The annealing of solution-crystallized polyethylene mats: an X-ray diffraction study

Both low- and wide-angle X-ray diffraction measurements have been made on solution-crystallized mats of high density polyethylene which have been annealed for different periods at 125° C. The low-angle data, in addition to showing the rapid increase in both long period and density defect at each fold surface for the first stages of annealing, also indicate that after annealing for times in excess of 10⁵ sec the density defect is reduced and approaches the value for the unannealed crystal. The wide-angle X-ray studies have centred around the Fourier analysis of the 0 0 2 diffraction peak. The results of this type of measurement on unannealed mats have already been reported [20]. In extending the work to annealed material evidence has been obtained for preferred chain stem lengths which are multiples of the unannealed length. The combination of these observations with the low-angle results has led to the formulation of a model for crystal thickening which invokes the unlooping mechanism proposed by Dreyfuss and Keller [15], but also envisages thickening occurring preferentially from one fold surface to give an asymmetric crystal profile in the [0 0 1] direction.     

Single-crystal X-ray diffraction analysis of nonplanar autoepitaxial silicon layers

We describe a method to study the structure of semiconductor autoepitaxial layers grown in the form of closed cylinders on the external side surface of hollow cylindrical single-crystal substrates. We compare the values of dislocation density in the structure of nonplanar layers obtained by single-crystal X-ray diffraction analysis (measurements of rocking curves) and by the etch pit method in the [111] plane. The results of singlecrystal X-ray diffraction analysis of nonplanar autoepitaxial silicon layers are shown to be reliable.     

Defect-induced microstructures: an X-ray diffraction analysis

Single crystal X-ray diffraction was applied in order to investigate defect-induced microstructures in radiation damaged zircon. The formation of domains with different degrees of order was observed and in particular, it was possible to distinguish two types of defects: isolated lattice defects and dislocations. These lattice deformations have a great influence on the structural and physical properties of the materials.     

Plasma-etched organic layers for antireflection purposes

Organic layers can be used to realize special functions in optical interference coatings. Suitable compounds for such layers were thermally evaporated and characterized. A plasma etching procedure was applied to produce nanostructures on top of the organic layers to reduce their effective refractive indices. Broadband antireflective coatings were obtained by combining these artificial low-index layers with conventionally prepared interference stacks.     

High-resolution X-ray diffraction and fast routine evaluation of graded hetero-epitaxial layers

The design of modern high-speed electronic and optoelectronic devices is nearly exclusively based on hetero-epitaxial layer structures, an essential part of which are composition-graded layers. For many years high-resolution X-ray diffraction has proved to be a useful method for characterizing corresponding structures. The high dynamic range and the resolution of state-of-the art diffraction systems based on multi-crystal monochromators are essential for the detailed analysis of these complex layer structures. Simulations using dynamic scattering theory have to be applied for the interpretation of the data. Due to the many adjustable parameters frequently involved this is often a time-consuming process. Recent advances in automatic fitting software offer rapid convergence even for many adjustable parameters. This allows fast and reliable extraction of layer thickness, composition and grading profile. The experimental aspects and the evaluation process of the structural characterization are discussed for different examples of hetero-epitaxial layer structures.     

X-ray diffraction study of detonation nanodiamonds

The paper addresses a structural analysis of detonation nanodiamonds. An analysis procedure is described which has been elaborated on the basis of a comparison between experimental and theoretical diffraction patterns calculated using computer models of nanodiamonds. Detonation nanodiamonds are characterized in terms of their shape, size, crystal lattice parameters, and distribution of atoms in them. The lattice parameters have been determined for new detonation nanodiamonds synthesized by us and other researchers. The quality of detonation nanodiamonds is assessed by the atom distribution which differs from that of natural diamonds and depends on the lattice parameters and size of the detonation nan-odiamonds. The lattice parameters of the detonation nanodiamonds synthesized in the presence of reductants have been found to correspond to that of natural diamond, thus suggesting a high quality of the synthetic nanodiamonds.     

X-ray diffraction study of magnesiothermic tantalum powders

We have studied the effect of specific surface area and reaction product leaching conditions on the crystal structure of mesoporous tantalum powders prepared by reducing tantalum oxide compounds with magnesium vapor.     

X-ray diffraction study of alkali titanate glasses

A Fourier analysis of X-ray diffraction spectra of vitreous 2TiO₂.K₂O and 2TiO₂.Cs₂O is presented. The Ti⁴⁺ ion is shown to be octahedrally co-ordinated with respect to oxygen, the interionic Ti-O distance being equal to 1.95 Å. The K⁺ and Cs⁺ ions are not distributed at random but are placed in contact with the three oxygens of the faces of TiO₆ octahedra constituting the network. This proves conclusively that a glass network former is capable of a regular octahedral co-ordination and shows the further need to revise the classic Zachariasen-Warren theory.     

An X-ray diffraction study of bismuthate glasses

Now at Government Industrial Research Institute, Osaka, Japan.     

