Crystal chemistry of layered structures formed by linear rigid silyl-capped molecules

The crystallization behavior of methylthio- or methylsulfonyl-containing spacer extendedZ,Z-bis-ene–yne molecules capped with trimethylsilyl groups obtained by (tandem) thiophene ring fragmentation and of two non-spacer extended analogs were investigated. The rigid and linear molecules generally crystallized in layers whereby the flexibility of the layer interfaces formed by the silyl groups leads to a remarkably rich crystal chemistry. The molecules with benzene and thiophene spacers both crystallized withC2/csymmetry and can be considered as merotypes. Increasing the steric bulk of the core by introduction of ethylenedioxythiophene (EDOT) gave a structure incommensurately modulated in the [010] direction. Further increase of steric demand in the case of a dimethoxythiophene restored periodicity along [010] but resulted in a doubling of thecvector. Two different polytypes were observed, which feature geometrically different layer interfaces (non-OD, order–disorder, polytypes), one with a high stacking fault probability. Oxidation of the methylthio groups of the benzene-based molecule to methylsulfonyl groups led to three polymorphs (two temperature-dependent), which were analyzed by Hirshfeld surfacede/difingerprint plots. The analogously oxidized EDOT-based molecule crystallized as systematic twins owing to its OD polytypism. Shortening of the backbone by removal of the aryl core resulted in an enantiomorphic structure and a further shortening by removal of a methylthio-ene fragment again in a systematically twinned OD polytype.

Size and Strain Analysis of Deformation Microstructure in High-Nitrogen Austenitic Stainless Steels

Deformation microstructure of Fe-18Cr-10Mn alloys with different nitrogen content (0.39 and 0.69N) were investigated using neutron diffraction. The deformation mode changed from strain-induced martensitic transformation (SIMT) to deformation twinning (DT), as nitrogen content was increased. The measured neutron profiles of tensile-strained bulk samples were fitted by modified Thomson-Cox-Hasting profile-shape function and the Lorentzian and Gaussian integral breadths were calculated based on Rietveld refinement. With the calculated integral breadths, the mean-squared (MS) strain could be evaluated using the size and strain analysis of double-Voigt approach. Based on the analysis of peak shift of individual reflections, the stacking fault probability (SFP) was determined. Although the calculated SFP and MS strain varied with the degree of deformation, the ratio of MS strain to SFP remained constant for each alloys regardless of tensile strain, but increased with nitrogen content. As a result, it was found that the SFE increased with increasing nitrogen content. The nitrogen-induced transition of deformation microstructure was accounted for by the change in SFE, as reported in other fcc materials.

Plastic Deformation and the Role of Fault Formation in the Equation of State of Micron Size Intermetallic Alloys Under Non-Hydrostatic Pressure

ABSTRACTThe elastic and plastic deformation of micron size anisotropic polycrystals of Ni3Al and Cu3Au intermetallic alloys have been studied under non-hydrostatic conditions by energy-dispersive X-ray diffraction (EDX) in a diamond-anvil cell. Compression was achieved by confining the samples in a viscous fluid or directly between the diamond anvils. Deviatoric forces are introduced in the samples as a result of the increasing viscosity with pressure and the eventual glassification of the pressurizing medium or by the contact forces of the diamond anvils. Line shifts and line profiles were used to analyze elastic and plastic strains. Plastic deformation is due to the onset of non-hydrostatic stresses and the introduction of stacking faults and dislocations. A volume incompressibility due to plastic deformation and the saturation of the stacking fault probability is followed by an elastic compression of a fully plastically deformed state. The compression of this state is isotropic and independent of the presence and type of the pressurizing medium. From the measured strains at different crystallographic orientations, the uniaxial stress and the stacking fault probability as a function of the confining pressure are derived and their role in the equation of state is examined. Using finite elasticity, the equation of state is derived in the presence of uniaxial stresses causing stacking faults, defects and dislocations.