The structure analysis using program MAUD

Martin Kusý

Ústav Materiálov, J. Bottu 23, 917 23 Trnava, Slovenská Republika

e-mail: martin.kusy@stuba.sk

The structure determination from powder diffraction data using the Rietveld approach is in most cases tedious work. However, due to suitable software available long lasting calculations can be significantly shortened. Currently, variety of computer programs for this purpose is available either as freeware or on a commercial base. Nevertheless, the degree these programs help user in extracting the structural data may vary significantly. The shared computer programs based on the Rietveld method can be divided into two general categories from the point of processing basic Rietveld refinable parameters. First category contains number of examples of programs which provide user with a value of refined parameters, for example GSAS, DBWS or FullProf. On the other hand only few programs are available which directly list values of structural parameters determined after each refinement cycle. One of them is a Rietveld method based computer program MAUD.

Both approaches have advantages as well as drawbacks. The first group of programs necessarily needs to employ further processing of extracted parameters. On the other hand it means also opportunity for operator to treat and manipulate the raw parameters in order to extract specific structural information. Second group offers instant information about structural parameters which are considered as refined values. However, these are provided without possibility to interact with basic parameters known from the Rietveld approach. Certainly, number of supporters can be found for both categories of programs. This contribution is not aimed at finding the best group of programs. It would rather concentrate and highlight some of valuable functions and properties the computer program MAUD offers to an operator.

Maud – stands for Materials Analysis Using Diffraction is diffraction/reflectivity analysis program developed on the basis of Rietveld method by Luca Lutterotti from University of Trento in Italy. This program is available since 1997. Maud is written in Java and can be executable in Windows, Mac OSX, Linux or Unix with pre-installed Java VM 1.4.

Author summarized the main features of the Maud program as follows:

• Easy to use, every action is controlled by a GUI
• Works with X-ray, synchrotron, Neutron, TOF
• Developed for Rietveld analysis, simultaneous multi spectra and different instruments/techniques supported
• Ab-initio structure solution integration, from peak finding, indexing to solving
• Different optimization algorithms available (LS, Evolutionary, Simulated Annealing, Metadynamics)
• Le Bail fitting
• Quantitative phase analysis
• Microstructure analysis (size-strain, anisotropy and distributions included)
• Texture and residual stress analysis using part or full spectra
• MEM algorithm for Electron Density Maps and fitting
• Thin film and multilayer aware; film thickness and absorption models
• Reflectivity fitting by different models, from Parratt (Matrix) to Discrete Born Approximation
• Several data files input formats
• Works and input images from 2D detectors (image plates, CCD)
• CIF compliance for input/output; import structures from databases

Our experience with the structure analysis of bulk steels or steel powders usually leads to application of quantitative phase analysis, microstructure analysis, texture analysis. In case of coated steel sheets, film thickness was determined successfully.

Due to simple user interface and available wizard the quantitative phase analysis can be performed using Maud in an intuitive way via releasing set of refinable parameters in five easy steps. Advanced users have opportunity to control each parameter separately.

For the purpose of microstructure analysis, Maud allows to use isotropic Delf model, anisotropic models with no rules and anisotropic model with Popa rules. Warren models for antiphase boundary and planar defects are also implemented in the code.

User can find also effective tools for compensation the texture of material. For this purpose, models such as March-Dollase, Harmonic functions, E-WIMV, WIMV are available. Experience shows that in most cases harmonic functions tends to be effective only when fiber symmetry as simplest one is engaged. The lower the symmetry the more of unstable parameters usually appears. E-WIMV and WIMV modules, allows the texture to be determined using Beartex from texture measurements and imported afterwards. Bearing in mind the drawback of harmonic functions to import data from Beartex appears to be a safest way of texture compensation.

The Maud program provides user effective tool to characterize layers or multilayers deposited on single or multiphase substrate with possibility of thickness determination. For this purpose, the expected structure, phase constitution, ordering of layers and thickness is designed via available program interface. All mentioned layer properties can be during program execution handled as refinalbe parameters.

The Maud program is effective tool for structure analysis using diffraction. In general, it offers user friendly interface with the real-time pattern refinement monitor. Wider application of this program in scientific community is probably hindered with fact that there is no user guide available at the moment. Existing tutorials, Maud forum and Download section can be found at http://www.ing.unitn.it/~maud/index.html.

L. Lutterotti, S. Matthies and H. -R. Wenk, "MAUD (Material Analysis Using Diffraction): a user friendly Java program for Rietveld Texture Analysis and more", Proceeding of the Twelfth International Conference on Textures of Materials (ICOTOM-12), Vol. 1, 1599, (1999)

Acknowledgement

Financial support of the Slovak Grant Agency VEGA provided to project 1/4107/07 is acknowledged.