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
Crystal data top
CCaO3 | c = 5.742852 (15) Å |
Mr = 100.09 | V = 227.08 (1) Å3 |
Orthorhombic, Pmcn | Z = 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
CCaO3 | c = 5.742852 (15) Å |
Mr = 100.09 | V = 227.08 (1) Å3 |
Orthorhombic, Pmcn | Z = 4 |
a = 4.961830 (13) Å | ? radiation, λ = 0.49581 Å |
b = 7.96914 (2) Å | ?, ? × ? × ? mm |
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 | x | y | z | Uiso*/Ueq | |
Ca | 0.25 | 0.41502 (2) | 0.75985 (4) | 0.00764 | |
C | 0.25 | 0.76194 (12) | −0.08240 (14) | 0.01523 | |
O1 | 0.25 | 0.92238 (8) | −0.09453 (8) | 0.01161 | |
O2 | 0.47499 (7) | 0.68012 (5) | −0.08725 (7) | 0.01035 | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Ca | 0.00450 (9) | 0.00677 (9) | 0.01166 (10) | 0.0 | 0.0 | −0.00195 (14) |
C | 0.0198 (6) | 0.0210 (6) | 0.0049 (5) | 0.0 | 0.0 | −0.0005 (5) |
O1 | 0.0127 (4) | 0.0033 (3) | 0.0188 (4) | 0.0 | 0.0 | 0.0037 (3) |
O2 | 0.0004 (2) | 0.0107 (2) | 0.0200 (3) | 0.00669 (18) | 0.0003 (2) | 0.0016 (2) |
Crystal data top
O2Si | V = 113.06 (1) Å3 |
Mr = 60.08 | Z = 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
O2Si | V = 113.06 (1) Å3 |
Mr = 60.08 | Z = 3 |
Trigonal, P3221 | ? radiation, λ = 0.49581 Å |
a = 4.91427 (12) Å | ?, ? × ? × ? mm |
c = 5.4058 (2) Å | |
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 | x | y | z | Uiso*/Ueq | |
Si1 | 0.4723 | 0.0 | 0.66667 | 0.00754 | |
O1 | 0.416 | 0.2658 | 0.7881 | 0.01747 | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Si1 | 0.0075 | 0.0095 | 0.0063 | 0.00475 | −0.002 | −0.004 |
O1 | 0.026 | 0.02 | 0.0124 | 0.016 | −0.003 | −0.005 |
Crystal data top
CCaO3 | V = 367.41 (4) Å3 |
Mr = 100.09 | Z = 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
CCaO3 | V = 367.41 (4) Å3 |
Mr = 100.09 | Z = 6 |
Trigonal, R3c | ? radiation, λ = 0.49581 Å |
a = 4.9870 (6) Å | ?, ? × ? × ? mm |
c = 17.058 (2) Å | |
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 | x | y | z | Uiso*/Ueq | |
Ca1 | 0.0 | 0.0 | 0.0 | 0.01057 | |
C1 | 0.0 | 0.0 | 0.25 | 0.00997 | |
O1 | 0.2465 (7) | 0.0 | 0.25 | 0.01767 | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Ca1 | 0.0108 | 0.0108 | 0.0101 | 0.0054 | 0.0 | 0.0 |
C1 | 0.0094 | 0.0094 | 0.0111 | 0.0047 | 0.0 | 0.0 |
O1 | 0.0123 | 0.0234 | 0.021 | 0.0117 | −0.0039 | −0.0078 |
Experimental details
| (PMCN_SF43P_phase_1) | (PMCN_SF43P_phase_2) | (PMCN_SF43P_phase_3) |
Crystal data |
Chemical formula | CCaO3 | O2Si | CCaO3 |
Mr | 100.09 | 60.08 | 100.09 |
Crystal system, space group | Orthorhombic, Pmcn | Trigonal, P3221 | Trigonal, 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, 90 | 90, 90, 120 | 90, 90, 120 |
V (Å3) | 227.08 (1) | 113.06 (1) | 367.41 (4) |
Z | 4 | 3 | 6 |
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 fit | Rp = ?, Rwp = ?, Rexp = ?, χ2 = 6.864 | Rp = ?, Rwp = ?, Rexp = ?, χ2 = 6.864 | Rp = ?, Rwp = ?, Rexp = ?, χ2 = 6.864 |
No. of data points | ? | ? | ? |
No. of parameters | 78 | 78 | 78 |