High-energy photon diffraction is used to investigate the charge ordering previously studied by neutron diffraction in La1.48Nd0.4Sr0.12CuO4. Besides confirming the existence of superlattice peaks due to charge order, the temperature dependence of the peak intensity, width, and position has been determined with improved precision. Furthermore, we show that the scattered intensity has a sinusoidial modulation along c * , consistent with long-range Coulomb interactions between ordered charges within the CuO2 planes.

Superstructure reflections due to the ordering of holes into stripes in La1.45Nd0.4Sr0.15CuO4 have been studied with high energy x-ray diffraction. These reflections have been observed clearly for the first time in a sample which is superconducting at low temperatures (Tc ∼ 10 K). The stripe peaks vanish above 62(5) K whereas the magnetic signal of the stripe ordering which has been seen with neutrons before is already suppressed at ∼ 45 K. Our results confirm that the ordering of spins and holes is driven by the charges as it is found in the case of La1.6−xNd0.4SrxCuO4 at the doping level of x = 0.12.

High energy x-ray diffraction is used to investigate the bulk oxygen ordering properties of YBa2Cu3O6+x. Superstructures of Cu-O chains aligned along the b axis and ordered with periodicity ma, along the a axis have been observed. For x < 0.62 the only observed superstructure is ortho-II with m = 2. At room temperature we find ortho-III (m = 3) for 0.72 ≤ x ≤ 0.82, ortho-V (m = 5) in a mixed state with ortho-II at x = 0.62, and ortho-VIII (m = 8) at x = 0.67. Ortho-II is a 3D ordered structural phase, the remaining ones are essentially 2D. None of the superstructures develops long range ordering. Studies of the ortho-II ordering properties in samples prepared with x = 0.5 but by different methods show that finite size domains with internal thermodynamic equilibrium are formed. The crystal perfection as well as the thermal annealing history determine the domain size. The temperature dependence of the observed superstructure ordering is investigated explicitly and a structural phase diagram is presented.

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The large penetration power of high-energy X-rays (>60 keV) raises interesting prospects for new types of structural characterizations of polycrystalline materials. It becomes possible in a nondestructive manner to perform local studies, within the bulk of the material, of the fundamental materials physics properties: grain orientations, strain, dislocation densities etc. In favourable cases these properties may be mapped in three dimensions with a spatial resolution that matches the dimensions of the individual grains. Imbedded volumes and interfaces become accessible. Moreover, the high energies allow better in-situ studies of samples in complicated environments (industrial process optimization). General techniques for research in this energy range have been developed using broad-band angle-dispersive methods, on-line two-dimensional detectors and conical slits. Characterizations have been made at the level of the individual grains and grain boundaries as well as on ensembles of grains. The spatial resolution is presently of the order of 10-100 I, tm. Four examples of applications are presented along with an outlook.