Simultaneous dynamic electrical and structural measurements of functional materials

A new materials characterization system developed at the XMaS beamline, located at the European Synchrotron Radiation Facility in France, is presented. We show that this new capability allows to measure the atomic structural evolution (crystallography) of piezoelectric materials whilst simultaneously measuring the overall strain characteristics and electrical response to dynamically (ac) applied external stimuli.

The structure and low-energy phonons of the nonferroelectric mixed perovskite: BaMg₁/₃Ta₂/₃O₃

The structure of BaMg(1/3)Ta(2/3)O(3) (BMT) has been studied using x-ray scattering. The phonons have been measured and the results are similar to those of other materials with a perovskite structure such as PbMg(1/3)Nb(2/3)O(3) (PMN). The acoustic and lowest energy optic branches were measured but it was not possible to measure the branches of higher energy, possibly this is because they largely consist of oxygen motions. High-resolution inelastic measurements also showed that the diffuse scattering was strictly elastic and not directly related to the phonon spectra. Diffuse scattering was observed in BMT near the (H ± 1/2, K ± 1/2, L ± 1/2) points in the Brillouin zone and these had a characteristic cube shape. This arises from ordering of the B-site ions in BMT. Additional experiments revealed the diffuse scattering in BMT similar in shape to Bragg reflections at wavevectors of the form (H ± 1/3, K ± 1/3, L ± 1/3). Such reflections were also observed by Lufaso (2004 Chem. Mater. 16 2148) from powders and suggest that this structure of BMT consists of four differently oriented domains of a trigonal structure and results from a different ordering of the B-site ions from that responsible for the scattering at the (H ± 1/2, K ± 1/2, L ± 1/2) points. The results lead us to suggest that for BMT single crystals the bulk has the properties of a cubic perovskite, whereas the surface may have quite different structure from that of the bulk. This difference resembles the behaviour of cubic relaxors like PMN and PMN doped by PbTiO(3), where significant surface effects have been reported.

The use of synchrotron X-rays to observe copper corrosion in real time

We have developed and tested two complementary methods for making time-lapse synchrotron X-ray diffraction (XRD) measurements of the growth of synthetic corrosion layers using a protocol for producing copper(I) chloride (nantokite), on copper as a test. In the first method, a copper coupon was spin-coated with saturated copper(II) chloride solution in air while the surface was characterized in real time using XRD with a fast one-dimensional (1-D) detector. In the second, a droplet of the same reagent was suspended from an X-ray-transparent window in a hermetically sealed cell and the coupon was brought into contact with this while XRD diffractograms were acquired with a charge-coupled device (CCD) camera. The protocol is completed by a deionized water rinse, which was also studied. The XRD shows nantokite precipitation in solution as well as growth on the surface, but the end products were variable proportions of nantokite, cuprite (Cu(2)O), and paratacamite (Cu(2)(OH)(3)Cl). The latter two were observed forming in a reaction between the nantokite and the rinsing water. Comparisons between samples analyzed in the synchrotron and at lower power densities show that the effects of any radiolysis or slight heating of the sample are insignificant in this case. It would be simple to extend these methods to other corrosion or surface reaction systems.

Dipolar excitations at the LIII x-ray absorption edges of the heavy rare-earth metals

We report measured dipolar asymmetry ratios at the LIII edges of the heavy rare-earth metals. The results are compared with a first-principles calculation and excellent agreement is found. A simple model of the scattering is developed, enabling us to reinterpret the resonant x-ray scattering in these materials and to identify the peaks in the asymmetry ratios with features in the spin and orbital moment densities.

Performance of phase plates on the XMaS beamline at the ESRF

Two phase plates, a 0.78 mm-thick natural diamond and a 0.3 mm-thick synthetic diamond, were used to convert linearly polarized X-rays into a circularly polarized beam, to cover an energy range of 3-9 keV. The performance of these plates followed theoretical predictions as indicated by polarization analyses and X-ray magnetic circular dichroism measurements. The use of the device is illustrated by resonant magnetic reflectivity measurements on UAs/Co multilayers.

The XMaS beamline at ESRF: instrumental developments and high-resolution diffraction studies

The beamline, which is situated on a bending magnet at ESRF, comprises a unique combination of instrumentation for high-resolution and magnetic single-crystal diffraction. White-beam operation is possible, as well as focused and unfocused monochromatic modes. In addition to an eleven-axis Huber diffractometer, which facilitates simple operation in both vertical and horizontal scattering geometries, there is an in-vacuum polarization analyser and slit system, mirrors for harmonic rejection, sub 4.2 K and 1 Tesla magnetic field sample environment, plus a diamond phase plate for polarization conditioning. The instrumentation developed specifically for this beamline is described, and its use illustrated by recent scientific results.