Electric field related reduction of the crystalline perfection

It is now more than fifteen years that a Chinese group discovered a surprising fact: the neutron Bragg intensity diffracted by an -LiIO3 crystal can be enhanced by a factor up to 10 under a moderate electric field (102 V/cm). Several groups working with x-rays reported similar facts, not only for a-LiIO3 but also for other crystals (KTP, LiN2H5SO4) which display electric polarisation and one-dimensional ionic conductivity. The x-ray diffraction images ("topographs") show the occurrence, under field, of many lines parallel to the c-axis. In order to explain the observations, a space charge distribution produced by an inhomogeneous one-dimensional ionic conductivity was invoked.

New experimental results obtained at the ESRF ruled out this suggestion: the lines are observed when a field is applied at low temperature (100 K), in spite of the ionic conductivity being reduced by about five orders of magnitude with respect to the room temperature value. Systematic diffraction imaging experiments were undertaken, in alternating electrical field and at low temperature, coupled with electrical measurements on the same samples and temperatures. They allowed us to determine the various phenomena contributing to the reduction in crystalline quality with particular emphasis on the linear images parallel to the polarisation (Figure 53). The electrical measurements give complementary information. All these experiments suggest that the origin of the lines is not the ionic conductivity, but a strongly anisotropic and inhomogeneous polarisation in narrow channels connecting the electrodes.

The main assumption of this "polarised channels" model is that an applied electric field produces locally an additional polarisation with respect to the pre-existing one: the response to an external electrostatic field can concentrate into highly polarised regions rather than polarise the whole crystal. The reason why the crystal can be inhomogeneously polarised is associated with a peculiar feature of the crystalline structure which exhibits, in the KTP case, two additional local minima sites ("holes of potential") for the potassium ions, usually unoccupied. The application of a field along the c axis produces a movement of some potassium ions along their diffusion paths into the "holes of potential" sites, creating in this way additional individual dipoles in the structure. These individual dipoles interact via their associated electrostatic fields, ending in chains of dipoles joining the electrodes. The microscopic «polarised channels» (Figure 54) occur through the collapse of a large number of these chains, which reduces the energy of elastic deformation in the surrounding lattice. The useful information which we can extract from a section topograph under field (15 µm slits set perpendicularly to the c axis) is the number of polarised channels, corresponding to the number of spots, within a unit surface of the film. A crude model allows the average diameter of a polarised channel to be estimated at approximately 6 µm, which appears to be correct when compared to the experimental results.

The gradient of distortion associated with the boundary between polarised and non-polarised regions produces contrast on the X-ray topographs. This deformation introduces the biggest deformation for the (00l) planes while the planes parallel to the c axis are not deformed at all, and there is no modification of the cell parameter c (Figure 55). This is in agreement with what is observed experimentally. The present model implies an accumulation of space charges but these charges are not produced by the inhomogeneous ionic flux. It provides an appropriate explanation of these phenomena for other crystals (as -LiIO3) if "potential holes" exist in their structural channels to allow the construction of the polarised channels.





[1] P. Rejmankova (a), J. Baruchel (a), J. Kulda (b), R. Calemczuk (c), B. Dalce (c), J. Phys. D. Appl. Phys. 28, A 69 (1995)

[2] P. Rejmankova (a), J. Baruchel (a), J. Kulda (b), submitted to Phil. Mag

(a) ESRF

(b) Institute Laue-Langevin, Grenoble (France)

(c) DRF-MC, CEA-Grenoble (France)




Single crystal diffractometry on kaolinite micro-crystals



The structure of kaolinite - a silicate mineral which occurs in sedimentary layers and soils - has been determined principally by powder diffractometry, as sufficiently large and well-ordered crystals for classical diffractometry are not available. For the first time it has now been possible to measure data sets on natural single crystals with volumes down to 0.4 µm3 using the K-goniometer of the Microfocus beamline (ID13). Figure 56 shows an optical image of one of the investigated crystals glued to a glass tip; Figure 57 shows a scanning electron microscopy image of the crystal basal plane.

