Reinvestigation of the crystal structure of Ca₂Ce₈(SiO₄)₆O₂ apatite by Rietveld refinement

The lattice parameters of apatite-type Ca₂Ca₈(SiO₄)₆O₂ determined from X-ray powder diffraction data are inconsistent with those found in the literature for the same type of material. Hence the structure was redetermined and compared with previously published data.

Key indicators

• Powder X-ray study
• T = 293 K
• Mean [sigma](Si-O) = 0.011 Å
• Disorder in main residue
• R factor = 0.044
• wR factor = 0.000
• Data-to-parameter ratio = 0.0

checkCIF/PLATON results

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Datablock: I


Alert level G
PLAT004_ALERT_5_G Polymeric Structure Found with Maximum Dimension          3 Info
PLAT045_ALERT_1_G Calculated and Reported Z Differ by a Factor ...       2.00 Check
PLAT143_ALERT_4_G s.u. on c - Axis Small or Missing ..............    0.00006 Ang.
PLAT152_ALERT_1_G The Supplied and Calc. Volume s.u. Differ by ...          3 Units
PLAT300_ALERT_4_G Atom Site Occupancy of Ce_A       Constrained at        0.5 Check
PLAT300_ALERT_4_G Atom Site Occupancy of Ca_A       Constrained at        0.5 Check
PLAT301_ALERT_3_G Main Residue  Disorder ..............(Resd  1  )         8% Note
PLAT720_ALERT_4_G Number of Unusual/Non-Standard Labels ..........          8 Note
PLAT794_ALERT_5_G Tentative Bond Valency for Ce_B      (III)     .       2.84 Info

   0 ALERT level A = Most likely a serious problem - resolve or explain
   0 ALERT level B = A potentially serious problem, consider carefully
   0 ALERT level C = Check. Ensure it is not caused by an omission or oversight
   9 ALERT level G = General information/check it is not something unexpected

   2 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   0 ALERT type 2 Indicator that the structure model may be wrong or deficient
   1 ALERT type 3 Indicator that the structure quality may be low
   4 ALERT type 4 Improvement, methodology, query or suggestion
   2 ALERT type 5 Informative message, check

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Computing details

Data collection: Data Collector (Panalytical, 2011); cell refinement: JANA2006 (Petříček et al., 2014); data reduction: JANA2006 (Petříček et al., 2014); program(s) used to solve structure: JANA2006 (Petříček et al., 2014); program(s) used to refine structure: JANA2006 (Petříček et al., 2014); molecular graphics: VESTA (Momma & Izumi, 2011); software used to prepare material for publication: publCIF (Westrip, 2010).

Dicalcium octacerium hexakis(silicate) dioxide

Crystal data

Ca2Ce8(SiO4)6O2	y
Mr = 1785.6	Dx = 5.239 Mg m^−3
Hexagonal, P63/m	Cu Kα1 radiation, λ = 1.540562, 1.544390 Å
a = 9.59912 (6) Å	T = 293 K
c = 7.09284 (6) Å	Particle morphology: plate-like
V = 566.00 (1) Å^3	brown
Z = 1	flat_sheet, 25 × 25 mm
F(000) = 796	Specimen preparation: Prepared at 1873 K and 100 kPa, cooled at 30 K min^−1

Data collection

Panalytical XPert MPD Pro diffractometer	Data collection mode: reflection
Radiation source: sealed X-ray tube	Scan method: step
Specimen mounting: packed powder pellet	2θmin = 10.023°, 2θmax = 130.010°, 2θstep = 0.017°

Refinement

Rp = 0.045	28 parameters
Rwp = 0.059	0 restraints
Rexp = 0.034	9 constraints
R(F) = 0.046	Weighting scheme based on measured s.u.'s
6881 data points	(Δ/σ)max = 0.005
Profile function: pseudo-Voigt	Background function: Legendre polynoms

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Ca_a	0.333333	0.666667	−0.0009 (7)	0.008*	0.5
Ce_a	0.333333	0.666667	−0.0009 (7)	0.008*	0.5
Ce_b	0.23194 (13)	−0.01214 (18)	0.25	0.006*
Si_c	0.4040 (6)	0.3713 (6)	0.25	0.005*
O1_c	0.3293 (13)	0.4865 (12)	0.25	0.003*
O2_c	0.5980 (14)	0.4634 (13)	0.25	0.003*
O3_c	0.3410 (7)	0.2594 (8)	0.0668 (9)	0.003*
O4_d	0	0	0.25	0.003*

