This paper describes experiments carried out at three neutron sources in which Bragg reflection peak profiles of samples of copper, nickel and iron were investigated as a function of plastic strain. All peaks were well fitted by Gaussian functions for true strains of upto 0.25. Peak widths of all samples were found to be simple power law functions of strain and independent of measurement direction. This suggests that use could be made of data gathered in standard residual elastic stress measurements to simultaneously estimate plastic strains.

Using neutron diffraction, we have measured the elastic phase strains of Al/TiC and Al/SiC composites under uniaxial tensile loading. The phase strains were used to reconstruct the global elastic strain. It has been found that, above macroscopic yield, the global elastic strain response is not linear. A theoretical model shows that the nonlinearity is dictated by changes in the ratio of longitudinal phase stresses. Furthermore, the changes in this ratio resulting from matrix plasticity and reinforcement fracture are different which leads to distinct slope changes in the global elastic strain response that can be used to distinguish the onset of these two processes on the global elastic strain loading curve.

Asphaltic materials are used as binders for road asphalts. Such materials have been found to contain a dispersed phase of colloidal particles in the size range of 50-100 Å, according to small angle X-ray scattering(SAXS) techniques. The presence of this dispersed phase has a significant influence on the rheological properties of these materials. These colloidal particles can be isolated by precipitation with heptane, and so they are associated with the well-known asphaltene solubility class in some manner. In this work we review previously published results that suggest that at least part of the asphaltenes are surface active agents in certain solvents such as toluene, or pyridine, and can form micelles in these solvents. Small angle neutron scattering (SANS) indicates the micelles are spherical with average radii in the 50-100 Å range. There is a polydispersity of sizes. The micelles do not grow in these solvents with increasing concentration in the range of 1-10 wt.%, nor do they dissociate on heating to ~ 170 °C. At higher concentrations, however, a more complicated structure develops. The micelles aggregate to form a large cluster composed of micelles. The fractal dimension of the clusters is found to be 1.8.

A major part of the infrastructure is constructed of Portland cement concrete. Nevertheless, many aspects of this material are still not well understood. The main constituent of hydrated Portland cement is a hydrous gel, with significant features on the nanometer scale, that tends to be unstable under vacuum. It is difficult to investigate with conventional instrumental methods. Neutron scattering methods possess unique capabilities to characterize cementitious materials and thus to resolve a number of long-standing issues. Among the applications, quasi-elastic neutron scattering is used to follow non-destructively the progress of the main hydration reaction and to determine the distribution of the water content among the various states: i.e. free, chemically bound, or physically trapped in the gel network. Quasi-elastic neutron scattering can also be applied to investigate the process of ice formation in the pore spaces. Neutron diffraction has been used to observe the development of hydrous phases as a function of time. Small-angle neutron scattering (SANS) proves to be well-suited to the characterization of the microstructure. This method is being used to determine the surface and volume fractal dimensions of the gel as a function of time and as a function of additives such as fly ash or silica fume. In addition, SANS has been applied to characterize silica aggregates for the potential for deleterious reactions in highly alkaline concrete. Aside from their application to specific problems, the combination of neutron scattering techniques is leading to new interpretation of the fundamental structure of the Portland cement gel.

Small angle neutron scattering (SANS) has been used to examine hydrated cement pastes with water-to-cement ratios between 0.25 and 0.8 and cured for 28 days. Various methods of data analysis are applied to the pastes.

Fitting the entire SANS spectra of the hydrated cement paste has suggested that there are two scattering entities in the paste. There is some evidence to suggest that one scattering entity is globules of calcium silicate hydrate formed in the hydrated paste.

The effect of contrast matching in ordinary Portland cement (OPC) and pure C3S has been investigated as a function of time after hydration using the 1-D small-angle scattering technique. The observed scattering response of OPC hydrated with 100% D2O increased in time, while the response of OPC hydrated with a null water mixture did not. The increase in scattering is therefore attributed to the formation of bubbles in the water-filled pores of the hydrating cement paste. The addition of 1% CaCl2 to OPC increased the kinetics of bubble formation considerably. Based on similar contrast measurements, we have concluded that bubbles do not form in pure C3S. However, the addition of 1% CaCl2 was found to induce bubble formation in the hydrated C3S compound.

Neutron powder diffraction data from phase-pure cement compounds has been used to develop structural models suitable for profile refinement of cements. These models were then applied to the determination of cement compound phase abundance in clinkers. This paper reports on the results of clinker phase analysis by powder neutron diffraction and summarizes the results of the refinements of neutron diffraction data from phase-pure cement compounds. The profile refinements provide generally good agreement with cement compound phase abundance measurements of NIST reference clinker specimens by chemical, optical and X-ray methods.