The data collection was done at = 0.6883 Å by performing - rotations and collecting the reflection patterns with a liquid nitrogen cooled CCD detector developed at the ESRF. The beam size at the sample position was 10 µm. The space group is triclinic and the lattice parameters are a = 5.15 (1) Å, b = 8.94 (1) Å, c = 7.41 (4) Å, = 91.7 (3)0, ß = 104.7 (3)0, = 89.8 (1)0. The lattice parameter determination and integration of intensities was carried out. Preliminary refinements resulted in an unweighted reliability factor of less than 4 % using 453 unique reflections and showed 70 % of the hydrogen atoms.




R. Neder (a), M. Burghammer (a), T. Grasl (a), H. Schulz (a), A. Bram (b), S. Fiedler (b), C. Riekel (b)

(a) Institut für Mineralogie und Kristallographie der LNW, München (Germany)

(b) ESRF




Micro-texture on nickel-iron alloys prepared by electroplating



Artificially patterned structures can be produced by deep etch lithography (the LIGA process). Of current interest is the development of magnetic actuators based on Ni or Ni-Fe alloys. The understanding and control of micro-structure and micro-texture are of considerable importance for technological applications. It has been possible for the first time to perform local texture experiment on rod- and plate-like Ni-Fe alloys with largest dimensions of up to several 100 µm. Figure 58 shows a scanning electron microscopy image of a rod-like sample with a sponge-like morphology at the base.

Diffraction data were obtained with a 10 µm beam at = 0.9 Å using an image plate. Pole figures and inverted pole figures were calculated from the reduced data. The inverse pole figure at three positions along the rod suggests a combination of (111) and (100) fibres close to the growth direction (Figure 59). The inverted pole figure at the base of the rod shows a loss in preferred orientation. This method is also crucial to ascertain texture variations in small electronic devices where performance relies on crystallite orientation and anisotropy.





S. P. Bäckstrøm (a), S. Abel (b), H. Lehr (b), H. R. Wenk (c), C. Riekel (d), J. Appl. Cryst. 29, 118-124 (1996)

(a) SINTEF, Oslom (Norway)

(b) MM Institut für Mikrotechnik GmbH, Mainz (Germany)

(c) Department of Geology and Geophysics, Univ. of California, Berkeley, CA (USA)

(d) ESRF



Local area diffraction on single starch grains



Starch - which is one of the principal food constituants - is made up out polysaccharide chains. Starch granules (Figure 60) - which are stored in plants like wheat or potatoes - are semicrystalline like many polymers. There is an interest in understanding the internal structure and morphology of such granules in relation to storage and transformation during further processing (e.g. cooking).

The sensitivity of starch granules to electron beam irradiation has, however, limited structural studies. It has now been possible to perform scanning diffraction on single starch grains of type A and B of < 50 µm with a ~ 3 µm beam using a glass capillary optics combined with an ellipsoidal mirror on the ESRF Microfocus beamline (ID13). The diffraction pattern of starch disappears in ~ 30 sec which requires the use of an image intensified CCD with video-frequency readout.

On the Microfocus beamline (ID13)




A. Bulcon (a), H. Chanzy (b) and C. Riekel (c), to be published

(a) INRA, Nantes (France)

(b) CERMAV, CNRS, Grenoble (France)

(c) ESRF




The evolution of an ultrasonic strain field followed by diffraction with a 20 ns time resolution



High energy diffraction (E > 100 keV) is well suited for structural analysis of bulk materials. In most cases, both absorption and scattering are small, thus enabling the study of bulk samples with a thickness of several cm. As a benefit of modern synchrotron sources, the high brightness can be exploited to perform measurements in a time-resolved mode with resolutions in the nanosecond range. Exploiting diffraction patterns implies that structural modifications are observed on an atomic level.

Although the detector system was far from being optimised on the High Energy beamline, it was possible to follow the structural response to an external perturbation by high energy X-ray diffraction with a 20 ns time resolution. The time evolution of the strain field of an ultrasound wave with a frequency corresponding to an acoustic wavelength of 1. 14 mm in a Si (111) crystal was followed. High energy radiation at 300 keV probing the bulk is of crucial importance for this case because the strain field vanishes at the surface of the crystal.

