On the basis of high-resolution x-ray diffraction measurements, the strain-stress analysis of GaN/(00.1)α-Al2O3 heteroepitaxial structures grown by molecular beam epitaxy is performed. The deformation state of the heteroepitaxial structures is investigated depending on the relative content of N in the Ga1-xNx buffer layer with the given thickness (=4 nm) and growth conditions. Using the extrapolating technique, the a- and c-lattice parameters, as well as the in-plane and out-of-plane strains (of the order of -10-3 and 10-4, respectively) are determined for GaN epilayers from θ-2θ x-ray diffraction spectra. For GaN epilayers, both the biaxial in-plane and in-depth strains (of the order of -10-3 and 10-3, respectively) and the hydrostatic strain component (of the order of -10-4) are extracted from the measured strains. It is supposed that the hydrostatic strain in the epilayers is caused by native point defects. The maximal level for the biaxial stress in the GaN epilayer, -1.3 GPa, is achieved for the sample with a relative content, x = 0.377, of N in the Ga1-xNx buffer layer.

Research on cement hydration was performed at the full-field soft transmission X-ray microscope XM-1 located at beamline 6.1.2 at the Advanced Light Source (ALS) in Berkeley CA which is operated by the Center for X-ray Optics, Lawrence Berkeley National Laboratory, Berkeley, California. A series of works [1][2][3] has been conducted using this microscope for the insitu observation and qualitative analysis of through-solution hydration products and products of topochemical reactions, which form in cementitious aqueous solutions. This paper studies the precipitation of the calcium hydroxide (CH) crystals from the cement solution. The analysis of successive images of the hydration process provides critical quantitative information about the growth rate of calcium hydroxide (CH) crystals, the supersaturation ratio, and the kinetic and diffusion coefficients of the growth process.ASTM Type II portland cement and 6% 4 3 C A S admixture were mixed in aqueous solution and saturated with respect to CH and gypsum. The 4 3 C A S admixture was included in the experimental program because of the general research program on expansive cements, and adding 4 3 C A S to portland cement is an efficient method of generating ettringite and significant early-age expansion. The solution/solid materials ratio was 10 cm 3 /g, which is higher than the one existing in regular concrete and mortars; to compensate for this dilution, the solution was originally saturated with CH and gypsum. To allow sufficient transmission of the soft X-rays, a small droplet was taken from the supernatant solution and assembled in the sample holder, and then squeezed between two silicon nitride windows for the analysis. The X-ray optical setup of the microscope XM-1 is described elsewhere [2].In this experiment, a wavelength of 2.4 nm (516.6 eV) was used. The radiation transmitting the sample was detected using an X-ray CCD camera, with a resolution of 35 nm provided by

This work presents theoretical and experimental X‐ray diffractometry investigations of the morphology and deformation state of calcium hydroxide (Ca(OH)2, CH) crystallites in the interfacial transition zone of concrete. Based on the developed theoretical approach, the distributions of CH crystallites and their coherent domains over strains and sizes are reconstructed. The average amounts of planar defects, cracks, and possible stacking faults within a CH crystallite are estimated. A comparative analysis is conducted for the morphology of CH texture depending on the type of aggregate particles (granite and smoky quartz) used.

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Ambartsumian's invariance principle is generalized for the case of coherent scattering of plane monochromatic waves by the material with arbitrary distribution of scattering charges. Particularly, X‐ray diffraction on distorted crystals is investigated. The problem of X‐ray diffraction on superlattice or a laminar crystalline medium (LCM) is solved in conditions of an extremely asymmetric geometry of reflection. It is shown, that in the conditions of diffraction the specular reflected wave “feels” the crystal distortion, not connected with the change of the mean density. This effect has resonance character. The received analytical expressions also describe the complanary three‐waves diffraction on LCM.