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Structure of K2TaF7 at 720oC - a combined use of synchrotron powder data and solid state DFT calculation

Ľubomír Smrčok 1Michela Brunelli 2Miroslav Boča 1Marian Kucharík 1

1. Institute Of Inorganic Chemistry, Slovak Academy of Sciences (IIC), Dubravska cesta 9, Bratislava SK-84536, Slovakia (Slovak Rep.)
2. Europen Synchrotron Radiation Facility (ESRF), 6, Jules Horowitz, Grenoble 38000, France

The structure of the title compound was optimized by energy minimization in solid state using a plane waves DFT computation where the lattice parameters were obtained by LeBail method from the synchrotron X-ray powder diffraction data collected at 720oC.  Owing to sample corrosiveness it had to be filled in a thin-walled Pt capillary. It was found that the structure corresponds to that of  beta-K2TaF7 phase. It was also shown that solid state DFT methods could be an accurate alternative to Rietveld refinement, providing a remedy to the chronic pain of standard powder refinements - lack of information extractable from a powder pattern. The size of the problems tractable by the current solid state DFT methods running on a laboratory computer nowadays reaches 500-1000 atoms/unit cell, i.e. well exceeds widely accepted limits for unrestrained powder refinements, which frequently fail in providing accurate results even for the structures built of much smaller numbers of atoms. 

Ľ.Smrčok, M.Brunelli, M.Boča and M.Kucharík J.Appl. Cryst. (2008) 41(3). In press.


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Presentation: Poster at 11th European Powder Diffraction Conference, Poster session, by Ľubomír Smrčok
See On-line Journal of 11th European Powder Diffraction Conference

Submitted: 2008-05-08 10:32
Revised:   2009-06-07 00:48