Figure 61 shows an intensity map as a function of rocking angle and time. A standing, longitudinal ultrasonic wave is characterised by regions of compression and dilatation with amplitudes varying in time. At a certain moment the sound amplitude is zero and the crystal is free of strain which corresponds to the points of narrowest rocking widths in the figure. Under this condition the crystal behaves like a dynamic scatterer and the integrated diffracted intensity is low. After this zero-crossing point, the regions of antinodes develop, reaching their maximum value a quarter of a period later. Now, the width of the curve corresponds to the maximum strain and the crystal behaves as a kinematical scatterer. The scattering geometry averaged over a large crystal volume including zones of compression and dilatation and thus the whole distribution of lattice planes is seen in a snapshot of time, and the frequency for one sound period of 122 ns seems to be doubled in the figure. The highest peak intensity is obtained at the zero transition of the oscillation since then all lattice planes diffract in the same direction.

This method has several perspectives; among others it could open the possibility for investigating the response in time of critical phenomena if the perturbation by the longitudinal sound wave is applied e.g. close to a phase transition.




K.D. Liss (a), A. Magerl (b), R. Hock (c), A. Remhof (d), submitted to Acta Cryst. A

(a) ESRF

(b) ILL, Grenoble (France)

(c) Mineralogisches Institut, Univ. of Würzburg (Germany)

(d) Ruhruniv. of Bochum (Germany)




In situ, time-resolved X-ray diffraction study of the solid state polymerisation of disulfur dinitride to polysulfur nitride



Polysulfur nitride (SN)x is unique amongst polymeric materials: (SN)x represents a genuine, anisotropic conductor which exhibits a metal-like temperature dependence of the electrical resistivity and shows a superconducting transition at low temperature (Tc < 0.3 K). The compound is usually obtained by spontaneous, thermally induced polymerisation of disulfur dinitride S2N2. Little is known about kinetics and polymerisation mechanism of the title reaction, though a reaction mechanism based on the structures of educt and product has been proposed. Peculiarities of the S2N2/(SN)x system, such as the potential explosion hazard and the preparative challenge associated with handling of the monomer due to its instability and moisture-sensitivity, thus far limited in situ studies of the polymerisation S2N2 -> (SN)x to spectroscopic investigations. X-ray powder diffraction (XRD) employing synchrotron radiation combined with fast read-out detectors and Rietveld refinement, allows time-resolved experiments even for poorly scattering samples. The first in situ study of the solid state polymerisation of S2N2 to (SN)x monitored by XRD is represented here (data have been collected at the Materials Science beamline ID11).

The time-dependent evolution of diffraction patterns during the polymerisation S2N2 -> (SN)x is shown in Figure 62.

The total transformation time for sample masses in the order of 1-2 mg S2N2 amounted to 60 minutes. Thorough analysis of the diffraction patterns of the polymerisation product revealed the presence of two (SN)x phases: -(SN)x and ß-(SN)x in a ratio of about 5 % to 95 %. A micrograph of the polymerisation product, as obtained after breaking a capillary, is displayed in Figure 63.

Chemical reasoning as well as theoretical considerations by Baughman and Chance have led to the proposition that polymerisation of S2N2 proceeds along the crystallographic a-axis. Initial ring opening of one S-N bond of adjacent S2N2 molecules was presumed to result in the formation of intermediate, short-lived radicals. Linear arrays of cleaved S2N2 molecules could thus recombine with little distortion of the molecular planes to directly yield covalently bond (SN)x polymer chains with the observed cis-trans configuration. Data quality allowed for the first time not only to obtain accurate information on the bulk composition of the polymerisation products as well as their variation with time, but also for the following changes of cell parameters during the first 500 s of the reaction; a time interval corresponding to more than 50 % monomer conversion. In fact, a-axis and the angle ß shrank almost linearly by about 1 %, c expanded by around 0.5 %, whereas b and the cell volume remained virtually constant, thus confirming earlier presumptions that the title reaction occurs as a single phase polymerisation.

The unprecedented possibility to refine atomic positions of polymerising S2N2 up to 50 % conversion permitted some insight to be gained into the actual polymerisation mechanism on a molecular scale. However, the experimental accuracy for the determination of atomic positions is less reliable than the standard deviations for the unit cell parameters and thus restricts possible conclusions to the description of qualitative trends.

