Kagome net

Nickel atoms in BajNi B form distorted, puckered 3.6.3.6-kagome nets stacked in six layers perpendicular to the c axis. The densely packed framework of trigonal-Ni prisms again result in boron-pair formation, although Ba atoms are too large to be sandwiched between two Ni layers, and only four Ba can be accommodated within six Ni layers. Superconductivity is found for ( a, Sr, Ba)2pt9Bg borides with a structure related to Ba2Ni9Bfi and e o,B2 however, with respect to crystal chemistry and boron coordination, only the subcell is derived so far. 

Figure 8.1 Two types of Kagome nets that form the basis of the o—phase crystal structure. A—net with shared corners. B—net with shared edges.

Figure 3.25. Stacking symbols applicable to larger unit cells. A, B, C three nodes in the unit cell of a triangular net a, b, c six nodes of a hexagonal net in the unit cell a, 3, p nine nodes of a kagome net in the unit cell. The coordinate doublets are indicated.

Figure 29 (a) Kagome net formed by [M Fe] (bright) and [M "Fg] (dark) octahedra (b) O-I weberite structure of Na2NiAlp7. View along the M" octahedral chains, Na grey spheres... 

Pyrochlore- and RbNiCrFg-Type Structures. Closely related to the weberite variants are pyrochlores AA M2Fv (A = Na, A = Ca, Cd M = Mg, Co, Ni, Cu, Zn). Here, all octahedra are equivalent and the cubic 3D network can be described as intersecting systems of Kagome nets with planes parallel to the faces of a tetrahedron. Another approach is the description as cross-linked octahedral chains where at the crossing points typical tetrahedra of comer-connected octahedra are generated (Figure 31). 

The first structure (shown in Fig. 4b) consisted of a presumably pure Pt Kagome net terminating layer. The close packing directions of the surface... 

Symbols of structure types which may be considered as sequences of 2-dimensional hexagonal nets can be partly derived from those of cubic structure types, if the nets are arranged perpendicular [111]. According to Hermaim a hexagonal closed packed layer may be symbolised by H, a graphite layer by G, and a Kagome net by N. 

Figi 12. A hexagonal closed packet net upper left) and two blittings in a graphite layer G (upper-right) and a Kagome net N lower left). 

Pearson (1984) noticed that the ThMni2 structure contains two interpenetrating kagome nets of Mn atoms that lie in the (100) and (010) planes. The nets are not planar since atoms located in the 8(i) and 8(j) positions have x-parameters of 0.275-0.284 (see table 2 for the uranium aluminides and the RFeioV2 compounds) instead of 0.250 for the ideal planar case. 

Figure 2.15 The DC magnetic susceptibility of KFe3 S04)2(0H)g with full occupation of the kagome net by Fe. Note the zero field cooled (ZFC)/field cooled (FC) divergence below Tn = 65.5 Reprinted with permission from Grohol et ai, 2003 [35]. Copyright (2003) American Physical Society...

Figure 2.19 The structure of kapellasite, a second form of ZnCu3(OH)6Cl2. The colouring scheme is the same as that for Figure 2.18 (herbertsmithite) except that the H atoms are shown as very small spheres. Note that the Zn and Cu octahedra are accommodated within the same layer by edge-sharing and that the layers are now connected only by Cl-H-O hydrogen bonds.The Cu sites form a perfect kagome net as in Herbertsmithite...

Figure 2.24 The langesite structure, Nd(Pr)3Ga5SiOi4. The Nd(Pr) square antiprismatic sites are dark grey, the Ga octahedral and tetrahedral sites are light grey. The Si atom is a small sphere. The distorted kagome net of Nd(Pr) ions is shown on the right...

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