Geometric parameters (Å, º)

Ca_a—Ca_a^i	3.534 (7)	Ce_a—O1_c	2.468 (10)
Ca_a—Ca_a^ii	3.559 (7)	Ce_a—O1_c^vi	2.468 (8)
Ca_a—Ce_a	0	Ce_a—O1_c^vii	2.468 (13)
Ca_a—Ce_a^i	3.534 (7)	Ce_a—O2_c^iii	2.437 (11)
Ca_a—Ce_a^ii	3.559 (7)	Ce_a—O2_c^iv	2.437 (10)
Ca_a—Si_c^iii	3.246 (6)	Ce_a—O2_c^v	2.437 (13)
Ca_a—Si_c^iv	3.246 (8)	Ce_b—O3_c^viii	2.396 (7)
Ca_a—Si_c^v	3.246 (5)	Ce_b—O3_c^ix	2.396 (7)
Ca_a—O2_c^iii	2.437 (11)	Ce_b—O4_d	2.2870 (15)
Ca_a—O2_c^iv	2.437 (10)	Si_c—O1_c	1.590 (16)
Ca_a—O2_c^v	2.437 (13)	Si_c—O2_c	1.614 (13)
Ce_a—Ce_a^i	3.534 (7)	Si_c—O3_c	1.600 (7)
Ce_a—Ce_a^ii	3.559 (7)	Si_c—O3_c^ii	1.600 (7)
Ca_a^i—Ca_a—Ca_a^ii	180.0 (5)	Ca_a^i—Ce_a—O2_c^v	43.5 (3)
Ca_a^i—Ca_a—Ce_a	0	Ca_a^ii—Ce_a—Ce_a^i	180.0 (5)
Ca_a^i—Ca_a—Ce_a^i	0.0 (5)	Ca_a^ii—Ce_a—Ce_a^ii	0.0 (5)
Ca_a^i—Ca_a—Ce_a^ii	180.0 (5)	Ca_a^ii—Ce_a—O1_c	43.9 (2)
Ca_a^i—Ca_a—Si_c^iii	57.01 (10)	Ca_a^ii—Ce_a—O1_c^vi	43.87 (19)
Ca_a^i—Ca_a—Si_c^iv	57.01 (11)	Ca_a^ii—Ce_a—O1_c^vii	43.9 (3)
Ca_a^i—Ca_a—Si_c^v	57.01 (9)	Ca_a^ii—Ce_a—O2_c^iii	136.5 (3)
Ca_a^i—Ca_a—O2_c^iii	43.5 (3)	Ca_a^ii—Ce_a—O2_c^iv	136.5 (3)
Ca_a^i—Ca_a—O2_c^iv	43.5 (3)	Ca_a^ii—Ce_a—O2_c^v	136.5 (3)
Ca_a^i—Ca_a—O2_c^v	43.5 (3)	Ce_a^i—Ce_a—Ce_a^ii	180.0 (5)
Ca_a^ii—Ca_a—Ce_a	0	Ce_a^i—Ce_a—O1_c	136.1 (2)
Ca_a^ii—Ca_a—Ce_a^i	180.0 (5)	Ce_a^i—Ce_a—O1_c^vi	136.13 (19)
Ca_a^ii—Ca_a—Ce_a^ii	0.0 (5)	Ce_a^i—Ce_a—O1_c^vii	136.1 (3)
Ca_a^ii—Ca_a—Si_c^iii	122.99 (10)	Ce_a^i—Ce_a—O2_c^iii	43.5 (3)
Ca_a^ii—Ca_a—Si_c^iv	122.99 (11)	Ce_a^i—Ce_a—O2_c^iv	43.5 (3)
Ca_a^ii—Ca_a—Si_c^v	122.99 (9)	Ce_a^i—Ce_a—O2_c^v	43.5 (3)
Ca_a^ii—Ca_a—O2_c^iii	136.5 (3)	Ce_a^ii—Ce_a—O1_c	43.9 (2)
Ca_a^ii—Ca_a—O2_c^iv	136.5 (3)	Ce_a^ii—Ce_a—O1_c^vi	43.87 (19)
