Cubic structure space group

Another contribution is represented by an investigation of a cubic thallium cluster phase of the Bergmann type Na13(TlA.Cdi A.)27 (0.24 < x <0.33) (Li and Corbett 2004). For this phase too the body centred cubic structure (space group Im 3, a = 1587-1599 pm) may be described in terms of multiple endo-hedral concentric shells of atoms around the cell positions 0, 0, 0, and 14,14,14. The subsequent shells in every unit are an icosahedron (formed by mixed Cd-Tl atoms), a pentagonal dodecahedron (20 Na atoms), a larger icosahedron (12 Cd atoms) these are surrounded by a truncated icosahedron (60 mixed Cd-Tl atoms) and then by a 24 vertices Na polyhedron. Every atom in the last two shells is shared with those of like shells in adjacent units. A view of the unit cell is shown in Fig. 4.38. According to Li and Corbett (2004), it may be described as an electron-poor Zintl phase. A systematic description of condensed metal clusters was reported by Simon (1981). 

Table 1. Cubic structure (space group Fm- im) of the PbS thin film deposited at 293 K a = 0.59395 nm.

There are two types of spinel, normal and inverted. Normal spinels have all the A ions in tetrahedral sites and all B ions in octahedral coordination. When the structures are inverted, the divalent A ions and half of the trivalent B ions are in the octahedral sites while the remaining B ions have tetrahedral coordination. Both normal and inverted spinels have the same cubic structure (space group Fd3m). 

Figure 19. Crystal structure of W3pe3C. In the middle of the drawing all atoms of this cubic structure (space group Fd3m) are shown. The carbon-filled octahedra of tungsten atoms are emphasized on the left-hand side, only the condensed Fe4 tetrahedra are drawn on the right-hand side of the figure.

A different ordering pattern in the phases K CaUjO and K SrUjOjj leads to the cubic structures space group Im3m (229), a=0.8483nm (Ca ) and a=0.8582nm (Sr ). In these latter phases the U cation shares the octahedral B-sites with Ca or Sr. ... 

Diamond is an allotropic form of the element carbon with cubic structure (space group O -FcOm) which is thermodynamically stable at pressures above 6GPa at room temperature and metastable at atmospheric pressure. At low pressures diamond converts rapidly to graphite at temperatures above 1900 K in an inert atmosphere. The chemical bonding between the carbon atoms is covalent with sp hybridization. 

Both CU7 38Mn4Sni2S32 (Z = l) and CU7 07Ni4Sni2S32 (Z = l) crystallize in the cubic Fd3m space group with a= 10.4145 and 10.305(1) A respectively. The occupancies of M and Sn (which occupy the 16d sites) refine to 0.25 and 0.75 and hence were fixed in the final refinement. However in both the structures a small amount of Cu deficiency was observed in the 8 a sites. The interatomic distances in both the compounds are in accordance with the earher known compounds [17]. The ionic radii of Mn (VI, HS) is 0.83 and is larger than the size of the Ni (Vl) which is 0.69 [22]. Accordingly the Mn/Sn-S bond distance is greater than the Ni/Sn-S bond distance. 

Note 5 Two BPs of different cubic symmetry (space group I 4i32 for BP I and P 4i32 for BP II) are presently known, together with a third (BPIII) of amorphous structure. Several other BPs of different cubic symmetry exist but only in the presence of external electric fields. 

The sodium chloride structure, AX systems. Cubic Fm3m (Space Group 225) The sodium chloride or rock salt, NaCl, structure has a simple face-centered cubic unit cell (Figure 8) with alternating cations-anions along the three cubic axes. 

The Perovskite Structure, ABXS Systems. Cubic Pm3m (Space Group 221) A cubic structure was assigned to the mineral perovskite, CaTiOj, but this particular compound was later found to actually possess orthorhombic symmetry. Today, however, we refer to the perovskite structure in its idealized form as having cubic symmetry and it is normally represented by a simple unit cell (Figure 10). 

Fulleride K3C60 is a face-centered cubic crystal, space group Fm3m, with a = 1424(1) pm and Z = 4. The C603- ions form a ccp structure with K+ ions filling all the tetrahedral interstices (radius 112 pm) and octahedral interstices (radius 206 pm), as shown in Fig. 14.2.8. 

For example, the family of perovskite minerals and high-temperature ceramic superconductors exhibits this descent of symmetry, from the cubic "ideal" perovskite structure (space group Pm3m, the real mineral perovskite is orthorhombic, space group Pnma, with a fourfold larger unit cell than the ideal cubic one) to orthorhombic structures for the highest-critical... 

List the point coordinates, relative to the origin (0, 0, 0), for all the atoms in the unit ceii of a pure metal with the body-centered cubic (BCC) structure (space group Im 3 m). The unit cell contains two atoms. There is one-eighth of an atom at each corner of a cube (each corner atom is shared by eight unit cells) and another atom of the same kind at the center of the cube (wholly owned by one unit cell). 

Consider a pure metal with the cubic-closed packed (CCP) structure (space group Fm 3 m). In this structure, there is an atom at each corner of a cube and an atom at the center of each of the cube s six faces. How many atoms are there in the unit cell Which point could be chosen as the origin What are the point-coordinates of all the atoms, relative to the origin Is the origin on a special position What is the multiplicity of the origin ... 

Compared to lithium and sodium borohydride, potassium borohydride has the highest hydrogen desorption temperature of 584 °C and melting temperature of 607 °C [25]. The hydrogen content is 7.7 wt.%. Potassium borohydride crystallizes in the cubic NaCl-type structure (space group Fm3m) as do sodium, rubidium, and caesium borohydrides. [BH4] units are octahedrally coordinated by K atoms. 

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