Analysis Of Structural Distortions Research Articles

Analysis of structural distortion in Eshelby twisted InP nanowires by scanning precession electron diffraction

Transmission electron microscopes (TEM) are widely used in nanotechnology research. However, it is still challenging to characterize nanoscale objects; their small size coupled with dynamical diffraction makes interpreting real- or reciprocal-space data difficult. Scanning precession electron diffraction ((S)PED) represents an invaluable contribution, reducing the dynamical contributions to the diffraction pattern at high spatial resolution. Here a detailed analysis of wurtzite InP nanowires (30–40 nm in diameter) containing a screw dislocation and an associated wire lattice torsion is presented. It has been possible to characterize the dislocation with great detail (Burgers and line vector, handedness). Through careful measurement of the strain field and comparison with dynamical electron diffraction simulations, this was found to be compatible with a Burgers vector modulus equal to one hexagonal lattice cell parameter despite the observed crystal rotation rate being larger (ca. 20%) than that predicted by classical elastic theory for the nominal wire diameter. These findings corroborate the importance of the (S)PED technique for characterizing nanoscale materials.

A Novel Image Quality Assessment Metric based on Image Gradient Vectors

Image degradation deforms the structure of image, thus analysis of structural distortions of image is beneficial to image quality assessment (IQA). This paper proposes a novel structural information-based IQA metric, in which image gradient vector, composed of magnitude and phase components, is used to describe the structural information of an image. Since the phase quantization code of the phase component can also reflect the change of image quality to some extent, Hamming distance between the phase quantization code of the reference and distorted images is defined to represent the quality map of an image for quality assessment. Because different regions in image are with different importance for human visual perception, threecomponent image model for IQA is exploited according to the gradient magnitude component, and nonuniform weights are designed to emphasize the importance of different regions in image. Experimental results of the LIVE database show that the proposed IQA metric is more consistent with subjective results, and has higher correlation coefficients compared with other classic IQA metrics.

Crystal chemistry of the MgAl2O4-MgMn2O4-MnMn2O4 system: Analysis of structural distortion in spinel- and hausmannite-type structures

Single crystals of spinel and hausmannite having seven different compositions in the MgAl2O4-MgMn2O4-MnMn2O4 system were synthesized and structurally and chemically characterized by X-ray diffraction and electron microprobe techniques. As predicted, tetrahedral and octahedral bond lengths increase with increasing substitutions of Mn2+ for Mg and Mn3+ for Al, respectively. A transition from cubic to tetragonal symmetry occurs at a critical concentration of Mn3+ > 1.4 atoms per formula unit as a result of the Jahn-Teller distortion around octahedrally coordinated Mn3+. The present data in conjunction with data from the literature provide a basis for quantitative analyses of the cation polyhedral-distortion parameters and their variations in spinel- and hausmannite-type structures ( Fd 3 m and I 41/ amd , respectively). In contrast to the linear correlation between (octahedral quadratic elongation) and σ2M (octahedral bond-angle variance) observed for many silicates and isomorphic structures, these two distortion parameters are not correlated in multiple oxides with spinel- and hausmannite-type structures. By using a model of multiple linear regression, it is demonstrated that varies as a function of both σ2M and ΔM (octahedral bond-length distortion). The degree of octahedral distortion is significant in the spinel structures and is in fact comparable with that calculated for the hausmannite-type structures. The degree of octahedral distortion is related to steric effects in both spinel- and hausmannite-type structures, whereas the electronic effects caused by Mn3+ account for the transition from cubic to tetragonal symmetry.

Warp breakage mechanism of friction spun yarns

Warp breakage mechanism of Dref, ring, and rotor spun yarn is discussed using five different techniques,which include Weibull distribution, fatigue behavior, scanning electronmicroscopy studies, and analysis of structural distortion by digital image processing. In all types of yarn, failure occurs at minimum diameter. Interfibre slippage is a dominant factor for warp breakage and the slippage length is found to be highest for Dref yarns.

Cation-site partitioning in Ti-rich micas from Black Hill (Australia): A multi-technical approach

AbstractThe crystal chemistry of Ti-rich trioctahedral micas of plutonic origin, cropping out at Black Hill (South Australia) has been investigated by combining electron microprobe analysis, single crystal X-ray diffraction, Mössbauer spectroscopy and X-ray photoelectron spectroscopy. Chemical analyses have shown the samples taken to be quite homogeneous and Ti-rich (TiO2 ≈ 7 wt.%). Mössbauer investigation yielded Fe2+/Fe3+ ≈ 30. X-ray photoelectron spectroscopy analysis seems to suggest the occurrence of three Ti species: octahedral Tr4+(60%), octahedral Ti3+(26%), and tetrahedral Ti4+(14%). The analyzed sample belongs to the 1M polytype and the relevant crystal data from structure analysis are: a = 5.347(1) Å, b = 9.261(2) Å, c = 10.195(2) Å, β = 100.29°(1). Anisotropic structure refinement was performed in space group C2/m, and converged at R = 2.62, Rw = 2.80. Structural details (the c cell parameter, the off-center shift of the M2 cation towards 04, the bond-length distortions of the cis-M2 octahedron, the interlayer sheet thickness, the projection of K−O4 distance along c*, the difference <K−O>outer-<K−O>inner) support the occurrence of the Ti-oxy substitution (VIR2+ + 2(OH)− ⇌ Ti4+ + 202− + H2) in the sample. Analysis of structural distortions as a function of the Ti content revealed that the positions of the oxygens 03 and 04 are displaced in opposite senses along [100]. This produces an enlargement of the M1 site with respect to the M2 site and a shortening of the interlayer distance. This trend seems to be in common with other Ti-rich 1M micas of plutonic origin.

Analysis of structural distortions in non-stoichiometric ternary platinum oxides: Li0.64Pt3O4 and Co0.37Na0.14Pt3O4

The structures of Li0.64Pt30 4 and Co0.37Na0.14Pt30 4 have been determined from neutron powder diffraction experiments and found to exhibit two kinds of internal structural distortions distinguishing them from the prototype NaPt304 structure in which the Na counterion occupies eight-coordinated cubic sites in the PtO 4 framework. Both the Li0.64Pt30 4 and Co0.37Na0.14Pt30 4 structures were characterized by modifications to the geometry of the eight-coordinated counterion site. In Li0.64Pt30 4 the Li ions were randomly distributed on these sites, and the oxygen coordination was no longer cubic, with four short Li-O distances of 2.22/k and four long ones of 2.65 A in the configuration of two interpenetrating tetrahedra. In Co0.37Na0.14Pt304 there was ordering of Co, Na, and vacancies in the eight-coordinated sites, which imposed a structural limit on substitution of eight-coordinated atoms to 0.5 per formula unit. In this case, cationoxygen coordination was cubic, with eight O atoms at a distance of 2.36 (1)A from the occupied counterion site. The Li0.64Pt30 4 structure, with a = 5.6242 (2)A and Z = 2, was refined in space group P43n by the Rietveld profile technique with a final weighted profile discrepancy factor Rwe = 0.160 for 35 reflections collected at 2 = 1.343/1,. The Co0.37Na0.14Pt30 4 structure, with a = 5.6321 (4)/i, and Z = 2, was refined in space group Pm3 using integrated intensities with a final weighted R w = 0.036 for 15 observations representing 22 reflections collected at 2 = 2.460/~.