Ca_a^ii—Ca_a—O2_c^v	136.5 (3)	Ce_a^ii—Ce_a—O1_c^vii	43.9 (3)
Ce_a—Ca_a—Ce_a^i	0	Ce_a^ii—Ce_a—O2_c^iii	136.5 (3)
Ce_a—Ca_a—Ce_a^ii	0	Ce_a^ii—Ce_a—O2_c^iv	136.5 (3)
Ce_a—Ca_a—Si_c^iii	0	Ce_a^ii—Ce_a—O2_c^v	136.5 (3)
Ce_a—Ca_a—Si_c^iv	0	O1_c—Ce_a—O1_c^vi	73.8 (4)
Ce_a—Ca_a—Si_c^v	0	O1_c—Ce_a—O1_c^vii	73.8 (4)
Ce_a—Ca_a—O2_c^iii	0	O1_c—Ce_a—O2_c^iii	94.4 (3)
Ce_a—Ca_a—O2_c^iv	0	O1_c—Ce_a—O2_c^iv	153.3 (4)
Ce_a—Ca_a—O2_c^v	0	O1_c—Ce_a—O2_c^v	126.7 (3)
Ce_a^i—Ca_a—Ce_a^ii	180.0 (5)	O1_c^vi—Ce_a—O1_c^vii	73.8 (4)
Ce_a^i—Ca_a—Si_c^iii	57.01 (10)	O1_c^vi—Ce_a—O2_c^iii	126.7 (4)
Ce_a^i—Ca_a—Si_c^iv	57.01 (11)	O1_c^vi—Ce_a—O2_c^iv	94.4 (3)
Ce_a^i—Ca_a—Si_c^v	57.01 (9)	O1_c^vi—Ce_a—O2_c^v	153.3 (6)
Ce_a^i—Ca_a—O2_c^iii	43.5 (3)	O1_c^vii—Ce_a—O2_c^iii	153.3 (3)
Ce_a^i—Ca_a—O2_c^iv	43.5 (3)	O1_c^vii—Ce_a—O2_c^iv	126.7 (5)
Ce_a^i—Ca_a—O2_c^v	43.5 (3)	O1_c^vii—Ce_a—O2_c^v	94.4 (4)
Ce_a^ii—Ca_a—Si_c^iii	122.99 (10)	O2_c^iii—Ce_a—O2_c^iv	73.2 (5)
Ce_a^ii—Ca_a—Si_c^iv	122.99 (11)	O2_c^iii—Ce_a—O2_c^v	73.2 (5)
Ce_a^ii—Ca_a—Si_c^v	122.99 (9)	O2_c^iv—Ce_a—O2_c^v	73.2 (3)
Ce_a^ii—Ca_a—O2_c^iii	136.5 (3)	O3_c^viii—Ce_b—O3_c^ix	139.4 (4)
Ce_a^ii—Ca_a—O2_c^iv	136.5 (3)	O3_c^viii—Ce_b—O4_d	105.0 (2)
Ce_a^ii—Ca_a—O2_c^v	136.5 (3)	O3_c^ix—Ce_b—O4_d	105.0 (2)
Si_c^iii—Ca_a—Si_c^iv	93.17 (18)	Ca_a^x—Si_c—Ca_a^xi	65.98 (17)
Si_c^iii—Ca_a—Si_c^v	93.17 (18)	Ca_a^x—Si_c—O1_c	136.4 (2)
Si_c^iii—Ca_a—O2_c^iii	28.7 (3)	Ca_a^x—Si_c—O2_c	46.6 (4)
Si_c^iii—Ca_a—O2_c^iv	64.6 (4)	Ca_a^x—Si_c—O3_c	114.9 (5)
Si_c^iii—Ca_a—O2_c^v	97.0 (4)	Ca_a^x—Si_c—O3_c^ii	62.4 (3)
Si_c^iv—Ca_a—Si_c^v	93.17 (16)	Ca_a^xi—Si_c—O1_c	136.4 (2)
Si_c^iv—Ca_a—O2_c^iii	97.0 (3)	Ca_a^xi—Si_c—O2_c	46.6 (4)