Summing up, the most important results of this study are:

  • The transformation of S2N2--> (SN)x occurs as a single state polymerisation with auto-catalytic reaction kinetics.
  • The reaction yields a mixture of two structurally related compounds, which explains previous conflicting experimental evidence and is basically the consequence of statistical ring-opening and resultant structural defects.
  • The polymerisation reaction is not accompanied by geometrical changes of the reactant molecules which could point to the presence of a theoretically predicted, excited (singlet) state of S2N2 molecules.
  • The direct conversion of crystalline S2N2 into crystalline (SN)x, the constancy of the cell volume, as well as the retention of the reactant geometry up to high conversion levels, strongly suggest that the title reaction occurs as a martensitic transition.




S. Karhu (a), C. Jouan (a), H. Müller (a), J. Birch (a), A Frost-Jensen (a), S. O. Svensson (a), Å. Kvick (a)

(a) ESRF




Microstructural characterisation of the straining and the ageing of nickel-based superalloy



Single crystal superalloys are used for the high-temperature parts of aircraft engine such as turbine blades. Their good mechanical properties at high temperature are due to the precipitation of an ordered ' phase in a solid solution matrix. Considerable efforts have been devoted in an attempt to improve the efficiency of these materials. Now the major remaining field of research is to determine parameters predicting the rupture in order to optimise the turbine blades lifetime.

During creep at high temperature, the morphology of the ' precipitates evolves from cuboids to a raft-like structure depending on both external and internal stresses. One of the important microstructural parameters for the understanding of the deformation behaviour is the relative mismatch d of the two lattice constants. At the undeformed state and after a standard heat treatment, the /' interfaces are coherent with d10-3 in the case of the superalloy AM1. During a creep test, the rafting of the ' precipitates develops and dislocations produced by plastic strain rearranged into networks at the /' interfaces which contribute to the relaxation of the coherency stresses between rafts.

The high energy X-ray triple crystal diffractometer on ID15A was set up to measure at high temperature the mosaicity and the lattice parameters of an AM1 sample dynamically pre-strained at 900 °C and annealed 20 h at 1050 °C. These measurements are related to the bulk sample and as they are non-destructive, different directions could be analysed.

Figure 64 shows the temperature dependence of the lattice mismatch in parallel and perpendicularly to the applied stress directions. The variation of the lattice mismatch depends strongly on the direction analysed and on the initial deformation state. Its behaviour as a function of temperature provides information on the nature of the /' interfaces and on the distribution of the internal stresses.

Comparing with previous analysis of neutron diffraction experiments, these results show that, under the conditions of the present experiment, the sample was in a metastable state which drives the microstructural change. This microstructural evolution leads to the ageing of the material.

In conclusion, with this type of high resolution measurements, it is now possible to detect and quantify the straining of the material, even in the low deformation range (< 1 %) which is of interest for applications. Such measurements are non-destructive and require no particular surface preparation. They can be performed directly on turbine blades.

In situ temperature measurements of the lattice parameters of an AM 1 single crystal superalloy sample was performed on ID15A. This sample was dynamically pre-strained at 900 °C and annealed at 1050 °C during 20 h. The tensile stress was applied along the <001> direction and the resultant plastic deformation was = 0.6 % (Figure 64).




P. Bastie (a), A. Royer (b), to be published

(a) Laboratoire de Spectrométrie Physique, Grenoble (France)

(b) ESRF




Imaging of weak diffuse scattering phenomena in quasicrystals



Structural investigations of crystalline materials have contributed much to the present day understanding of the solid state. The discovery of quasicrystals (crystalline materials with an altogether different kind of ordering scheme) has extended the traditional concept that crystalline matter is a periodic arrangement of identical units (atoms, cluster of atoms or molecules). The typical quasicrystal is an intermetallic compound in which the building blocks are arranged in a non-periodic but highly ordered way. In fact, the long-range order can be as good as in perfect silicon crystals. Some of these novel materials, e.g. Al-Co-Ni alloys, show even a transition from periodic to aperiodic state and vice versa upon heating. In the course of this transition a rearrangement of atoms takes place which locally can cause disorder. It is one of the fascinating aspects of quasicrystals that they can exhibit perfect long-range order in the presence of short-range disorder. Structural studies are crucial for the understanding of formation and growth, as well as the unusual physical properties of quasicrystals.

