Lead crystal structures, lattice parameters

The crystal structure measurements were carried out using high temperature X-ray diffraction. Reference measurements were also obtained at 25°C, from which the lattice parameters, a = (3.233 0.001) x 10 m and c = (5.1475 0.0015) x 10 m, axial ratio, ate = (0.6281 0.0004), unit eell volume, (46.595 + 0.037) x 10 m and density, (6.501 0.005) g-cm were determined. High temperature measurements were taken from 950 to 1164 K for a-zirconium, however, there was a reasonable amount of scatter in the data obtained at these temperatures. Crystal structure measurements were also taken for p-zirconium. For this phase, reference measurements were taken at 1252 K leading to a lattice parameter of a = (3.6162 + 0.0020) x 10 m, a unit cell volume of (47.285 0.080) x 10 m" and a density of (6.406 0.011) g-cm ... 

The lattice constants for undoped GaN and the highly conductive Ga Zn and GaN Ca bulk crystals vary slightly for different crystals as well as for different areas of the individual crystals [26,28], This is caused by the differences in free electron concentration and can lead to certain strains in the crystals. For the Mg-doped crystals, there are no free electrons and therefore the lattice parameters are uniform for individual crystals and the same for different samples [28], Elimination of the strains in the GaN Mg crystals is the reason for the improvement of their structure. The rocking curves are narrower and no low angle boundaries are observed even for 8 mm single crystalline GaN Mg platelets. The strains in the undoped GaN crystals are extremely small (<0.02%) but their presence can adequately explain the wider rocking curves than for the Mg-doped samples. 

Ceria-zirconia nanophases were synthesied by a surfactant-assisted method. The refined structural data concerning the crystallite size, lattice parameters, structural microstrain, cationic occupy number and cationic defect concentration are reported. Zirconium addition into the cubic structure of ceria inhibits crystal sintering but leads to structure distortion. Different CO-metal bonds are formed when CO chemisorbs on Pd-loaded CesZr. x02 catalysts. Catalytic tests reveal that the lower zirconium content benefits the CO oxidation. 

A simple indexing exercise is the case of the crystal structure LaBg (NIST Reference St andard Material 660A), certified cell u = 4.1569162 A, whose observed (by a conventional diffractometer) d u values in A are given in Table 7.4. If a cubic lattice is supposed and the Miller indices (100) are tentatively assigned to the first observed line (t//j /=4.1605 A), then An, as defined in Table 7.3, leads to the direct cell parameter, by means of which all the remaining lines can be indexed. 

The X-ray powder diffraction study published by Tourne and Tourne is the main reference for the metal-substituted Keggin anionsJ" " These authors studied the K+, Rb+ and NH4+ salts and verified that they crystallized in a small number of structural types, depending on the number of cations in the molecular formula. The water molecules of crystallization also have a small role, as they reinforce the crystal cohesion and influence the orientation of the anions. Loss of water leads to loss of crystallinity and may alter the lattice parameters. 

Orthorhomh-PhO also has a layered structure the layers are huilt of infinite Pb—O chains [2] as shown in Fig. 5.1. The surfaces of the layers are composed of Ph ions and each oxygen ion is surrounded hy four lead ions. The chain layers are stabilised by van der Waals bonds [2]. Therefore, the orthorhombic-PbO crystals are prone to flaking. In the covalent pattern, the electron pairs are localised and their delocalization requires excitation. This is responsible for the very low dark electric conductivity of orthorhomb-PbO. The following are the lattice parameters of the elementary cell a = 5.489 A, b = 4.755 A and c = 5.891 A. The melting point of orthorhombic PbO is 885 °C and the boiling point is 1480 °C. 

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