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High-resolution synchrotron powder diffraction measurements were carried out at the 32-ID beamline of the Advanced Photon Source of Argonne National Laboratory in order to clarify the structure of geological aragonite, a widely abundant polymorph of CaCO3. The investigated crystals were practically free of impurity atoms, as measured by wavelength-dispersive X-ray spectroscopy in scanning electron microscopy. A superior quality of diffraction data was achieved by using the 11-channel 111 Si multi-analyzer of the diffracted beam. Applying the Rietveld refinement procedure to the high-resolution diffraction spectra, we were able to extract the aragonite lattice parameters with an accuracy of about 20 p.p.m. The data obtained unambiguously confirm that pure aragonite crystals have orthorhombic symmetry.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768105005240/lc5015sup1.cif
Contains datablocks PMCN_SF43P_publ, PMCN_SF43P_phase_1, PMCN_SF43P_phase_2, PMCN_SF43P_phase_3, PMCN_SF43P_overall

txt

Text file https://doi.org/10.1107/S0108768105005240/lc5015sup2.txt
Powder data

Computing details top

Figures top
[Figure 1] Fig. 1.  
(PMCN_SF43P_phase_1) top
Crystal data top
CCaO3c = 5.742852 (15) Å
Mr = 100.09V = 227.08 (1) Å3
Orthorhombic, PmcnZ = 4
a = 4.961830 (13) Å? radiation, λ = 0.49581 Å
b = 7.96914 (2) Å?, ? × ? × ? mm
Data collection top
Radiation source: synchrotron, APS beamline 32-ID
Refinement top
Least-squares matrix: full? data points
Rp = ?78 parameters
Rwp = ?0 restraints
Rexp = ?(Δ/σ)max = 0.04
χ2 = 6.864
Crystal data top
CCaO3c = 5.742852 (15) Å
Mr = 100.09V = 227.08 (1) Å3
Orthorhombic, PmcnZ = 4
a = 4.961830 (13) Å? radiation, λ = 0.49581 Å
b = 7.96914 (2) Å?, ? × ? × ? mm
Data collection top
Refinement top
Rp = ?? data points
Rwp = ?78 parameters
Rexp = ?0 restraints
χ2 = 6.864
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Ca0.250.41502 (2)0.75985 (4)0.00764
C0.250.76194 (12)0.08240 (14)0.01523
O10.250.92238 (8)0.09453 (8)0.01161
O20.47499 (7)0.68012 (5)0.08725 (7)0.01035
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ca0.00450 (9)0.00677 (9)0.01166 (10)0.00.00.00195 (14)
C0.0198 (6)0.0210 (6)0.0049 (5)0.00.00.0005 (5)
O10.0127 (4)0.0033 (3)0.0188 (4)0.00.00.0037 (3)
O20.0004 (2)0.0107 (2)0.0200 (3)0.00669 (18)0.0003 (2)0.0016 (2)
(PMCN_SF43P_phase_2) top
Crystal data top
O2SiV = 113.06 (1) Å3
Mr = 60.08Z = 3
Trigonal, P3221? radiation, λ = 0.49581 Å
a = 4.91427 (12) Å?, ? × ? × ? mm
c = 5.4058 (2) Å
Data collection top
Radiation source: synchrotron, APS beamline 32-ID
Refinement top
Least-squares matrix: full? data points
Rp = ?78 parameters
Rwp = ?0 restraints
Rexp = ?(Δ/σ)max = 0.04
χ2 = 6.864
Crystal data top
O2SiV = 113.06 (1) Å3
Mr = 60.08Z = 3
Trigonal, P3221? radiation, λ = 0.49581 Å
a = 4.91427 (12) Å?, ? × ? × ? mm
c = 5.4058 (2) Å
Data collection top
Refinement top
Rp = ?? data points
Rwp = ?78 parameters
Rexp = ?0 restraints
χ2 = 6.864
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Si10.47230.00.666670.00754
O10.4160.26580.78810.01747
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Si10.00750.00950.00630.004750.0020.004
O10.0260.020.01240.0160.0030.005
(PMCN_SF43P_phase_3) top
Crystal data top
CCaO3V = 367.41 (4) Å3
Mr = 100.09Z = 6
Trigonal, R3c? radiation, λ = 0.49581 Å
a = 4.9870 (6) Å?, ? × ? × ? mm
c = 17.058 (2) Å
Data collection top
Radiation source: synchrotron, APS beamline 32-ID
Refinement top
Least-squares matrix: full? data points
Rp = ?78 parameters
Rwp = ?0 restraints
Rexp = ?(Δ/σ)max = 0.04
χ2 = 6.864
Crystal data top
CCaO3V = 367.41 (4) Å3
Mr = 100.09Z = 6
Trigonal, R3c? radiation, λ = 0.49581 Å
a = 4.9870 (6) Å?, ? × ? × ? mm
c = 17.058 (2) Å
Data collection top
Refinement top
Rp = ?? data points
Rwp = ?78 parameters
Rexp = ?0 restraints
χ2 = 6.864
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Ca10.00.00.00.01057
C10.00.00.250.00997
O10.2465 (7)0.00.250.01767
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ca10.01080.01080.01010.00540.00.0
C10.00940.00940.01110.00470.00.0
O10.01230.02340.0210.01170.00390.0078

Experimental details

(PMCN_SF43P_phase_1)(PMCN_SF43P_phase_2)(PMCN_SF43P_phase_3)
Crystal data
Chemical formulaCCaO3O2SiCCaO3
Mr100.0960.08100.09
Crystal system, space groupOrthorhombic, PmcnTrigonal, P3221Trigonal, R3c
Temperature (K)???
a, b, c (Å)4.961830 (13), 7.96914 (2), 5.742852 (15)4.91427 (12), 4.91427, 5.4058 (2)4.9870 (6), 4.987, 17.058 (2)
α, β, γ (°)90, 90, 9090, 90, 12090, 90, 120
V3)227.08 (1)113.06 (1)367.41 (4)
Z436
Radiation type?, λ = 0.49581 Å?, λ = 0.49581 Å?, λ = 0.49581 Å
Specimen shape, size (mm)?, ? × ? × ??, ? × ? × ??, ? × ? × ?
Data collection
Diffractometer???
Specimen mounting???
Data collection mode???
Scan method???
2θ values (°)2θmin = ? 2θmax = ? 2θstep = ?2θmin = ? 2θmax = ? 2θstep = ?2θmin = ? 2θmax = ? 2θstep = ?
Refinement
R factors and goodness of fitRp = ?, Rwp = ?, Rexp = ?, χ2 = 6.864Rp = ?, Rwp = ?, Rexp = ?, χ2 = 6.864Rp = ?, Rwp = ?, Rexp = ?, χ2 = 6.864
No. of data points???
No. of parameters787878

Computer programs: GSAS.

 

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