X-ray disorder diffuse scattering as a function of temperature is one of the classic tools for analysing disorder in solids. Since the intensity of diffuse scattering is several orders of magnitude smaller than the one of Bragg scattering, an intense synchrotron source such as the ESRF is ideally suited to this type of experiment. Furthermore, the diffuse scattering experiment greatly benefits from the highly parallel beam. Scanning large areas of reciprocal space is most efficiently done with a two-dimensional detector system.

A series of experiments were carried out at the Swiss-Norwegian beamline with a parallel monochromatic beam and the MarResearch imaging plate detector system. Typically, a 1° rotation diffraction pattern could be collected in just 120 seconds (Figure 65). Details of diffuse scattering in quasicrystalline decagonal Al-Co-Ni were visible which had never been observed before. Decagonal Al-Co-Ni has a periodic stacking of layers; the atoms are ordered in a quasi-periodic way within the layers. Local five-fold and ten-fold symmetry is characteristic in the crystal structure, as well as in the corresponding diffraction space (see enlarged detail in Figure 65). On the diffraction pattern, the reciprocal decagonal layers are clearly visible as curved sections; projections of spherical slices onto the 2D detector. The curved sections contain sharp Bragg peaks and diffuse scattering. A first analysis showed that the ordering scheme in decagonal Al-Co-Ni is much more complex than «simple» quasicrystalline ordering. Depending on chemical composition and temperature, orientational ordering of periodic approximate nanodomains, twinned approximate domains on a micrometer scale, ordering of and within columnar clusters are ordering schemes to be considered. This will be further investigated with reverse Monte-Carlo techniques.

The tools for analysing the diffraction data from area detectors are mainly designed for macromolecular applications. At present, software is being developed at the ETH Zürich to tackle materials exhibiting twinning, superstructure effects, non-crystallographic symmetry and diffuse scattering. In particular, imaging of the entire reciprocal space is one of the requirements for quantitative studies of diffuse scattering.




M.A. Estermann (a), W. Steurer (a), P. Pattison (b), H.P. Weber (b), to be published

(a) Laboratory of Crystallography, ETH Zürich (Switzerland)

(b) Swiss-Norwegian CRG, ESRF


Microbeam X-ray diffraction with high lateral resolution applied to a nickel-base super alloy turbine blade after service



In turbine blades subjected to service, changes of the microstructure and a build-up of internal stresses can be observed. The hot regions near the leading and trailing edges are subjected to temperatures up to 1100 °C whereas the regions near the cooling channels are subjected to temperatures of about 800 °C. These temperature gradients cause strong inhomogeneities in the local thermal and mechanical loads. An investigation of the local variations of the internal stresses near the surfaces of turbine blades therefore requires a high lateral resolution which can only be achieved by special techniques. In the present investigation, measurements of line profiles were performed with a new technique, using the advantages of synchrotron radiation at the ESRF, applying the Bragg-Fresnel focusing optics with a spatial resolution of 2 µm x 30 µm (Figure 66).

A turbine blade of the nickel-base super alloy CMSX-6 (provided by the company MTU) which was subjected to service in an accelerated mission test for several hundred hours was investigated at different positions along several (100) and (001) sections. From the locally measured (004) and (400) line profiles the local lattice parameters of the g and ' phases were determined. Figure 67 shows the variation of these lattice constants for the different reflections and phases as a function of the relative distance from the high pressure side up to the low pressure side in the trailing edge region. The analysis of the data shows that in the region near the surfaces i) a macroscopic compressive stress state exists parallel to the surfaces and ii) the higher Al content in this region measured by energy dispersive analysis causes an increase of the net lattice constant. In the bulk of the material a homogeneous stress state exists which is comparable with the results obtained previously.




H. Biermann (a), B.V. Grossmann (a), S. Mechsner (a), H. Mughrabi (a), T. Ungar (b), A. Snigirev (c), I. Snigireva (c), A. Souvorov (c), M. Kocsis (c), C. Raven (c), to be published.

(a) Institut für Werkstoffwissenschaften, Univ. of Erlangen-Nürnberg (Germany)

(b) Institute for General Physics, Univ. of Budapest (Hungary)

(c) ESRF