Metastable cubic Ge2Sb2+x Te5 compounds, which can be prepared only as thin films, have been studied by both of neutron and x-ray powder diffraction measurements. Large displacement of germanium atoms in a crystalline cubic Ge2Sb2Te5 phase is found by PDF analysis. By adding Sb, the crystalline cubic phases coexist with two types of amorphous phases, depending on the quenching temperature. One has a first sharp diffraction peak similar to the amorphous Sb at Q ∼1.1 Å−1. Another has a new peak at Q ∼0.74 Å−1. Based on our crystal structure analyses, the composition of the new amorphous phase was estimated to be about Ge7Sb8Te10. The composition of the crystalline solid was also found to be different from the matrix, resulting in the nucleation dominated crystal growth in this system.

In the past years the concept of measuring strain by x-rays has changed significantly. The combination of 3rd generation synchrotron sources, advanced focusing techniques and large area detectors has made it possible to probe volumes smaller than a cubic micron. This devolopment has made it possible to probe microstrains directly without having to rely on highly sophisticated models to evaluate peak broadening effects. This paper will provide a review of the state of art of local strain measurements by x-rays, discuss their limitations, provide an outlook of where the field may be going within the next years and address the most important issues to be solved. Examples will be given for the current limits in terms of resolution in time, space, strain and intensity.

Interpenetrating Al2O3/Al composites were created by liquid-metal infiltration of alumina preforms with three-dimensional periodicity produced by a robotic deposition method. Volume-averaged lattice strains in the alumina phase were measured by synchrotron x-ray diffraction at various uniaxial compression stresses up to 350 MPa. Load transfer, which is experimentally found to occur between the aluminum and the alumina phase, is in agreement with simple rule of mixtures models. Spatially resolved measurements showed variations in load transfer at different positions within the composite for the elastic-, plastic-, and damage-deformation regimes. Using phase-enhanced imaging, the extent of damage within the composites was observed.

The deformation behavior of BCC metals is being investigated by x-ray microdiffraction measurements (μXRD) for the purpose of characterizing the dislocation structure that results from uniaxial compression experiments. The high brilliance synchrotron source at the Advanced Light Source (Lawrence Berkeley National Lab) and the micron resolution of the focusing optics allow for the mapping of Laue diffraction patterns across a sample. These measurements are then analyzed in order to map the distribution of residual stresses in the crystal. An important finding is the observation of Laue spot “streaking”, which indicates localized rotations in the lattice. These may represent an accumulation of same-sign dislocations. Theoretical modeling of the diffraction response for various slip systems is presented, and compared to experimental data. Preliminary results include orientation maps from a highly strained Ta bicrystal and a less highly strained Mo single crystal. The orientation maps of the bicrystal indicate a cell-like structure of dense dislocation walls. This deformation structure is consistent with previous OIM studies of the same crystal. The results suggest that μXRD may be a particularly useful tool for microscale studies of deformation patterns in a multi-scale investigation of the mechanisms of deformation that ranges from macroscopic deformation tests to high resolution TEM studies of dislocation structures.

The shear orientation of three polymer-clay gels has been investigated by means of small angle neutron scattering (SANS). The gels have the same polymer and clay concentrations but different polymer molecular weight. The polymer is adsorbed to the clay platelets. While long polymer chains can interconnect several platelets shorter polymer chains cannot. Although the polymer concentration is above c* the polymer chain length and cross linking between clay platelets strongly influence their shear orientation which leads to anisotropy in SANS. Our data suggest that the flow is strong enough to enhance and maintain a continuous increase in the shear orientation of the polymer clay gels only when the polymer chains are long enough to interconnect or strongly entangle between platelets.

