Olivier Masson

A high-resolution X-ray diffractometer for the study of imperfect materials

A high-resolution X-ray diffractometer devoted to the study of imperfect materials (mainly oxides and ceramics) is presented. It is based on a rotating anode generator, a four-bounce monochromator, a five-movement sample holder and a curved position-sensitive detector (PSD). This setup allows rapid acquisition of a reciprocal-space map (in less than 10u2005h) even for very poorly diffracting materials. The two-dimensional instrumental profile is calculated taking into account each optical element in the beam path. The one-dimensional instrumental profiles corresponding to widely used scans (ω scan, θ–2θ scan, rocking curve and powder scan) are also calculated. In the three former cases, the setup exhibits an excellent angular resolution (0.003°), whereas in the latter case the resolution is lowered by one order of magnitude at the benefit of a strong increase in the collected intensity. The possibilities of this diffractometer are illustrated with three examples: an epitaxic layer, a microstructured single crystal and a powder.

Reflection Asymmetric Powder Diffraction with Flat-Plate Sample using a Curved Position-Sensitive Detector (INEL CPS 120)

The reflection flat-sample asymmetric geometry is an attractive set-up for powder diffraction measurements, as compared to either conventional Debye–Scherrer or symmetric Bragg–Brentano geometries. Combined with grazing- or fixed-incidence-angle X-rays, it is suitable for surface-structure or thin-film texture analysis. Furthermore, it allows curved position-sensitive detectors to be used for in situ experiments. In this paper, the major systematic error sources in connection with this geometry are reviewed. It is confirmed that experimental linearization of the curved position-sensitive detector and sample positioning have to be very carefully performed. Simple and automatable procedures are proposed. Then, it is shown that peak-location accuracy leads to satisfactory cell-parameter determination as checked by the use of a silicon international standard reference sample and that structure refinement by the Rietveld method can be performed in very good conditions, as observed with an NaBi2Sb3O11 compound.

A new method for the determination of strain profiles in epitaxic thin films using X-ray diffraction

A new and versatile method is proposed for the determination of strain profiles in epitaxic thin films. It is based on the simulation of the X-ray diffraction (XRD) profiles using cubic B-spline functions to model the vertical lattice displacement profile. The lattice displacement profile, and consequently the strain profile, directly results from a least-square fit of the model to the experimental XRD profiles. No a priori assumption is made regarding the shape of the strain profile. Moreover, as spline functions are used, the recovered lattice displacement profile is smooth and exhibits a minimum curvature, thus avoiding oscillating or saw-toothed unphysical solutions. The potential of this method is illustrated with (100) yttria-stabilized zirconia epitaxic thin films deposited onto (11bar{2}0) sapphire substrates by sol–gel processing.

Microstructural analysis in epitaxial zirconia layers

Abstract Y2O3 stabilised ZrO2 (YSZ) layers were deposited on (1 1 2 0) Al2O3 by sol–gel dip-coating. A low temperature heat treatment produces a polycrystalline film. Further heating at 1500xa0°C yields an epitaxial layer by grain growth of the islands with the lowest interfacial energy. We used a home-made high resolution diffractometer to record reciprocal space maps of the YSZ layer. The simulation of the diffraction profiles with a kinematical scattering model enables us to extract the strain profile within the layer, the average thickness and the vertical island size distribution.

Miscut angles measurement and precise sample positioning with a four circle diffractometer

A method is derived for precise sample positioning with a four circle diffractometer. The sample can be oriented either with respect to a crystallographic plane or with respect to the sample surface with an accuracy of about 0.001°. The miscut angles can be easily deduced with an accuracy of a few 1/1000°.

On the use of one-dimensional position sensitive detector for x-ray diffraction reciprocal space mapping: Data quality and limitations

A homemade x-ray diffractometer using one-dimensional position sensitive detector (PSD) and well suited to the study of thin epitaxial layer systems is presented. It is shown how PSDs can be advantageously used to allow fast reciprocal space mapping, which is especially interesting when analyzing poor crystalline and defective layers as usually observed with oxides and ceramics films. The quality of the data collected with such a setup and the limitations of PSDs in comparison with the use of analyzer crystals are discussed. In particular, the effects of PSD on angular precision, instrument resolution and corrections that must be applied to raw data are presented.

Modelling of line profile asymmetry caused by axial divergence in powder diffraction

A procedure is presented for modelling the axial divergence aberration profile, taking into account all second-order and end effects of the diffractometer system. It is shown that relatively simple calculations, which could be introduced into Rietveld refinement programs, allow the instrument line profile to be modelled accurately at low and high scattering angles. This model compares well with ray-tracing calculations and can give better results than the usually used model proposed by Van Laar & Yelon [J. Appl. Cryst. (1984), 17, 47–54] and Finger, Cox & Jephcoat [J. Appl. Cryst. (1994), 27, 892–900].

Nonlinear optical properties of TeO 2 crystalline phases from first principles

We have computed second and third nonlinear optical susceptibilities of two crystalline bulk tellurium oxide polymorphs:

Theoretical third-order hyperpolarizability of paratellurite from the finite field perturbation method

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Experimental investigation and thermodynamic evaluation of the C–O–Zr ternary system

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