X-ray diffraction study of an amorphous Al60Ge30Ni10 alloy

The ordinary X-ray diffraction profile and anomalous X-ray scattering profiles at nickel and germanium K absorption edges of amorphous Al₆₀Ge₃₀Ni₁₀ alloy have been determined. The results indicate the characteristic feature of the coexistence of nickel-rich highly ordered crystal-like regions and germanium-rich amorphous regions. From the environmental radial distribution function around germanium atoms, the coordination number around a germanium atom is estimated at about 4. Thus, an amorphous germanium-like structure may be quite feasible in this region.     

X-ray diffraction methods for the evaluation of residual stresses in the surface layers with gradient structure

We propose an X-ray diffraction method aimed at measuring residual stresses in the surface layers characterized by variable chemical compositions over the depth of the layer. The method is based on measuring the interplane distances for different diffraction reflexes with separation of the contributions of elastic stresses and the composition of a solid solution to these distances on the basis of specific features of the elastic anisotropy of the crystal lattices of metals with cubic and hexagonal structures. The efficiency of the proposed procedure is demonstrated by analyzing, as an example, éI961 and 12Kh18N10T steels, PT7M titanium alloy after ionic nitriding, and éP975ID nickel superalloy treated by electroerosion cutting. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 3, pp. 77–84, May–June, 2006.     

X-ray diffraction study of polyphilic smectic liquid crystals

4-substituted n-5,5,6,6,7,7,8,8,9,9,10,10,10-tridecafluorodecan-1-yloxybenzene and n-5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,12-pentadecafluorododecan-1-yloxybenzene, the former with CO₂CH₃ and the latter with CO₂CH₃ and CO₂H substituents in para position, are polyphilic compounds exhibiting smectic liquid crystalline phases. The structure of these phases was studied by X-ray diffraction and modelling. The method consisted of reconstructing all possible one-dimensional electron density profiles from diffraction intensities and matching them with the profiles calculated from structural models. The method is shown to be useful in both determining molecular arrangement in the smectic phase and in phase identification itself. An S_Ad phase is found in the two esters, having interdigitated perfluorinated alkyl segments. In contrast, a double-layer S_C phase, also known as S_C2, is found in the carboxylic acid. The method used here is particularly applicable to polyphilic liquid crystals such as the present ones, which are characterized by a complex electron density profile and a high translational order parameter.     

Chemical vapour deposition of silicon carbide: An X-ray diffraction study

Low-pressure chemical vapour deposition of siliconcarbide from tetramethyl silane pyrolysis was studied by X-ray diffractometry.In situ measurements at high temperature gave kinetic information. The crystallization state, grain size, microstrains and residual macrostresses were measured at room temperature.     

Synthesis and X-ray diffraction study of radium plumbate

Previously unknown mixed oxide RaPbO₃ was prepared by thermal decomposition of a mixture of radium and lead carbonates. An X-ray diffraction study showed that radium plumbate crystallizes in the cubic perovskite structural type. The unit cell parameter (a = 4.303 Å) and crystallographic density (ρ = 10.42 g cm^?3) were determined. Formation of a new compound, RaPtO_3?x , upon sintering of mixtures of radium and lead carbonates at 800°C in a platinum crucible was detected. A similar barium compound can be formed upon calcination of barium compounds in platinum vessels in air.     

X-ray diffraction study of Ge-Bi-Te mixed-layer ternary compounds

The structures of the Ge₃Bi₂Te₆, GeBi₆Te₁₀, and Ge₂Bi₁₀Te₁₇ compounds, belonging to thenGeTe ·mBi₂Te₃ homologous series, were studied by x-ray diffraction. For Ge₃Bi₂Te₆, the atomic coordinates, lattice parameters, and interatomic distances were determined. This compound was shown to contain mixed (Ge + Bi) cation layers. The c parameters of the hexagonal cells of GeBi₆Te₁₀ and Ge₂Bi₁₀Te₁₇ were determined. It is shown that the x-ray patterns from the cleaved surfaces of single-crystalnGeTe ·mBi₂Te₃ compounds vary in a systematic manner with increasingn/m ratio, which is attributable to the filling of empty Te octahedra. For 00l reflections, indexl can be expressed in general form throughn andm.     

冷轧变形纳米晶钴的X射线衍射研究

对冷轧变形前后纳米金属钴的微观应变。晶格常数以及晶粒尺寸的变化进行了研究，对X射线衍射图谱进行了分析计算，结果表明，变形过后晶体内部存有残余内应力并导致了微观应变，应变大小为ε=1．412×10q；对变形前后的晶格常数进行计算，得到变形后的晶格常数为a=0．25241nm；c=0．40782nm；透射电镜的观察和衍射谱线的计算表明变形后纳米金属钴的晶粒大小与形状基本未发生变化，平均晶粒尺寸为18．8nm。有可能是空位的活动降低了变形过程中的晶界迁移几率，使得变形后的晶粒尺寸基本没有发生变化。     

X-ray diffraction study of Cu1.8Zn0.2Se

Partial substitution of Zn at the Cu site in Cu₂Se stabilizes the high-temperature, fcc phase to room temperature. The temperature stability limit of the low-temperature, orthorhombic phase shifts to 873 K.