research papers
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 -Ca2SiO4 (= -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 -C2S, having eightfold to tenfold coordination sites for the Ca atoms.
Keywords: dicalcium silicate; structural transformation; simulated annealing; Rietveld refinement; synchrotron radiation powder diffraction.
Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768102005189/ck0012sup1.cif | |
Rietveld powder data file (CIF format) https://doi.org/10.1107/S0108768102005189/ck0012sup2.rtv |
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.
dicalcium silicate top
Crystal data top
Ca2SiO4 | Z = 8 |
Mr = 172.24 | F(000) = 688 |
Monoclinic, P21/c | Dx = 2.91 Mg m−3 |
a = 8.2127 (5) Å | Synchrotron radiation, λ = 1.598 Å |
b = 9.7930 (4) Å | T = 298 K |
c = 9.7954 (5) Å | Particle morphology: plate-like |
β = 94.848 (5)° | white |
V = 785.00 (7) Å3 | flat sheet, 29 × 29 mm |
Data collection top
MDS, 2-axis, multiple-detector system diffractometer | Data collection mode: reflection |
Radiation source: synchrotron radiation | Scan method: step |
Double-crystal Si(111) monochromator | 2θmin = 10°, 2θmax = 155°, 2θstep = 0.005° |
Specimen mounting: Sample was mounted on a glass specimen holder. |
Refinement top
Rp = 0.084 | Excluded region(s): none |
Rwp = 0.116 | Profile function: pseudo-Voigt |
Rexp = 0.051 | 1/(Yi) |
RBragg = 0.070 | |
χ2 = 5.198 | Background function: polynomial |
28961 data points | Preferred orientation correction: symmetrized harmonic expansion (Jarvinen, 1993) |
Crystal data top
Ca2SiO4 | β = 94.848 (5)° |
Mr = 172.24 | V = 785.00 (7) Å3 |
Monoclinic, P21/c | Z = 8 |
a = 8.2127 (5) Å | Synchrotron radiation, λ = 1.598 Å |
b = 9.7930 (4) Å | T = 298 K |
c = 9.7954 (5) Å | flat 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 |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
x | y | z | Uiso*/Ueq | ||
Ca1 | 0.8258 (3) | 0.4210 (2) | 0.0729 (2) | 0.0160 | |
Ca2 | 0.6621 (3) | 0.4181 (2) | 0.4121 (2) | 0.0160 | |
Ca3 | 0.3760 (3) | 0.2889 (2) | 0.0816 (2) | 0.0160 | |
Ca4 | 0.9081 (3) | 0.0681 (2) | 0.2068 (2) | 0.0160 | |
Si1 | 0.0221 (4) | 0.2959 (3) | 0.4326 (3) | 0.0137 | |
Si2 | 0.4618 (4) | 0.5757 (3) | 0.2026 (3) | 0.0137 | |
O1 | 0.8768 (7) | 0.2993 (6) | 0.5287 (7) | 0.0175 | |
O2 | 0.9625 (8) | 0.3647 (5) | 0.2856 (7) | 0.0175 | |
O3 | 0.0641 (8) | 0.1350 (5) | 0.4077 (7) | 0.0175 | |
O4 | 0.1831 (7) | 0.3873 (5) | 0.5038 (6) | 0.0175 | |
O5 | 0.5894 (9) | 0.4557 (5) | 0.1682 (6) | 0.0175 | |
O6 | 0.2903 (9) | 0.5091 (5) | 0.1502 (6) | 0.0175 | |
O7 | 0.4982 (7) | 0.7130 (5) | 0.1283 (7) | 0.0175 | |
O8 | 0.4557 (7) | 0.5955 (5) | 0.3702 (7) | 0.0175 |
Experimental details
Crystal data | |
Chemical formula | Ca2SiO4 |
Mr | 172.24 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 298 |
a, b, c (Å) | 8.2127 (5), 9.7930 (4), 9.7954 (5) |
β (°) | 94.848 (5) |
V (Å3) | 785.00 (7) |
Z | 8 |
Radiation type | Synchrotron, λ = 1.598 Å |
Specimen shape, size (mm) | Flat sheet, 29 × 29 |
Data collection | |
Diffractometer | MDS, 2-axis, multiple-detector system diffractometer |
Specimen mounting | Sample was mounted on a glass specimen holder. |
Data collection mode | Reflection |
Scan method | Step |
2θ values (°) | 2θmin = 10 2θmax = 155 2θstep = 0.005 |
Refinement | |
R factors and goodness of fit | Rp = 0.084, Rwp = 0.116, Rexp = 0.051, RBragg = 0.070, χ2 = 5.198 |
No. of data points | 28961 |
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.