TOPAS

DIFFRAC.SUITE TOPAS is the latest generation Rietveld software. The basics of the Rietveld method were published in the late 1960´s, when the Dutch crystallographer Hugo Rietveld presented computer based analytical procedures making use of a complete powder diffraction pattern recorded with neutrons.

Basically, the Rietveld method is using analytical profile functions and least-squares algorithms to fit a theoretical to a measured pattern.

Rietveld’s work opened the path to extract detailed crystal structure information from powder diffraction using neutron and X-ray data. These days, the Rietveld method is not only used for structure analysis, but also for the quantification of multi-phase mixtures and the determination of the crystallite microstructure which covers size and strain.

With increasing computer power the Rietveld method became more and more popular even though expert knowledge and case-to-case fine tuning was required. This changed when TOPAS with its Fundamental Parameter Approach was launched in 1999. TOPAS key features to success were to overcome the intrinsic challenges of the Rietveld method:

• Forget about “parameter-turn-on-sequences” in the refinement strategy
• Make inadequate analytical profile functions redundant
• Stable, fast and accurate fitting even with vague start parameters

Consequently, TOPAS defines the newest generation of pattern analysis software. With a users base of about 3000 it marks the standard for Rietveld analysis.