Size/Strain Round Robin


The Report on the first round-robin phase is available.

 

Although your results cannot be accepted any more, it is still possible to download the original measurements. Some of the reasons for initiating the round robin can be found below, and more details about the material and analysis procedures are here.


 

Round-Robin materials

The measurements (the so-called "representative" diffraction patterns) that are available for download were collected at participating laboratories with the intent to include a wide variety of experimental conditions (sealed and synchrotron x-ray, CW neutrons). All the measurements were done on two samples:

Although the first sample selected for the Round Robin shows isotropic line broadening, future samples will exhibit anisotropic line broadening.

CeO2 belongs to the space group Fm-3m with the approximate lattice parameter of a = 5.41 . Atom (ion) positions are as follows:

            Atom         x          y          z

            Ce+4        0          0          0

            O-2        0.25     0.25     0.25

The suggested list of line-broadening methods of analysis is as follows:

 

Data for download

I put data files in three different formats (special thanks to Nita Dragoe who adapted Powder 2 to handle large number of data points – yes, the ESRF measurements):

These three formats cover all the line-broadening methods that will be used. The designation "sh" in file names stands for "sharp" and denotes the "instrumental standard", and "br" denotes diffraction patterns with broadened lines. The recommended value of P for a polarization factor for x-rays, 1 + Pcos22q, is given below for all the data sets. 

The "representative" diffraction patterns can be downloaded by clicking on the links below. 

Laboratory x-ray sources:

 

Synchrotron x-ray sources:

 

Neutron sources (constant wavelength):

 

Neutron spallation source (time-of-flight data):

 

The Organizer,

Davor Balzar, University of Denver and NIST; balzar@boulder.nist.gov

 

 

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The Round-Robin rational

The Commission on Powder Diffraction (CPD) of the International Union of Crystallography (IUCr) is sponsoring a round robin on size and strain effects in materials. The purpose is twofold: (i) Different methods of line-broadening analysis will be compared on the identical sets of measurements; (ii) Reliability of determination of coherent domain size and (micro)strain by different instruments will be tested on an identical set of samples. The results will be published in the open literature and reprints disseminated to the powder-diffraction community. The initiative to organize a Round Robin on Size/Strain goes back to 1998 and the ECM-18 and EPDIC-6 conferences. There is a vast literature on this subject. An insight into some of the problems and definition of basic terminology can be found in recent publications:

Quantification of a specimen's size and strain values requires definition of the analysis method and correction for the instrumental-broadening effects. Even a casual user of some of the line-broadening techniques is aware of systematic and significant differences in results obtained through different approaches. There are literally dozens of different analysis methods that can yield much different or even physically impossible results. The approaches are broadly divided into two groups: model-independent and model-dependent. The former is mainly identified with the Fourier-deconvolution correction for instrumental broadening (Stokes method), which is followed by the Warren-Averbach approximation for the size/strain-effect separation. The latter mainly contains different integral-breadth methods among which some are more widely used and therefore proposed as a part of the Round Robin. Integral-breadth methods are to be preceded by the instrumental-broadening correction, which will depend on a particular method and will be defined accordingly. Furthermore, as Rietveld-refinement programs build in more and more sophisticated line-broadening approaches, they will be used more frequently as a tool for line-broadening analysis.

The list of methods to be used by Round-Robin participants is given above. It was planned that the "representative" diffraction patterns be sent to the Round-Robin participants. The "representative" designation has at least twofold connotation: First, diffraction patterns is  collected with different radiation and geometry (sealed and synchrotron x-ray, CW neutrons). Second, it is of utmost importance for a successful Round Robin on methods of line-broadening analysis to have high-quality data without substantial systematic errors. The list of facilities where "representative" diffraction patterns were collected is given above.

 

Download the Round-Robin data

 

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Last revised: April 12, 2001