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A new phase of dicalcium silicate (Ca2SiO4) was formed by heating α-dicalcium silicate hydrate [α-Ca2(SiO4H)OH = α-C2SH] at temperatures of ∼663–763 K, and it was transformed into \alpha _{\rm L} ^\prime-Ca2SiO4 (= \alpha _{\rm L} ^\prime-C2S) above ∼1193 K. The crystal structure of the new phase (hereafter called x-C2S) has been determined by simulated annealing and refined by the Rietveld method using synchrotron radiation powder diffraction data. The structure consists of isolated SiO4 tetrahedra and a three-dimensional CaOn polyhedral network, forming a new structural type of dicalcium silicate. A structural change from α-C2SH to x-C2S is compelled by large displacements of SiO4 tetrahedra, accompanied by dehydration, in the direction perpendicular to the two-dimensional Ca(O,OH)n polyhedral network in α-C2SH. With increasing temperature, sizes of CaOn polyhedra in x-C2S become too large to confine Ca atoms at the sixfold to eightfold coordination sites. Then the structure of x-C2S is transformed into \alpha _{\rm L} ^\prime-C2S, having eightfold to tenfold coordination sites for the Ca atoms.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768102005189/ck0012sup1.cif
Contains datablock CK0012

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0108768102005189/ck0012sup2.rtv
Contains datablock ck0012

Computing details top

Cell refinement: WPPF(ver.3.00); data reduction: DATAPRO(ver.2.00); program(s) used to solve structure: DSS(ver.1.00); program(s) used to refine structure: PFLS(ver.5.00); molecular graphics: Ball&Stick.

Figures top
[Figure 1]
[Figure 2]
[Figure 3]
[Figure 4]
[Figure 5]
dicalcium silicate top
Crystal data top
Ca2SiO4Z = 8
Mr = 172.24F(000) = 688
Monoclinic, P21/cDx = 2.91 Mg m3
a = 8.2127 (5) ÅSynchrotron radiation, λ = 1.598 Å
b = 9.7930 (4) ÅT = 298 K
c = 9.7954 (5) ÅParticle morphology: plate-like
β = 94.848 (5)°white
V = 785.00 (7) Å3flat sheet, 29 × 29 mm
Data collection top
MDS, 2-axis, multiple-detector system
diffractometer
Data collection mode: reflection
Radiation source: synchrotron radiationScan method: step
Double-crystal Si(111) monochromator2θmin = 10°, 2θmax = 155°, 2θstep = 0.005°
Specimen mounting: Sample was mounted on a glass specimen holder.
Refinement top
Rp = 0.084Excluded region(s): none
Rwp = 0.116Profile function: pseudo-Voigt
Rexp = 0.0511/(Yi)
RBragg = 0.070
χ2 = 5.198Background function: polynomial
28961 data pointsPreferred orientation correction: symmetrized harmonic expansion (Jarvinen, 1993)
Crystal data top
Ca2SiO4β = 94.848 (5)°
Mr = 172.24V = 785.00 (7) Å3
Monoclinic, P21/cZ = 8
a = 8.2127 (5) ÅSynchrotron radiation, λ = 1.598 Å
b = 9.7930 (4) ÅT = 298 K
c = 9.7954 (5) Åflat sheet, 29 × 29 mm
Data collection top
MDS, 2-axis, multiple-detector system
diffractometer
Scan method: step
Specimen mounting: Sample was mounted on a glass specimen holder.2θmin = 10°, 2θmax = 155°, 2θstep = 0.005°
Data collection mode: reflection
Refinement top
Rp = 0.084RBragg = 0.070
Rwp = 0.116χ2 = 5.198
Rexp = 0.05128961 data points
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Ca10.8258 (3)0.4210 (2)0.0729 (2)0.0160
Ca20.6621 (3)0.4181 (2)0.4121 (2)0.0160
Ca30.3760 (3)0.2889 (2)0.0816 (2)0.0160
Ca40.9081 (3)0.0681 (2)0.2068 (2)0.0160
Si10.0221 (4)0.2959 (3)0.4326 (3)0.0137
Si20.4618 (4)0.5757 (3)0.2026 (3)0.0137
O10.8768 (7)0.2993 (6)0.5287 (7)0.0175
O20.9625 (8)0.3647 (5)0.2856 (7)0.0175
O30.0641 (8)0.1350 (5)0.4077 (7)0.0175
O40.1831 (7)0.3873 (5)0.5038 (6)0.0175
O50.5894 (9)0.4557 (5)0.1682 (6)0.0175
O60.2903 (9)0.5091 (5)0.1502 (6)0.0175
O70.4982 (7)0.7130 (5)0.1283 (7)0.0175
O80.4557 (7)0.5955 (5)0.3702 (7)0.0175

Experimental details

Crystal data
Chemical formulaCa2SiO4
Mr172.24
Crystal system, space groupMonoclinic, P21/c
Temperature (K)298
a, b, c (Å)8.2127 (5), 9.7930 (4), 9.7954 (5)
β (°) 94.848 (5)
V3)785.00 (7)
Z8
Radiation typeSynchrotron, λ = 1.598 Å
Specimen shape, size (mm)Flat sheet, 29 × 29
Data collection
DiffractometerMDS, 2-axis, multiple-detector system
diffractometer
Specimen mountingSample was mounted on a glass specimen holder.
Data collection modeReflection
Scan methodStep
2θ values (°)2θmin = 10 2θmax = 155 2θstep = 0.005
Refinement
R factors and goodness of fitRp = 0.084, Rwp = 0.116, Rexp = 0.051, RBragg = 0.070, χ2 = 5.198
No. of data points28961
No. of parameters?
No. of restraints?

Computer programs: WPPF(ver.3.00), DATAPRO(ver.2.00), DSS(ver.1.00), PFLS(ver.5.00), Ball&Stick.

 

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