Rietveld refinement of Ba5(AsO4)3Cl from high-resolution synchrotron data

Bell, A.M.T.; Henderson, C.M.B.; Wendlandt, R.F.; Harrison, W.J.

doi:10.1107/S1600536808026901

Volume 64
Part 9
Pages i63-i64
September 2008

Received 30 July 2008
Accepted 20 August 2008
Online 23 August 2008

Key indicators
Powder Synchrotron study
T = 298 K
Mean (As-O) = 0.040 Å
R = 0.059
wR = 0.082
Data-to-parameter ratio = 22.1
Details

Rietveld refinement of Ba₅(AsO₄)₃Cl from high-resolution synchrotron data

Anthony M. T. Bell,^a ^* C. Michael B. Henderson,^b Richard F. Wendlandt ^c and Wendy J. Harrison ^c

^aSynchrotron Radiation Source, STFC Daresbury Laboratory, Daresbury, Warrington, Cheshire, WA4 4AD, England,^bSchool of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, M13 9PL, England, and ^cDepartment of Geology and Geological Engineering, Colorado School of Mines, Golden, CO 80401, USA
Correspondence e-mail: a.m.t.bell@dl.ac.uk

The apatite-type compound Ba₅(AsO₄)₃Cl, pentabarium tris[arsenate(V)] chloride, has been synthesized by ion exchange at high temperature from a synthetic sample of mimetite (Pb₅(AsO₄)₃Cl) with BaCO₃ as a by-product. The results of the Rietveld refinement, based on high resolution synchrotron X-ray powder diffraction data, show that the title compound crystallizes in the same structure as other halogenoapatites with general formula A₅(YO₄)₃X (A = divalent cation, Y = pentavalent cation, X = Cl, Br) in space group P6₃/m. The structure consists of isolated tetrahedral AsO₄^3- anions (m symmetry), separated by two crystallographically independent Ba²⁺ cations that are located on mirror planes and threefold rotation axes, respectively. The Cl^- anions are at the 2b sites ( $[\overline{3}]$ symmetry) and are located in the channels of the structure.

Related literature

For crystal chemistry of apatites, see: Mercier et al. (2005); White & ZhiLi (2003); Wu et al. (2003). For powder diffraction data on Ba-containing As-apatites, see: Kreidler & Hummel (1970); Dunn & Rouse (1978). Atomic coordinates as starting parameters for the Rietveld (Rietveld, 1969) refinement of the present phases were taken from Chengjun et al. (2005); Dai et al. (1991); de Villiers et al. (1971). For related Ba-Cl-apatites, see: Đordevic et al. (2008); Hata et al. (1979); Reinen et al.(1986); Roh & Hong (2005); Schiff-Francois et al. (1979). For synthetic work, see: Baker (1966); Essington (1988); Harrison et al. (2002).

Experimental

Crystal data

As₃Ba₅ClO₁₂
M_r = 1138.85
Hexagonal, P 6₃ /m
a = 10.5570 (1) Å
c = 7.73912 (8) Å
V = 746.98 (1) Å³
Z = 2
Synchrotron radiation
= 0.998043 Å
= 56.07 (1) mm^-1
T = 298 K
Specimen shape: cylinder
40 × 0.7 × 0.7 mm
Specimen prepared at 100 kPa
Specimen prepared at 1258 K
Particle morphology: powder, white

Data collection

In-house design diffractometer
Specimen mounting: capillary
Specimen mounted in transmission mode
Scan method: step
Absorption correction: none
2_min = 2, 2_max = 70°
Increment in 2 = 0.01°

Refinement

R_p = 0.059
R_wp = 0.082
R_exp = 0.067
R_B = 0.090
S = 1.23
Excluded region(s): 2-6 degrees 2.
Profile function: Fundamental Parameters
464 Bragg reflections
21 parameters
Preferred orientation correction: none

Table 1
Selected geometric parameters (Å, °)

Ba1-O1	2.67 (5)
Ba1-O2ⁱ	2.81 (4)
Ba1-O3ⁱ	3.12 (3)
Ba2-O2ⁱⁱ	2.59 (4)
Ba2-O3ⁱⁱⁱ	2.62 (4)
Ba2-O3^iv	3.05 (4)
Ba2-O1^v	3.14 (4)
Ba2-Cl1^iv	3.281 (5)
As1-O3	1.64 (2)
As1-O1	1.70 (8)
As1-O2	1.70 (4)

O3-As1-O3^vi	118 (2)
O3-As1-O1	108 (1)
O3-As1-O2	108 (2)
O1-As1-O2	106 (2)
Symmetry codes: (i) x-y, x, -z; (ii) -y+1, x-y+1, z; (iii) y, -x+y+1, -z; (iv) x, y+1, z; (v) -x+y, -x+1, z; (vi) $[x, y, -z+{\script{1\over 2}}]$ .

Data collection: local software; cell refinement: CELREF (Laugier & Bochu, 2003); data reduction: local software; method used to solve structure: coordinates taken from a related compound; program(s) used to refine structure: TOPAS (Coelho, 2000); molecular graphics: Balls and Sticks (Kang & Ozawa, 2003); software used to prepare material for publication: publCIF (Westrip, 2008).

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: WM2188 ).

Acknowledgements

AMTB acknowledges the use of the EPSRC's Chemical Database Service at Daresbury (Fletcher et al., 1996). AMTB also acknowledges the referees and Co-editor whose suggestions and comments helped to improve this paper.

References

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