Quasi-elastic neutron scattering provides detailed information of the atomic and molecular interactions responsible for a material's properties and is a direct and nondestructive method of measuring the motion of hydrogen. This technique was utilized to evaluate the state of water in a cementitious material. The relative amount of freezable water that existed in a saturated type I portland cement paste with water/cement ratios of 0.3, 0.4, and 0.5 was determined over a temperature ranging from +3 C to - 40 C. The amount of frozen water relative to the total water content was related to the water filled pore size predicted to be freezable at each temperature. The proportion of immobilized water increased for all water cement ratios gradually with decreasing temperatures below 0 C until most of the water was immobile at -40 C. The relative proportion of immobile water at 3 C was found to be inversely related to the water/cement ratio, which suggested a smaller fraction of large pores for small water/cement ratios. The findings also suggested the immobilization water was independent of water/cement ratio for pores smaller than 15nm.

Small angle scattering data are traditionally interpreted in terms of scattering patterns at the Porod and the Guinier limits. It is difficult to fit the entire scattering pattern to account for scattering from spheres because Rayleigh's formula contains oscillatory terms which are smeared out in practice by perturbations in the sizes of the scattering agents.

It is proposed that a Lorenztian type function be used instead of Rayleigh's function. By using this equation it is possible to fit the entire small angle scattering pattern and obtain the correct forms of the Guinier and Porod limits.

The effects of correlation and multiple scattering are also explored.

This paper briefly describes the chemistry and structures of known copper oxide superconductors as of November 1994. A tabulation of the unique, reliably superconducting cuprates is presented, with year of discovery, as is a simple classification scheme. Recent trends in new materials research are described.

The Zn substitution on Cu(2) sites in YBa2(Cu1-yZny)3O6+x materials is most probably limited to yzn ≈ 0.04. Results of neutron diffraction associated with NMR and μ+SR results reveal ; i) a lowering of TN in the pure AF region x≤0.20 due to a dilution effect of the antiferromagnetic lattice by a static non magnetic impurity, ii) the existence of a non conventionnal magnetic behavior within the intermediate region x≥0.35 characterized by an unusual temperature dependance of magnetic intensities, a reentrancy and the existence of diffuse magnetic scattering (this region is much broader in oxygen composition for Zn-doped than for pure YBCO),iii) an unusual spin dynamics in the "doped A-F phase" which corresponds to a coupling of magnetic excitations to the hole dynamics.

One of the 30 meter small-angle neutron scattering spectrometers at NIST has been used to measure the scattering from YBa2Cu3O7 and Bi2Sr2CaCu2O8 at a range of temperatures from 35 K to 135 K with wavevector transfers Q from 0.01 Å-1 to 0.08 Å-1. Considerable attention was paid to sample preparation in order to reduce the background scattering from crystalline defects and stoichiometric variations in the sample. For both materials, the difference in the differential scattering cross-sections at the critical temperature Tc and at temperatures of Tc ± 20 K showed considerable structure in Q, corresponding to spatial variations in the neutron scattering potential with Fourier components of wavelength of the order of 100 Å.

We describe the use of neutron powder diffraction for studying the local structure of high-temperature superconductors. This is accomplished by carrying out a pair distribution function (PDF) analysis. This approach does not presume a periodic structure and allows short range deviations from perfect crystalline order to be observed. Data from a sample of La2CuO4 collected on two different diffractometers are compared to determine the degree of reproducibility of the results. It is found that the data reproduce very well; however, a model-PDF, fit to the data assuming the average crystal structure in the low-temperature-orthorhombic (LTO) phase, differs from the data in a number of significant ways. This is related to earlier observations that the local structure of the La1.875Ba0.125CuO4 compound differs from the average crystal structure.

L3-x-ray absorption spectroscopy is used together with inelastic neutron scattering and magnetic susceptibility measurements to characterize the Tb oxidation state and bonding in the high-Tc related materials Y1-xTbxBa2Cu3O7 and Pb2Sr2TbCu3O8. The Tb is found to be essentially trivalent in both compounds with no indications of significant hybridization. However, there is evidence of significant Tb-Tb magnetic interactions in Pb2Sr2TbCu3O8 that persist to temperatures much higher than the Tb long-range ordering temperature.

