Inhomogeneities In Single Crystals Research Articles

Microstructure of single crystals of austenitic stainless steel

Auger spectroscopy and x-ray structure analysis have been used to study the chemical and phase inhomogeneity in single crystals of the austenitic nitrided stainless steel Cr22Ni17Mo3 with various morphologies of the dendritic structure. In single crystals grown in the 〈100〉 direction with a classical dendritic structure the interaxial regions are highly enriched with S, N, and C and weakly enriched with Mo, V, and Mn. At the same time these regions have a high density of particles of the type Me23C6, Me7C3, and vanadium carbonitrides, oriented in the growth direction. The axial regions have a subcellular structure, with oxygen-rich subcell boundaries. In single crystals with growth direction close to 〈110〉, in which only secondary dendrite axes are formed, the alloying elements, impurities, and second-phase particles are distributed relatively uniformly throughout the ingot.

IN SITU INVESTIGATION OF NUCLEATION, GROWTH, AND DISSOLUTION OF SILICATE CRYSTALS AT HIGH TEMPERATURES

Imperfections and inhomogeneities in single crystals of minerals and the textures of rocks and ores appear primarily as a result of nucleation and growth of crystals, and secondarily through post-growth histories such as dissolution, exsolution, and phase transition. How and under what conditions mineral crystals nucleated, grew, dissolved, or transformed, how rock textures appeared, and what sort of post-growth histories they experienced have been deduced by analyzing these characteristics. Inves­ tigations of earth and planetary materials along this line are as important as equilibrium thermodynamic analyses of mineral parageneses, since they provide information on kinetic processes. Various sophisticated methods have been used to detect and analyze these characteristics, including optical and electron microscopies, electron probe micro-analysis and other surface analysis methods, cathode luminescence topography, X-ray topography, laser-beam tomography, etc. A deductive analysis of this type, however, should be supplemented by a theoretical and experimental understanding

Visualization of internal domain structure of silicon iron crystals by using neutron radiography with refraction contrast

It is shown that visualization of individual domain walls and domain structure inhomogeneities in single crystals of ferromagnets is possible by using the method of neutron radiography with refraction contrast. Images of the internal domain structure of bulk (≈ 1 cm) silicon iron single crystals of different orientations are obtained.

Some Mössbauer effect considerations in gamma-ray laser development

The development of gamma-ray lasers (grasers) will, in all probability, depend on the use of recoillessly emitted gamma rays from nuclear transitions, i.e., the Mössbauer Effect (ME). Past research in Mössbauer spectroscopy which relates to grasers is briefly reviewed. The nuclear lifetimes, required for practical considerations, may have to be on the order of seconds, if storage and transfer processes prove infeasible. It is not clear that the ME has been observed in such long-lived states. Even if such long-lived states are not needed directly for grasers, successful observation of the ME in such a system will answer important questions of line broadening due to field inhomogeneities in single crystals. We propose some novel experimental schemes to observe the ME in 109Ag whose relevant lifetime is about 40 sec. The techniques proposed are: coincidence Mössbauer spectroscopy, conversion-electron Mössbauer spectroscopy, gravitational line sweeping, and gamma-ray self-absorption. Preliminary results using the later technique are presented. Possible future, relevant ME research is discussed.

Inhomogeneities in potassium single crystals revealed using the de Haas-van Alphen effect

The variation of DHVA amplitude with measurement frequency reveals the existence of inhomogeneities in single crystals of potassium. Such inhomogeneities may be associated with dislocated or locally strained regions of the crystal and account for the orientational dependence of DHVA amplitude in this metal.

Compositional inhomogeneity of (Ba, Pb)TiO 3 crystals

Optical microscope studies of ferroelectric transition behavior have been correlated with direct analysis by the electron microprobe for characterization of patterns of inhomogeneity in single crystals of (Ba, Pb)TiO 3 from two different flux systems. Seed-grown crystals from a borate flux showed both a gradual zoning effect, and a fluctuation of the Pb/Ba distribution associated with growth striations and a related domain structure. The systematic changes in Pb content of butterfly-twin crystals from KF solution were useful in tracing the detailed history of the growth process.