Structural response of crystals to an applied external perturbation is important as a key for understanding microscopic origin of physical properties. Experimental investigation of structural response is a great challenge for modern structure analysis. We demonstrate how advanced X-ray diffraction techniques facilitate probing tiny (10(-4) angstrom) distortions of bond lengths under a permanent electric field. We also discuss details of the experimental procedure essential for reaching such precision. We ask whether the experiment can be used to evaluate chemical bonds in crystals by their sensitivity to an external electric field and discuss if the bond deformations can be predicted using the bond-valence model or the Bader's theory of atoms in molecules and crystals. Finally, we describe the new time-resolved studies of a structural response to a dynamical switch of applied electric field. These results give access to the time-lining of piezoelectric effect on a microsecond time scale.

Sessions C697direction.However, a tilt range of 10° would cover 17.4 % of reciprocal space, and if it is possible to collect high quality diffraction data up to 1Å resolution, this would still be much more than 1 independent reflection per non-hydrogen atom.In contrast to precession electron diffraction (PED) [5] LARBED includes all tilt angles within the limits of the tilt range and thus records diffraction intensities at the Bragg condition for a large range of diffraction conditions.Averaging over all these different Umweg excitations allows one to reconstruct quasi-kinematic diffraction intensities for part of 3D reciprocal space, as shown in Figure 1 for the example of K 2 O•7Nb 2 O 5 [6], in a random [hk0] orientation.K 2 O•7Nb 2 O 5 has space group P4/mbm (No. 127) and unit cell vectors of length a = b = 27.5Å and c = 3.94 Å.The data was automatically acquired using the QED DM-PlugIn by HREM Research [7].Figure 1: a) 3D reciprocal space reconstructed from the data shown in Fig. 2. Because of the tilt range of only ± 4° the missing wedge is rather large.The vertical component spans a range of -0.5 nm -1 ≤ k z ≤ 0.5 nm -1 .The green slices correspond to the vertical cuts through this 3D space shown in b).b) Positions of diffraction spots in 3D reciprocal space at different parallel planes.The intensities are the mean intensities averaged over a large number of diffraction patterns for which the Ewald sphere cut through that voxel in k-space.The contrast has been adjusted to reveal all reflections, not just the very bright ones.(White areas are due to the CCD read-out streak of very intense peaks.)

Recent inelastic neutron and x-ray scattering measurements of lattice vibrations in superconductors revealed exceptionally strong electron-phonon coupling in many materials.In the cases of conventional superconductors, it is well described by standard theory; in copper oxides it is entirely unexpected.One can take advantage of this strong electron-phonon coupling to investigate electronic charge degrees of freedom by measuring phonon spectral functions.One can obtain detailed information of the superconducting gap as well as the competition between charge density wave and superconductivity.The talk will survey recent results beginning with conventional strongcoupling superconductors YNi 2 B 2 C and NbSe 2 , then moving on to unusual charge fluctuations that renormalize bond stretching phonons in cuprate superconductors.

Time-resolved measurements of the macroscopic and microscopic strains in piezoelectric crystals were performed with a novel data acquisition technique implemented on the basis of a field programmed gate array system. Both types of strains were induced in a crystal by an applied periodic high voltage with fast (within 100 ns) switches between opposite polarities and measured simultaneously by respective angular shifts and integrated intensities of synchrotron x-ray diffraction rocking curves. The time resolution achieved with the developed data acquisition system was 100 ns. The paper demonstrates the particular application of this technique for the investigations of time dynamics of lattice constants and atomic positions in a unit cell for piezoelectric BiB3O6 and Li2SO4⋅H2O crystals. It has been found that 100 ns fast rising time of an applied external electric field induces oscillations of the crystal lattice constants, visible as oscillations of Bragg peak angular positions. At the same time, these oscillations are not observed for the Bragg intensities, i.e., for fractional positions of atoms in the unit cell and correspondingly for bond lengths. The results allow suggesting a model for the mutual interconnection between the deformation of bond lengths and lattice constants in piezoelectric crystals.

An external electric field applied to a piezoelectric crystal induces both, a change of the crystal lattice parameters (external strain) and a shift of the atomic positions within a unit cell (internal strain). The first phenomenon results in the macroscopic deformation of a crystal under an external electric field and is known as the converse piezoelectric effect. The second phenomenon is associated with the dielectric polarization of the crystal media. Although both phenomena are well studied on the macroscopic level, there is still a poor understanding of their origin on the atomic scale. Since the last few years the internal strain of different crystals is under intensive investigation using methods of precise X-ray structure analysis and high intensity of the synchrotron radiation beam for measuring the tiny differences of Bragg diffraction intensities with and without an applied external electric field [1] (see Fig. 1). From the study of the relative change in the integrated intensities of different X-ray reflections due to the external electric perturbation it is experimentally possible to obtain the information about the atomic displacements within the unit cell [2]. At the same time the macroscopic homogeneous deformation of the crystal is simultaneously visible as a small shift of the rocking curve position [3].

