Orthorhombic unit cell, 421 table

Fiber patterns. In vacuum, the stretched and annealed glucan film made from [. salivarius (sample B) gave a clear x-ray pattern as shown in Figure 1 (17). All 29 reflections (Figure 2) can be indexed with an orthorhombic unit cell (Tables I and II). In the previous report (17), the unit cell was reported to be... 

The many commercially attractive properties of acetal resins are due in large part to the inherent high crystallinity of the base polymers. Values reported for percentage crystallinity (x ray, density) range from 60 to 77%. The lower values are typical of copolymer. Poly oxymethylene most commonly crystallizes in a hexagonal unit cell (9) with the polymer chains in a 9/5 helix (10,11). An orthorhombic unit cell has also been reported (9). The oxyethylene units in copolymers of trioxane and ethylene oxide can be incorporated in the crystal lattice (12). The nominal value of the melting point of homopolymer is 175°C, that of the copolymer is 165°C. Other thermal properties, which depend substantially on the crystallization or melting of the polymer, are Hsted in Table 1. See also reference 13. 

Table 13.11 Orthorhombic unit cells proposed for indexation of H-MoN (a) and L-MoN (b)... 

Subjecting these vectors to the crystallographic symmetry operations generates the four possible representations of the base vectors shown in table 1. The x, y, z directions in table 1 are taken parallel to the a, b, c axes of the orthorhombic unit cell in space group Pbnm. 

In order to calculate the lattice parameter for a noncubic substance, a system of linear equations with the help of the relations reported in Table 4.3 is formed, and then this system is solved. It is easier to understand the procedure with an example hence, we use the BaCe0 95Yb0 05O3 5 perovskite that crystallizes in an orthorhombic unit cell [34] to illustrate the methodology [32],... 

As shown in Table 5, the structure of Cr3S4 is built up of four anion layers. The body-centred orthorhombic unit cell (160) (a = ao, V = j/ 3 ao, c = 2 co) undergoes a slight monoclinic distortion caused by small displacements of the anions. Half the anions have five cation neighbours whereas the other half have only four. The displacements are such that each anion obtains the same charge (160). In Cr3S4 = Cr2+Cr +S4... 

Table 19 Crystal and molecular structure parameters of fibrous sulfur, [8, 54, 128-130]. The pseudo-orthorhombic unit cell proposed by Tuinstra has been overcome in favor of a monoclinic structure. The unit cell contains eight segments of ten atoms of the helices ...

Figure 1.52 shows the Bravais unit cells of the orthorhombic (Pmmm = D ) and tetragonal (P4lmmm = forms. The former is a distorted, oxygen-deficient form of perovskite. The orthorhombic unit cell contains 13 atoms, and their possible site symmetries can be found from the tables of site symmetries (Appendix X) as follows ... 

Iron oxychloride FeOCl presents a layered structure encountered in the various MOX derivatives of 3d elements that have been prepared, i.e., TiOCl, VOCl, CrOCl, FeOCl, TiOBr, VOBr, CrOBr. Table 1 shows the parameters of the orthorhombic unit cell. 

Calculation of the parameters of the crystalline phase allowed to assume the existence of an orthorhombic unit cell for a copolymer of 1,8-ANSA +An 1), which is confirmed with the data on the structure of the crystalline phase of polyaniline doped with heteropolyacids [7 7], obtained by means a modified structural model [75], Calculation of the structure of the copolymer 1.8- 7VS4 with An (1 1) allowed us to determine the unit cell parameters a = 0.585 b = 1.174 c = 1.398 nm. The resulting calculated values of the scattering peaks and the interplanar distances for the most intense reflections showed good agreement with experimental data (Table 1). 

The best fit to the observed X-ray data yielded orthorhombic unit cells for all the intercalates (Table 1) however, the standard deviation for these fits was around 0.2 A. Cell expansion along the c-axis indicates that these planar organic species are going into the material at an angle of nearly 45°. This can be deduced from a simple geometric consideration of the guest species. In the case of tetracene, which is 13.9 A long and 7.2 A wide, the cell... 

Table 1. Real and Reciprocal Space Relationship in an Orthorhombic Unit Cell...

The results of such calculations for semi-crystalline polyethylene have been reviewed elsewhere [37]. A rather wide range of predicted values is obtained, due to the choice of force constants and also to sensitivity to detailed assumptions on the unit cell structure. In spite of these limitations the principal predictions for the elastic anisotropy are clear. These include the anticipated high values for C33 and the very low values for the shear stiffnesses C44, C55 and cee, which reflect the major differences between bond stretching and bond bending forces that control C33 and the intermolecular dispersion forces that determine the shear stiffnesses. It is therefore of value to compare such theoretical results with those obtained experimentally. Table 7.3 shows results for polyethylene where data for the orthorhombic unit cell at 300 K are used to calculate these constants for an equivalent fibre (Voigt averaging procedure see Section 7.5.2 below) compared with ultrasonic data for a solid sheet made by hot compaction. It can be seen that... 

The Sc-Co phase diagram, which is shown in fig. 7 is based primarily on the results reported by Markiv et al. (1978). The authors confirmed the occurrence of the compounds ScCo2, ScCo, SciCo (table 5) and discovered a new one, SC3C0 with an orthorhombic unit cell. Chabot and Parthe (1978) established its crystal structure (table 5). There were controversial data about the crystal structure of the SC2C0 compound. Gladyshevsky et al. (1964) reported it to be of Ti2Ni type, however, these data were not confirmed by Aldred... 

The halogens chlorine, bromine, and iodine crystallize in the same space group Bmab. [This is identical to Cmca (No. 64) in The International Tables for X-ray Crystallography, vol. I, except for an interchange of the b- and c-axes.] The orthorhombic unit cell contains eight atoms in special position 8(f). 

Finally, within some of the systems are subsystems that have additional atoms or ions or molecules. These subsystems differ only by having corner species in other parts of the unit cell, like the sides or the center of the unit cell. Table 21.2 lists these details, and Figure 21.9 shows examples of the additional possible cubic, tetragonal, orthorhombic, and monoclinic crystal structures. These 14 possible crystal structures are called the Bravais lattices, after the French scientist Auguste Bravais (1811-1863), who first described them in 1848. 

The three pertinent crystal classes are differentiated in Table 6-3 by their unit cell lattice constants. Rutile and priderite have tetragonal unit cells, while pseudobroo-kite has an orthorhombic unit cell. They are more thoroughly characterized in the PDF database ll... 

PHB crystallizes with an orthorhombic unit cell, P2 P2 P2 with a = 5.76 Kb - 13.20 A, c = 5.96 A [34-37]. Two chains, each with 2 left-handed screw symmetry pass through the unit cell, with the chains packed in an antiparallel fashion. The PHV unit cell is very similar and has a = 9,32 A, b = 10.02 A and c = 5.56 A [40, 41]. As one moves across the HV range from the homopolymer up to the 40% HV copolymer there is an increase in the a spacing as the PHB lattice expands to incorporate the bulkier HV units. An expansion in the b parameter has also been observed but the c spacing (the fibre repeat) remains constant. Increasing the HB content in the HV lattice leads to a slight decrease in b as the lattice contracts (Table 5.5) [35].. ... 

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