Rhombohedral unit cells, 421 table

R = rhombohedral (unit cell can be primitive or nonprimitive see notes to Table 1-11) Principal axis of ration given number n = order e.g., 2 = twofold axis of rotation... 

Potassium hexafluoroplatinate(v), which is best made by the interaction of dioxygenyl hexafluoroplatinate(v) with potassium fluoride in iodine pentafluoride, is isomorphous with the analogues of the other platinum metals and is nearly isodimensional with potassium hexafluororuthenate(v). The rhombohedral unit-cell dimensions and volume for the platinum metal salts KM Fg are given in Table 2. 

The Fluorination of Platinum in the Presence of Powdered Glass.—Fluorine, diluted with nitrogen, was passed in a slow stream over a heated mixture of powdered glass and platinum at 400° and a mixture of pale brown and black particles was left. J -Ray powder photographs showed these particles were two phases. A simple pattern, characteristic of the black material, was indexed on the basis of a rhombohedral unit-cell, a = 5-39 i 0 02 A, a = 54-7 i 0-2°, / = 97 A. Observed and calculated Ijd" values are in Table 3. The complex pattern of the light brown phase was identical with that of platinum oxide trifluoride. 

Properties of Potassium Hexafluoroplatinately).—This salt is mustard yellow. A sample containing some iodine, possibly as iodyl fluoride, was paramagnetic. The low value of the magnetic moment, p = 0-87 B.M. (at 23°), may, in part at least, be due to this impurity. An infrared spectrum, of a Nujol mull, recorded with sodium chloride and cmsium bromide optics, showed two broad, overlapping, absorption bands, with peaks at 590 and 640 cm.. X-Ray powder photographs of the salt have been indexed on the basis of a rhombohedral unit-cell, a = 4-96 A, a = 97-4°, U = 119 9 A. The observed and calculated values for 1/df are given in Table 5. The solid can be stored indefinitely in well-dried, sealed tubes but decomposes... 

Both samples gave the same X-ray powder pattern which was indexed on the basis of a primitive rhombohedral unit cell (see Table III). The Raman spectrum is shown in Figure 1 (6) and is summarized in Table II. The solid can be stored indefinitely at dry ice temperature but is not stable at room temperature and liquifies and dissociates into its components within a few days. Although the dissociation pressure of the material was less than 5 Torr at 20°C it slowly volatilized under dynamic vacuum. 

Table IX. X-ray Powder Daia (Cu Ka Radiaiion, LiF Monochromaior) for RuFj with a Rhombohedral Unit Cell ...

X-ray powder diffraction data for the compounds Sr3Sc(B03)3 and SreYj 07AIq,93(803)6 are given in Table I. Rhombohedral unit-cell parameters for each compound prepared by the two different synthetic methods are listed in Table II. Cell parameters were determined by least-squares analysis of 10 reflections collected by using an automated Philips powder diffractometer and corrected with NIST Si standard 640b. The nonstoichiometry of the Y-Al phase has been verified by single-crystal X-ray analysis. Powder diffraction measurements indicate that it is a line phase at this stoichiometry. 

The materials for solid solutions of transition elements in j3-rh boron are prepared by arc melting the component elements or by solid-state diffusion of the metal into /3-rhombohedral (/3-rh) boron. Compositions as determined by erystal structure and electron microprobe analyses together with the unit cell dimensions are given in Table 1. The volume of the unit cell (V ) increases when the solid solution is formed. As illustrated in Fig. 1, V increases nearly linearly with metal content for the solid solution of Cu in /3-rh boron. In addition to the elements listed in Table 1, the expansion of the unit cell exceeds 7.0 X 10 pm for saturated solid solutions " of Ti, V, (2o, Ni, As, Se and Hf in /3-rh boron, whereas the increase is smaller for the remaining elements. The solubility of these elements does not exceed a few tenths at %. The microhardness of the solid solution increases with V . Boron is a brittle material, indicating the accommodation of transition-element atoms in the -rh boron structure is associated with an increase in the cohesion energy of the solid. 

Lattice parameters of Sm2Fel A.Co c)17C3, with various x and y values are listd in Table 10.2. The XRD lines observed on all the Sm2(Fe, xCox) 7Cy compounds were completely assignable to the Th2Zn]7-type crystal lattice of rhombohedral symmetry (space group = R3m), and the lattice parameters were in good agreement with reported values.3,35 The unit cell volume decreased with the concentration of Co but increased with the carbon content. This indicates that carbon atoms share the interstitial 9e sites.36... 

X-ray powder patterns were obtained for the three Pr(IV) compounds. For NaTPreFgi, a rhombohedral (R3) structure was found, isostructural with NaTUeFgi. Na2PrFe was found to be isostructural with orthorhombic y-Na2UF6 (Immm). The material identified as PrF4 was found to be isostructural with monoclinic UF4 (C2/c). The derived lattice parameters and unit cell volumes are given in Table I. 

Table 2. Trigonal Unit Cells for the Rhombohedral (R3) LiMF(i Salts of the Second and Third Transition Series ...

Any of the fourteen Bravais lattices may be referred to a primitive unit cell. For example, the face-centered cubic lattice shown in Fig. 2-7 may be referred to the primitive cell indicated by dashed lines. The latter cell is rhombohedral, its axial angle a is 60°, and each of its axes is l/ /2 times the length of the axes of the cubic cell. Each cubic cell has four lattice points associated with it, each rhombohedral cell has one, and the former has, correspondingly, four times the volume of the latter. Nevertheless, it is usually more convenient to use the cubic cell rather than the rhombohedral one because the former immediately suggests the cubic symmetry which the lattice actually possesses. Similarly, the other centered nonprimitive cells listed in Table 2-1 are preferred to the primitive cells possible in their respective lattices. 

Further information on the rhombohedral-hexagonal relationship and on unit cell transformations in general may be obtained from the International Tables for X-Ray Crystallography [G.l l], Vol. 1, pp. 15-21. 

Table 11. Unit cell dimensions for materials without a refined structure, angle refers to tx for rhombohedral crystals and p for monoclinic crystals...

Room-temperature-stable jS-NaNa is rhombohedral, space group [66], with one formula unit per primitive unit cell so that structurally it is among the simplest of the metal azides. This has made NaNa the logical starting material for lattice-dynamic studies of inorganic azides. Unfortunately, single crystals of sufficient size for CNIS studies have not been grown, so dispersion-curve measurements have not been performed. Nevertheless, the lattice dynamics are partially determined as summarized in Table V. 

Fig.8 A Large scale and B high-resolution image of 11b on Au(lll)-(1 x l)/0.05 M H2SO4 in the presence of 3 mM TMA, Es = 0.03 V, ii = 150 pA. The characteristic quadratic and rhombohedral structure elements as well as the primitive imit cell are indicated. C Proposed packing model of TMA in Ilb. The parameters of the unit cell are summarized in Table 1 [67]...

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