X-ray diffraction with hard X-rays (E = 70 keV) was used to investigate the grain nucleation and grain growth during solidification of a grain refined Al-0.3Ti-0.02B (wt.%) alloy. The investigations showed for the first time the nucleation profile during solidification and how nucleation rate increases with cooling rate. The results indicate that the nucleation process is complete for solid fraction below 30 %, irrespective of the cooling rate. This is explained in terms of the release of latent heat during solidification. The growth of individual aluminium grains during solidification is experimentally observed and compared to model predictions for the diffusion limited grain growth. The experimental results are only in agreement with the theory in the first stage of the transformation. The difference between the experiment and the theory is discussed qualitatively.

Ultra-thin CoPt3 nanoparticle films have been prepared on SiO2 surfaces using a Langmuir-Blodgett (LB) deposition technique. The structural properties of the overlayers have been investigated by grazing-incidence small-angle x-ray scattering (GISAXS) and high-resolution scanning electron microscopy (SEM) for the first time. Self-assembly of the nanoparticles is found and with GISAXS an average particle-particle distance of (8.23 ± 0.06) nm is determined, in good agreement with the SEM results. A particle correlation length of (22.3 ± 1.2) nm was derived which is shown to be independent of the surface coverage. The latter quantity may be controlled by choice of a suitable retraction speed during the LB step.

The phase-diagram of Ca2-xSrxRuO4 has been studied by several diffraction techniques as function of concentration, temperature, pressure and magnetic field. The substitution of Sr through the smaller Ca induces a series of structural phase transitions with a strong impact on the physical properties. The spin triplet superconductor Sr2RuO4 exhibits an undistorted crystal structure, and the Mott-insulator Ca2RuO4 strong structural distortions. For intermediate structural distortions samples stay metallic but with outstanding properties. Throughout the phase diagram we find a close coupling between the crystal structure on one side and magnetic and electronic behavior on the other side.

Neutron reflectivity is a well-established technique for studying self-diffusion in chemically homogeneous system as neutron scattering lengths are different for isotopes of an element. For x-ray there is no contrast for a multilayer with isotopic abundance. However, placing Mössbauer active nuclei in a chemically homogeneous system, self-diffusion of the constituents can be probed using nuclear resonance scattering of Mössbauer active nuclei. In the present work, we have applied the neutron reflectivity technique for studying the self-diffusion of iron and nitrogen in nano crystalline multilayers of FeN/57FeN and FeN/Fe15N and nuclear resonance reflectivity techniques for studying iron self diffusion in FeNZr/57FeNZr. Both the techniques are complementary to each other and give a unique depth resolution of the order of 0.1 nm. As compared with conventional techniques used for probing self-diffusion, neutron and nuclear resonance reflectivity techniques can be applied at significantly lower temperatures. On the basis of the obtained results the diffusion mechanism in chemically homogeneous multilayers is discussed in the present work.

In situ specular x-ray reflectivity was applied to study the growth kinetics of passive oxide films on iron and stainless steel substrates in pH 8.4 borate buffer solution. Under electrical potential from 0 to 800 mV, the growth rate of oxide films decreases exponentially in thickness following the direct logarithmic growth law predicted in the point defect model. The electric field in the oxide on iron is independent of the applied potentials consistent with the point defect model. In stainless steel, however, the electric field depends strongly on the applied potential indicating that the oxide properties change as the applied potential varies.

We have used ultra-small-angle scattering (USANS) and fluorescence microscopy to show the existence of large-scale structure in attractive colloidal glasses composed of block polyelectrolyte micelles. Our systems display evidence of surface scattering, with the scattered intensity I at low scattering vector q scaling as I ∼ qx with x in the range –3 to –4. We believe this is due to surface scattering from large, highly polydisperse aggregates with rough interfaces. USANS may provide an ideal way to distinguish fractal colloidal gels and colloidal glasses.

In this article we describe how we have used the pair distribution function of zeolites to solve complex structural problems. A first study was dedicated to refining the structure of disordered zeolite beta, a zeolite that is used in the alkylation of benzene. A second study is a work in progress geared toward the determination of the mechanism of negative thermal expansion of zeolite chabazite, which has been found to be one of the most contracting materials known. Preliminary results suggest that the individual Si-Ox distances and Ox-Si-Ox angles in the tetrahedral are deformed with temperature while the average tetrahedra dimensions stay constant.

