-3 (a) the metal positions (c) idealized structure of YBa2Cu307-T (d) the extended structure of YBa2Cu307, depicting copper-oxygen planes, with the copper-oxygen diamonds in between. Key Cu, blue Ba, green Y, aqua 0, red. 

The 1-2-3 superconductor has a perovskile-like structure (7.33a,c). There are systematic oxygen atom vacancies in the unit cell compared to a stack of simple perovskite unit cell (Fig. 7.33b). These occur between adjacent copper atoms in the chains along the c axis. The vacancies are in the yttrium atom plane. There are also vacancies between copper atoms along the a axis in the copper-and-oxygen planes... 

We have reported a large anisotropy in the critical current density Jc of high quality YBa2Cu307.3 thin films. A large enhancement of Jc when the applied magnetic field H is precisely parallel to the Cooper-Oxygen planes of the lattice was observed. 

K is obtained from associated K-feldspars and micas. The layer charge is increased by the reduction of iron in the octahedral sheet and incorporation of Al, entering through the ditrigonal holes in the basal oxygen plane, into the tetrahedral sheets (Weaver and Beck, 1971a Pollard, 1971). Weaver and Beck have presented evidence that indicates mixed-layer clays formed in this manner contain 20—30% chloritic layers and are actually mixed-layer illite-chlorite-montmorillonite clays. 

Electron micrograph of copper-oxygen planes in a sample of superconducting yttrium-barium-copper-oxide. Planes are well-defined up to the grain boundary. Photo courtesy of Argonne National Laboratory.)... 

Bulk sapphire has rhombohedral symmetry, which is usually treated as hexagonal (space group R3c), with 30 atoms (six AI2O3 units) per primitive unit cell. The lattice parameters (a=fe=4.7570 A, c=12.9877 A) and the internal coordinates (x=0.3063, z=0.3522) are taken from ref. [56]. The bulk unit cell consists of an alternated stacking, along the c-axis, of two Al planes (twelve in the unit cell) with one atom per plane, and one oxygen plane (six in the unit cell) with three O ions arranged with a threefold symmetry. 

CoO, MnO and NiO could a priori be expected to have very similar behaviours. Indeed, they share the same strueture and nearly the same lattice parameter (acube(NiO)=4.17 A, acube(CoO)=4.26A and acube(MnO)=4.44A). In addition, the atoms in the (111) pure Co, Ni or Mn planes are spin uncompensated i.e. the individual cation (111) ferromagnetic planes have a mesh with a net magnetic moment [102, 103]. The AF ordering is along the [111] direction, exchange-moderated by the pure oxygen planes [104]. The Neel... 

The oxides of iron are of broad interest because of their importance in such diverse fields as corrosion, catalysis, geochemistry and magnetism. Despite their different structures and metal oxidation states, the oxides of iron — FeO, Fe304, and a- and y-Fe203 - have in common a close-packed plane of oxygen anions in the (111) orientation in which the nearest-neighbor distances are rather similar (within 5%). The various phases differ in the distribution of Fe within the cation planes that lay between the oxygen planes. FeO is rocksalt, whereas... 

---