Structure refinement with X‐ray powder diffraction data for synthetic calcium hydroxyapatite by Rietveld method

Abstract

Ca,(l'O,),OH, M , = 502.3, hexagoiial, P 6Jti1, a = Y.4207(3), c = 6.8780(2) A, V =-= 528.67 AJ, 2 = 2, D , = 3.156 Mg . iii-', C u K a , IKa, = 1.54051, AKa, = 1.54433 A, p = 26.25 i i i t i i -l , F(OO0) = 500, T = 294 K. T h e powder diffructioii pattern was arialysetl by tho Rietveld tilethod. T h e parameters were refined by t h e progratii P P S R (DBW2.9) to final R-factors R , = 0.079, R,, = 0.081 and R, = 0.015. C~L~( P O~)~O H , M , = 502.3, hex&g~tittl, P 6Jtli, u = Y.4207(3), c = (i.8?80(2) A,, c' = 528.87 AJ, 2 = 2, D , = 3.158 Mg I I I -~, CuKa, AKa, = 1.54051, AKa, = 1.54434 A [L = 26.25 i~i t t i -~, F(000) = 500, T' = 284 K . D a s Pr~lverl~eugutigstliajil.ullll,, w~~r t l t : t i i i t der Rietveld-Methode analysiert. Die Ptlraineter wurden init deli1 Prograiiitil P P S R (DRW2.9) bis zii den abschlielknden R-Faktoren R, = 0.079, R,, = 0.081 uiitl 8 1 , = 0.015 verfeinert.

Rietveld Refinement on X-Ray Diffraction Patterns of Bioapatite in Human Fetal Bones

“…Detailed diffraction studies on single-crystal OHA indicate a monoclinic structure (space group P2 1 /b) (Elliot et al, 1973;Ikoma et al, 1999). However, the hexagonal symmetry works well when dealing with powder diffraction data, and the crystal structure of synthetic OHA is usually described in space group P6 3 /m with a hexagonal unit cell (Posner and Diorio, 1958;Kay et al, 1964;Sudarsanan and Young, 1969;Pritzkow and Rentsch, 1985). The crystallographic structure reported by Sudarsanan and Young (1969) was adopted as a structural model in the Rietveld refinement of synthetic OHA and bone bioapatite samples.…”

Initial Rietveld characterisation of biological calcifications

“…Atomic fractional coordinates and occupancies were refined only after convergence had been achieved (or five cycles had been performed) with refinement of background, lattice, and microstructural parameters. Atomic thermal parameters were not refined but constrained to values previously supplied from a Rietveld refinement of stoichiometric HAP (Pritzkow & Rentsch, 1985). An implication of this strategy is discussed later.…”

“…It tends to provide better convergence with fewer fitting parameters [the Caglioti coefficients (Caglioti, et al 1958) are not refined]. The starting structural model was that of stoichiometric HAP (Pritzkow & Rentsch, 1985) and variables were introduced sequentially during the refinement process. As recommended by the authors of LS1, the size and microstrain tensors were restricted to the crystal symmetry and the background was modeled with a four term polynomial.…”