Hydrating tricalcium and dicalcium silicate mixtures were studied using time-resolved quasielastic neutron scattering. Application of a hydration model allowed the extraction of several parameters describing the hydration mechanics. The hydration rate during the nucleation and growth period, diffusivity during the diffusion limited regime, and the maximum amount of product able to be formed were not related linearly to the mixture combinations. Addition of dicalcium silicate at approximately 20 wt. % caused a sharp alteration to these parameters, including reduced hydration rate and reaction layer permeability. These two factors lead to the prediction that more reaction products would be ultimately manufactured during the reactions at this composition.

In-situ, time-of-flight neutron diffraction was performed to investigate the martensitic phase transformation during quasi-static uniaxial compression testing of 304L stainless steel at 300K (room temperature) and 203K. In-situ neutron diffraction study enabled the bulk measurement of intensity evolution for each hkl atomic plane during the austenite (fcc) to martensite (hcp and bcc) phase transformation. The neutron diffraction patterns show that the martensite phases started to develop at about 2.5% applied strain (600 MPa applied stress) at 203K. However, at 300K, the martensite formation was not observed throughout the test. Furthermore, from changes in the relative intensities of individual hkl atomic planes, the selective phase transformation can be well understood and the grain orientation relationship between the austenite and newly-forming martensite phases can be determined. The results show that the fcc grain families with {111} and {200} plane normals parallel to the loading axis are favored for the “fcc to hcp” and “fcc to bcc” transformations, respectively.

The properties of the NaxCoO2 class of materials are of interest from a number of viewpoints. These compounds are based on a triangular lattice of spin-½ ions—prototype RVB system— where a high thermoelectric-power Curie-Weiss metallic paramagnet is found for Na0.7CoO2, a charge ordered insulator at x=0.5, and a paramagnetic metal where superconductivity is induced in Na0.3CoO2 when it is intercalated with water. Here we briefly review our neutron diffraction and inelastic scattering measurements characterizing the crystal structure and lattice dynamics, and relate these to the observed physical properties. The basic structure of NaxCoO2 is hexagonal and consists of robust layers of CoO2 interspersed by Na layers with two inequivalent sites. Two special cases are x=1 where one of these sites is fully occupied and the other empty, and x=½ where both sites have equal occupancies of ¼ and the system is a charge ordered insulator. For general × the site occupancies are inequivalent and vary systematically with x. In the regime of x=0.75 we find a first-order transition from a high symmetry Na site at low T to a three-fold split site (with lower symmetry) at high T. This transition is first order and varies with x. For the Na0.3CoO2. 1.4(H/D)2O superconductor, the water forms two additional layers between the Na and CoO2, increasing the c -axis lattice parameter of the hexagonal P 63/mmc space group from 11.16 Å to 19.5 Å. The Na ions are found to occupy a different configuration from the parent compound, while the water forms a structure that replicates the structure of ice to a good approximation. We find a strong inverse correlation between the CoO2 layer thickness and the superconducting transition temperature (TC increases with decreasing thickness). The phonon density-of-states for Na0.3CoO2 exhibits distinct acoustic and optic bands, with a high-energy cutoff of ∼100 meV. The lattice dynamical scattering for the superconductor is dominated by the hydrogen modes, with librational and bending modes that are quite similar to ice, supporting the structural model that the water intercalates and forms ice-like layers in the superconductor.

We have developed a scanning, polychromatic x-ray microscopy technique with submicron spatial resolution at the Advanced Photon Source. In this technique, white undulator radiation is focused to submicron diameter using elliptical mirrors. Laue diffraction patterns scattered from the sample are collected with an area detector and then analyzed to obtain the local crystal structure, lattice orientation, and strain tensor. These new microdiffraction capabilities have enabled both 2D and 3D structural studies of materials on mesoscopic length-scales of tenths-to-hundreds of microns. For thin samples such as deposited films, 2D structural maps are obtained by step-scanning the area of interest. For example, 2D x-ray microscopy has been applied in studies of the epitaxial growth of oxide films. For bulk samples, a 3D differential-aperture x-ray microscopy technique has been developed that yields the full diffraction information from each submicron volume element. The capabilities of 3D x-ray microscopy are demonstrated here with measurements of grain orientations and grain boundary motion in polycrystalline aluminum during 3D thermal grain growth. X-ray microscopy provides the needed, direct link between the experimentally measured 3D microstructural evolution and the results of theory and modeling of materials processes on mesoscopic length scales.