Si_c^iv—Ca_a—O2_c^iv	28.7 (4)	Ca_a^xi—Si_c—O3_c	62.4 (3)
Si_c^iv—Ca_a—O2_c^v	64.6 (3)	Ca_a^xi—Si_c—O3_c^ii	114.9 (5)
Si_c^v—Ca_a—O2_c^iii	64.6 (3)	O1_c—Si_c—O2_c	114.7 (7)
Si_c^v—Ca_a—O2_c^iv	97.0 (2)	O1_c—Si_c—O3_c	108.5 (5)
Si_c^v—Ca_a—O2_c^v	28.7 (3)	O1_c—Si_c—O3_c^ii	108.5 (5)
O2_c^iii—Ca_a—O2_c^iv	73.2 (5)	O2_c—Si_c—O3_c	108.2 (5)
O2_c^iii—Ca_a—O2_c^v	73.2 (5)	O2_c—Si_c—O3_c^ii	108.2 (5)
O2_c^iv—Ca_a—O2_c^v	73.2 (3)	O3_c—Si_c—O3_c^ii	108.6 (4)
Ca_a—Ce_a—Ca_a^i	0	Ce_a—O1_c—Ce_a^ii	92.3 (5)
Ca_a—Ce_a—Ca_a^ii	0	Ce_a—O1_c—Si_c	129.2 (3)
Ca_a—Ce_a—Ce_a^i	0	Ce_a^ii—O1_c—Si_c	129.2 (3)
Ca_a—Ce_a—Ce_a^ii	0	Ca_a^x—O2_c—Ca_a^xi	93.0 (5)
Ca_a—Ce_a—O1_c	0	Ca_a^x—O2_c—Ce_a^x	0.0 (5)
Ca_a—Ce_a—O1_c^vi	0	Ca_a^x—O2_c—Ce_a^xi	93.0 (5)
Ca_a—Ce_a—O1_c^vii	0	Ca_a^x—O2_c—Si_c	104.7 (4)
Ca_a—Ce_a—O2_c^iii	0	Ca_a^xi—O2_c—Ce_a^x	93.0 (5)
Ca_a—Ce_a—O2_c^iv	0	Ca_a^xi—O2_c—Ce_a^xi	0.0 (5)
Ca_a—Ce_a—O2_c^v	0	Ca_a^xi—O2_c—Si_c	104.7 (4)
Ca_a^i—Ce_a—Ca_a^ii	180.0 (5)	Ce_a^x—O2_c—Ce_a^xi	93.0 (5)
Ca_a^i—Ce_a—Ce_a^i	0.0 (5)	Ce_a^x—O2_c—Si_c	104.7 (4)
Ca_a^i—Ce_a—Ce_a^ii	180.0 (5)	Ce_a^xi—O2_c—Si_c	104.7 (4)
Ca_a^i—Ce_a—O1_c	136.1 (2)	Ce_b^v—O3_c—Si_c	146.2 (5)
Ca_a^i—Ce_a—O1_c^vi	136.13 (19)	Ce_b—O4_d—Ce_b^xii	120.00 (5)
Ca_a^i—Ce_a—O1_c^vii	136.1 (3)	Ce_b—O4_d—Ce_b^xiii	120.00 (6)
Ca_a^i—Ce_a—O2_c^iii	43.5 (3)	Ce_b^xii—O4_d—Ce_b^xiii	120.00 (6)
Ca_a^i—Ce_a—O2_c^iv	43.5 (3)

Symmetry codes: (i) x, y, −z−1/2; (ii) x, y, −z+1/2; (iii) −x+1, −y+1, z−1/2; (iv) y, −x+y+1, z−1/2; (v) x−y, x, z−1/2; (vi) −y+1, x−y+1, z; (vii) −x+y, −x+1, z; (viii) y, −x+y, z+1/2; (ix) y, −x+y, −z; (x) −x+1, −y+1, z+1/2; (xi) −x+1, −y+1, −z; (xii) −y, x−y, z; (xiii) −x+y, −x, z.