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Crystal structure refinement of α‐Si 3 N 4 using synchrotron radiation powder diffraction data: unbiased refinement strategy
Author(s) -
Toraya H.
Publication year - 2000
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889899013060
Subject(s) - synchrotron radiation , powder diffraction , diffraction , crystallography , crystal structure , x ray crystallography , rietveld refinement , materials science , crystal (programming language) , analytical chemistry (journal) , chemistry , physics , optics , computer science , programming language , chromatography
The crystal structure of α‐silicon nitride (Si 3 N 4 ) was refined by the Rietveld method using synchrotron radiation powder diffraction data (wavelength = 1.2 Å) collected at station BL‐4B2 in the Photon Factory. A refinement procedure that adopted a new weight function, w = 1/ ( Y o is the observed profile intensity and e ≃ 2), for the least‐squares fitting [Toraya (1998). J. Appl. Cryst . 31 , 333–343] was studied. The most reasonable structural parameters were obtained with e = 1.7. Crystal data of α‐Si 3 N 4 : trigonal, P 31 c , a = 7.75193 (3), c = 5.61949 (4) Å, V = 292.447 (3) Å 3 , Z = 4; R p = 5.08, R wp = 6.50, R B = 3.36, R F = 2.26%. The following five factors are considered equally important for deriving accurate structural parameters from powder diffraction data: (i) sufficiently large sin θ/λ range of >0.8 Å −1 ; (ii) adequate counting statistics; (iii) correct profile model; (iv) proper weighting on observations to give a uniform distribution of the mean weighted squared residuals; (v) high‐angular‐resolution powder diffraction data.