Piezoelectric lithium sulfate monohydrate, Li2SO4.H2O, was analyzed with respect to the relationship between the static structural properties of the crystal and its response to an external electric field. The static electron density was determined via standard low-temperature X-ray data collection at 90 (5) K using an Enraf-Nonius CAD-4 diffractometer, Mo Kalpha radiation and multipole model refinement. Then a synchrotron-radiation experiment using the D3 beamline at HASYLAB was conducted in order to investigate the structural deformations in Li2SO4.H2O caused by an applied external electric field. In particular, the shifts of Bragg-peak positions induced by the electric field were measured and the piezoelectric constants d211, d222, d233 and d213 of Li2SO4.H2O were obtained from the shifts. With the same experimental setup the variations of more than 100 Bragg intensities were measured under an applied electric field. The data were used to refine the corresponding displacements of individual atoms within the unit cell. The distortions of the cation-anion bond lengths in the LiO4, LiO3(H2O) and SO4 tetrahedra were evaluated and then analyzed in terms of the electron-density-related properties of the Li-O and S-O bonds. The two lithium structural units were found to be strongly deformed by the applied electric field, while the SO(4) tetrahedron changed less. This is in agreement with the low bond strength of the Li-O bonds.

Page s 81difference Patterson for the ID31 data at two wavelengths around the Br K edge and also the Pt LIII edge shows up binding site 1 clearly in one of the six samples tested.In order to investigate the detailed binding behaviour we have conducted single crystal analyses with time-resolved freeze quenching after lysozyme single crystal soak times of 10, 90 and 170 minutes.Whilst the quick soaking of 10 minutes, used in our first experiments at ESRF ID31 above, shows clear binding there is a steady progression of increasing binding strength with increasing soak time.Thus, these timeresolved analytical chemistry results show that further heavy atom signal optimizations, and reproducible behaviour, are possible.Prospects for extending our approach to the yet larger isomorphous and wavelength dispersive signal case of Ta 6 Br 12 bound to lysozyme for powder experiments will also be described.Overall, such multi heavy atom cluster compounds like K 2 PtBr 6 and Ta 6 Br 12 offer a way forward to solve de novo protein structures by powder diffraction.

For the first time electric-field-induced atomic displacements (internal strains) in non-ferroelectric polar BiB3O6 single crystal plates (point symmetry 2) were investigated using X-ray diffraction technique. The intensity variations of selected Bragg reflections were collected for three different orientations of the applied external electric field vector with respect to the crystal lattice and used for calculating the microscopic structural response of BiB3O6. Due to the limited number of the reflections providing measurable changes in Bragg intensities we restricted ourselves in analyzing the shift of the B3O6 sublattice relative to the Bi one. In addition, we considered the deformation of the Bi-O, B(1)-O and B(2)-O bond lengths and identified the [B(2)O-3] group as the most sensitive structural unit to an external electric perturbation.

We have determined all eight components of the piezoelectric tensor of a monoclinic crystal, BiB 3 O 6 , by means of synchrotron X-ray diffraction technique. The experiments have been performed on a four circle goniometer using the ω -scan method introduced by Graafsma [1] which is universal in the choice of appropriate reflections. The determined values of the piezoelectric tensor are in good agreement with those obtained earlier for BiB 3 O 6 with the use of an optical Michelson interferometer.

Crystal structures formed by molecules with similar carbon skeleton but possessing different small substituents have been analyzed.These were naphthalenes, anthracenes, alkanes, and adamantanes.Methyl, hydroxyl, carboxyl, halogen, nitro, cyano and several other groups were regarded as substituents.The Cambridge Structural Database has been used as the main source of information.It was confirmed that arrangements of molecules in crystals affected not only by the chemical nature of substituents itself but also by the number of these and their mutual displacement.Some relations between the presence of particular groups in the definite positions and probable crystal structures of substances have been found.

An external electric field applied to a piezoelectric crystal induces both, a change of the crystal lattice parameters (external strain) and a shift of the atomic positions within a unit cell (internal strain). The first phenomenon results in the macroscopic deformation of a crystal under external electric field and is known as the converse piezoelectric effect. The second phenomenon is associated with the dielectric polarization of the crystal media. Although both phenomena are well studied on the macroscopic level, there is still a poor understanding of their origin on the atomic scale. Since the last few years the internal strain of different crystals is under intensive investigation using methods of precise X-ray structure analysis and high intensity of the synchrotron radiation beam for measuring the tiny differences of Bragg diffraction intensities with and without an applied external electric field [1] (see Fig. 1). From the study of the relative change in the integrated intensities of different X-ray reflections due to the external electric perturbation it is experimentally possible to obtain the information about the atomic displacements within the unit cell [2]. At the same time the macroscopic homogeneous deformation of the crystal is simultaneously visible as a small shift in the rocking curve position [3].