X-ray Diffraction Profiles (x-ray + diffraction_profile)

Distribution by Scientific Domains

Selected Abstracts

Redetermination of the crystal structure of ,-copper phthalocyanine grown on KCl

Akitaka Hoshino
The crystal structure of a polymorph of copper phthalocyanine (CuPc) grown on a KCl substrate is redetermined by transmission electron diffraction. It has a triclinic unit cell containing one molecule; the crystal does not have a herringbone-type molecular arrangement, which is a common packing mode of planar phthalocyanines. The molecular packing is determined by the diffraction intensity with the aid of the calculation of molecular packing energy. One of the striking features of this polymorph is its stacking mode within a molecular column: the molecular stacking direction projected on a molecular plane is different by an angle of about 45° from that of the ,-modifications of platinum phthalocyanine (PtPc) and metal-free phthalocyanine (H2Pc). A powder X-ray diffraction profile calculated for the polymorph agrees well with that of so-called ,-CuPc and Rietveld analysis for ,-CuPc indicates that the CuPc crystals grown on KCl are actually ,-CuPc; hence, ,-CuPc is not isostructural with either ,-PtPc or ,-H2Pc. On the basis of the present results and the reported crystal structures of the planar phthalocyanines that form molecular columns, the polymorphs of the phthalocyanines can be classified into four types distinguished by the molecular stacking mode within the column: ,(×)-, ,(+)-, ,(×)- and ,(+)-types. [source]

Quantitative microstructural and texture characterization by X-ray diffraction of polycrystalline ferroelectric thin films

Jesús Ricote
Texture becomes an important issue in ferroelectric materials as it greatly influences the physical properties of polycrystalline films. The use of advanced methods of analysis of the X-ray diffraction profiles, namely quantitative texture analysis or the recently developed combined approach, allows access to quantitative information on the different components of the global texture and to more accurate values of structural and microstructural parameters of both the ferroelectric film and the substrate, not available by more conventional methods of analysis. The results obtained allow important conclusions to be drawn regarding the mechanisms that lead to the development of preferred orientations in thin films and, also, the correlation between them and the ferroelectric behaviour. For example, it is observed that the inducement of a strong ,111, texture component does not mean the complete disappearance of the so-called `natural' ,100,, ,001, components, and that the ratio between the contributions to the global texture of these two components can be changed by the presence of tensile or compressive stress during crystallization of the films. The relative contributions of these texture components are also related to the final properties of the ferroelectric films. [source]

A general approach for determining the diffraction contrast factor of straight-line dislocations

Jorge Martinez-Garcia
Dislocations alter perfect crystalline order and produce anisotropic broadening of the X-ray diffraction profiles, which is described by the dislocation contrast factor. Owing to the lack of suitable mathematical tools to deal with dislocations in crystals of any symmetry, contrast factors are so far only known for a few slip systems in high-symmetry phases and little detail is given in the literature on the calculation procedure. In the present paper a general approach is presented for the calculation of contrast factors for any dislocation configuration and any lattice symmetry. The new procedure is illustrated with practical examples of hexagonal metals and some low-symmetry mineral phases. [source]

Determination of lattice parameters and thermal expansion of CuGe2P3 + 0.2 Ge3P4 at elevated temperatures

G. Bhikshamaiah
Abstract CuGe2P3 is a p-type semiconductor with zincblende structure. Ge3P4 is soluble up to 35 mole% in CuGe2P3. Lattice parameters of CuGe2P3 + 0.2 Ge3P4 have been determined at elevated temperatures from room temperature to 873 K using the x-ray diffraction profiles (111), (200), (220), (311), (222), (400), (331), (420), (422) and (511) obtained from high temperature diffractometer. It is found that the lattice parameter increases linearly from 0.53856 nm at RT to 0.54025 nm at 873 K. The data on lattice parameter is used and coefficient of lattice thermal expansion of CuGe2P3 +0.2 Ge3P4 was determined at different temperatures. It is found that the coefficient of thermal expansion of CuGe2P3 +0.2 Ge3P4 is 5.48 x 10 -6 K -1 and is independent of temperature. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]