An in-situ DC magnetron sputter deposition system was constructed on the goniometer of an X-ray diffractometer for investigation of thin film nucleation and growth in real time. Tantalum films were deposited on silicon and A723 steel substrates under various deposition conditions. This paper showed: 1) Ta films evolved in single or mixed α-Ta and β-Ta phase on Si and Fe with very different growth characteristics. 2) Crystalline phase was sensitive to deposition mechanics, Ta film changed phase spontaneously without external parameter changes. 3) In pressure range 0.65–13 Pa at 100 watts, phase was not sensitive to pressure variations, but deposition rate and degree of texture decreased at high gas pressure. 4) Depositions using heavier gas showed higher a-Ta concentrations. 5) Reverse sputter cleaning of target and substrate surfaces improved Ta film adhesion.

X-ray diffraction was recognized from the early days as highly sensitive to atomic displacements. Indeed structural crystallography has been very successful in locating with great precision the position of atoms within an individual unit cell. In disordered systems it is the average structure and fluctuations about it that may be determined. In the field of mechanics diffraction may thus be used to evaluate elastic displacement fields. In this short overview we give examples from recent work where x-ray diffraction has been used to investigate average strains in lines, films or multilayers. In small objects the proximity of surfaces or interfaces may create very inhomogeneous displacement fields. X-ray scattering is again one of the best methods to determine such distributions. The need to characterize displacement fields in nanostructures together with the advent of third generation synchrotron radiation sources has generated new and powerful methods (anomalous diffraction, coherent diffraction, microdiffraction, …). We review some of the recent and promising results in the field of strain measurements in small dimensions via X-ray diffraction.

Vibrational spectra for single wall carbon nanotubes, double wall carbon nanotubes, single wall carbon nanohorns and C60-peapods have been measured with inelastic neutron scattering in a wide range of energy transfer, 5–220 meV. A decrease in intensity around 75–100 meV and the appearance of two peaks around 120–125 meV and 150 meV in the double wall nanotubes and C60-peapods spectra compared to single wall carbon nanotubes and nanohorns were observed. These findings indicate the possibility of strong interaction between the walls of the double wall carbon nanotube, and between C60 molecules and carbon nanotube of the peapod. Alternatively, a possible contamination of the samples by hydrogen (even in microscopic quantities) covalently bonded to the carbon also can account for the observed phenomena.

The advent of nanocarbons, from single- and multiple-walled nanotubes to nanohorns, avails model studies of confined molecules on the nanoscale. Water encapsulated inside the quasi-one-dimensional channels of these materials is expected to exhibit anomalous behavior due to the unique geometry of nanotubes and the weak interaction between the water molecules and the carbon atoms. We have employed neutron small-to-wide angle diffraction, quasielastic and inelastic scattering in conjunction with molecular-dynamics simulations to characterize the structures and dynamics of water adsorbed in open-ended single- and double-walled nanotubes over a wide range of spatial and temporal scales. We find that a square-ice sheet wrapped next to the inner nanotube wall and a water chain in the interior are the key structural elements of nanotube-confined water/ice. This configuration results in a hydrogen-bond connectivity that markedly differs from that in bulk water. This significantly softened hydrogen-bond network manifests in strong energy shifts of the observed and simulated inter- and intra-molecular vibrations. The very large mean-square displacement of hydrogen atoms observed experimentally and the strong anharmonicity inferred from simulations explain the fluid-like behavior at temperatures far below the freezing point of normal water.