Download citation
Download citation
link to html
The incommensurate structure of (Sr0.13Ca0.87)2CoSi2O7 at room temperature has been determined from single-crystal X-­ray diffraction data. The compound has a non-centrosymmetric tetragonal basic cell of a = 7.8743 (4) and c = 5.0417 (2) Å with the space group P421m. The refinements of the basic structure converged to R = 0.038 for 757 main reflections. The two-dimensional incommensurate structure is characterized by the wavevectors q1 = 0.286 (3)(a* + b*) and q2 = 0.286 (3)(-a* + b*), where a*, b* are the reciprocal lattice vectors of the basic structure. With the (3 + 2)-dimensional superspace group Pp4mgP421m, the refinements converged to R = 0.071 for 1697 observed reflections (757 main and 940 satellite reflections). The structure is described in terms of displacement of the atoms, rotation, distortion of CoO4 and SiO4 tetrahedra, and the partial ordering of the Sr and Ca atoms accompanied with the modulation. Correlated evolution of these features throughout the crystal gives rise to various oxygen coordination around Ca/Sr. Comparison of the derived modulated structure to that of Ca2CoSi2O7 clarified that the partial substitution of Ca by large alkaline-earth atoms such as Sr should decrease the distortion of the polyhedra around the cations.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768100006716/sn0002sup1.cif
Contains datablocks default, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108768100006716/sn0002sup2.hkl
Supplementary material

Computing details top

Figures top
[Figure 1]
[Figure 2]
[Figure 3]
[Figure 4]
[Figure 5]
[Figure 6]
[Figure 7]
[Figure 8]
[Figure 9]
[Figure 10]
[Figure 11]
(I) top
Crystal data top
(Sr0.13Ca0.87)2CoSi2O7V = 312.61 (3) Å3
Mr = 319.6Z = 2
Tetragonal, P421mF(000) = 311
q1 = 0.28600a* + 0.28600b*; q2 = -0.28600a* + 0.28600b*Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P -4 2abµ = 6.74 mm1
a = 7.8743 (4) Å, blue
c = 5.0417 (2) Å0.15 mm (radius)
Data collection top
CAD4
diffractometer
θmax = 50.0°, θmin = 1.5°
ω/2θ scansh = ??
Absorption correction: analytical
?
k = ??
Tmin = 0.225, Tmax = 0.273l = ??
8207 independent reflections2 standard reflections
1697 reflections with 2.5 intensity decay: 1.3, 1.5%
Refinement top
Refinement on F
R[F2 > 2σ(F2)] = 0.070Δρmax = 2.59 e Å3
wR(F2) = 0.052Δρmin = 2.94 e Å3
1697 reflectionsExtinction correction: B-C type 1 Lorentzian isotropic
107 parametersExtinction coefficient: 0.102492
Unit
Crystal data top
(Sr0.13Ca0.87)2CoSi2O7V = 312.61 (3) Å3
Mr = 319.6Z = 2
Tetragonal, P421mMo Kα radiation
q1 = 0.28600a* + 0.28600b*; q2 = -0.28600a* + 0.28600b*µ = 6.74 mm1
a = 7.8743 (4) Å0.15 mm (radius)
c = 5.0417 (2) Å
Data collection top
CAD4
diffractometer
1697 reflections with 2.5
Absorption correction: analytical
?
2 standard reflections
Tmin = 0.225, Tmax = 0.273 intensity decay: 1.3, 1.5%
8207 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.070107 parameters
wR(F2) = 0.052Δρmax = 2.59 e Å3
1697 reflectionsΔρmin = 2.94 e Å3
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Sr0.332340.167660.50580.016450.128
Ca0.33234 (4)0.16766 (4)0.5058 (1)0.01845 (8)0.872 (3)
Co0000.01184 (7)
Si0.13915 (7)0.36085 (7)0.9382 (1)0.0113 (1)
O100.50.8254 (6)0.0354 (8)
O20.1401 (2)0.3599 (2)0.2547 (4)0.0244 (4)
O30.0798 (3)0.1894 (2)0.7863 (3)0.0289 (5)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Sr0.0199 (2)0.0199 (2)0.0100 (2)0.0089 (2)0.0015 (1)0.0015 (1)
Ca0.0199 (2)0.0199 (2)0.0100 (2)0.0089 (2)0.0015 (1)0.0015 (1)
Co0.0109 (1)0.0109 (1)0.0109 (1)000
Si0.0112 (2)0.0112 (2)0.0076 (2)0.0014 (2)0.0000 (1)0.0000 (1)
O10.0450 (16)0.0450 (16)0.0070 (9)0.0330 (16)00
O20.0303 (8)0.0303 (8)0.0073 (7)0.0140 (10)0.0017 (5)0.0017 (5)
O30.0420 (10)0.0155 (6)0.0141 (8)0.0120 (7)0.0064 (8)0.0014 (6)

Experimental details

Crystal data
Chemical formula(Sr0.13Ca0.87)2CoSi2O7
Mr319.6
Crystal system, space groupTetragonal, P421m
Temperature (K)?
Wave vectorsq1 = 0.28600a* + 0.28600b*; q2 = -0.28600a* + 0.28600b*
a, c (Å)7.8743 (4), 5.0417 (2)
V3)312.61 (3)
Z2
Radiation typeMo Kα
µ (mm1)6.74
Crystal size (mm)0.15 (radius)
Data collection
DiffractometerCAD4
diffractometer
Absorption correctionAnalytical
Tmin, Tmax0.225, 0.273
No. of measured, independent and
observed (2.5) reflections
?, 8207, 1697
Rint?
(sin θ/λ)max1)1.078
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.070, 0.052, ?
No. of reflections1697
No. of parameters107
No. of restraints?
Δρmax, Δρmin (e Å3)2.59, 2.94

 

Follow Acta Cryst. B
Sign up for e-alerts
Follow Acta Cryst. on Twitter
Follow us on facebook
Sign up for RSS feeds