Inelastic neutron scattering (INS) results on the intermultiplet transitions J=0 → 1 and J=1 → 2 in optically opaque EuBa2Cu3O7 are reported. Whereas these multiplets are split by the crystalline electric field (CEF), their low J values are influenced to first order only by the second-order (J=1) and additional fourth-order (J=2) CEF parameters. and the spinorbit coupling parameter were obtained by fitting the splitting of the J=l multiplet and the energy separation between the J=0 and 1 multiplets. The J=0 → 1 splitting observed here is smaller than previously seen by optical spectroscopic studies on a variety of transparent, ionic compounds, necessitating fitting of the free-ion parameter. Additional spectroscopic information on the J=2 multiplet indicates that additional fitting of free ion parameters must be included to adequately model the observed low energy separation between the two lowest J-multiplets. Preliminary calculation on the Q-dependence of the CEF split J=0 → 1 transitions and the comparison with observations are presented.

Statistical information on the phonon frequency spectrum of materials can be obtained by neutron transmission techniques if they contain nuclei with low energy resonances, narrow enough to be Doppler-broadened. We have carried out measurements using this technique for the doped 2-1-4 system, La2.xBaxCuO4. Two samples with slightly different concentrations of barium, one superconducting, the other not, were examined. Pure Lanthanum Cuprate was also studied. Neutron cross section measurements have been made with high energy resolution and statistical precision on the 60m flight path of LANSCE, the pulsed spallation neutron source at Los Alamos National Laboratory. Measurements on all three materials were made over a range of temperatures from 15K to 300K, with small steps through the critical temperature region near 27K. No significant changes in the mean phonon energy of the lanthanum atoms were observed near the critical temperature of the super-conducting material. It appears however that the mean phonon energy of lanthanum in the superconductor is considerably higher than that in the non-superconductors.

NiB, monoclinic Ni4B3, Ni2B and Ni3B were prepared by arc-melting and their roomtemperature crystal structures were refined by Rietveld analysis of neutron powder diffraction data. The NiB refinement is altogether new data. Although the B atoms in NiB form characteristic zigzag chains, the primary coordination of each atom by atoms of the other kind is similar and distinctively sevenfold, with one short (2.117 Å), two intermediate (2.152 Å), and four long (2.163 Å) bonds. Other samples with stoichiometries (YC)nNi2B2, n = 3, 4, did not yield single-phase material, but both x-ray and neutron powder diffraction suggest that the n = 4 structure is present in both of these samples. Phase-pure samples of these homologues may require non-stoichiometry and a more controlled thermal history than is attainable by arc melting.

The nuclear and magnetic structures of HoNi2B2C have been investigated by neutron powder diffraction at room temperature and at 10, 5.1 and 2.2K. The compound crystallizes with the symmetry of space group 14/mmm and has room temperature lattice parameters a=3.5170(1) and c=10.5217(3) Å. No phase transitions of the nuclear structure have been observed in the range of temperatures examined. Magnetic peaks begin to appear at about 8K. The magnetic structure is the superposition of two configurations, one in which ferromagnetic sheets of holmium spins parallel to the a-b plane are coupled antiferromagnetically along the c-axis, and another in which the ferromagnetic planes are rotated away from the antiparallel configuration to give an incommensurate helicoidal structure with a period approximately equal to twelve times the length of the c-axis. The helicoidal structure competes with superconductivity while the antiferromagnetism coexists with it.

Single crystal neutron diffraction techniques have been employed to study the evolution of magnetic structures in RNi2B2C compounds in an attempt to understand the relationship between magnetic ordering and superconductivity in several members of this series. For HoNi2B2C, below the superconducting transition (Tc = 8 K), an incommensurate magnetic structure characterized by two wave vectors (0.585 a* and 0.915 c*) is found in a narrow temperature range between 4.7 K and 6 K. This is the same temperature range where bulk measurements find a deep minimum in the upper critical field, Hc2. Below 4.7 K, HoNi2B2C is a simple collinear antiferromagnet. ErNi2B2C (Tc = 11 K) orders in an incommensurate modulated antiferromagnetic state characterized by an ordering wave vector 0.553 ā * below 7 K, which coexists with superconductivity.

Anisotropic, temperature dependent magnetization measurements on single crystals of HoNi2B2C indicate that there is a cascade of magnetic transitions in zero and low applied magnetic fields. Comparison of the temperature dependence of the specific heat and d(χT)/dT data shows a remarkable agreement in the low field limit, supporting the use of d(χT)/dT as a method of determining the magnetic transition temperatures as a function of applied field. The magnetic transition temperatures determined by this analysis are remarkably sensitive to the applied field and highly anisotropic. Comparison to similar data for ErNi2B2C show that the sensitivity and anisotropy are common features. These data emphasize the importance of anisotropic measurements of field dependent properties on single crystal samples, since the application of a magnetic field to a polycrystalline sample will effectively broaden the transition temperatures.