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We report the crystal structure and electron density of samarium titanium oxysulfide, Sm2Ti2S2O4.9, photocatalyst obtained through the Rietveld analysis, maximum-entropy method (MEM) and MEM-based pattern fitting of the high-resolution synchrotron powder diffraction data taken at 298.7 K. The Sm2Ti2S2O4.9 has a tetragonal structure with the space group I4/mmm. Refined occupancy factors at the `equatorial' O1 and `apical' O2 sites were 0.994 (3) and 0.944 (12), respectively, which strongly suggest oxygen deficiency at the O2 site. Electron-density analyses based on the synchrotron diffraction data of Sm2Ti2S2O4.9 in combination with density-functional theory (DFT) calculations of stoichiometric Sm2Ti2S2O5 reveal covalent bonds between Ti and O atoms, while the Sm and S atoms are more ionic. The presence of S 3p and O 2p orbitals results in increased dispersion of the valence band, raising the top of the valence band and making the material active at visible wavelengths. The present DFT calculations of stoichiometric Sm2Ti2S2O5 indicate the possibility of overall splitting of water, although Sm2Ti2S2O4.9 works as a visible-light-responsive photocatalyst in aqueous solutions only in the presence of sacrificial electron donors or acceptors. The oxygen deficiency and cocatalyst seem to be factors affecting the catalytic activity.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768108007532/og5028sup1.cif
Contains datablocks global, I

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0108768108007532/og5028sup2.rtv
Contains datablocks global, I

Computing details top

Data collection: RIGAKU software (Toraya et al., 1996); cell refinement: RIETAN-2000 (Izumi and Ikeda, 2000); program(s) used to solve structure: RIETAN-2000; program(s) used to refine structure: RIETAN-2000; molecular graphics: VESTA [Momma and Izumi (2006)].

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samarium titanium oxysulfide top
Crystal data top
O9.84S4Sm4Ti4Z = 1
Mr = 1078.61Dx = 5.342 Mg m3
Tetragonal, I4/mmmSynchrotron radiation, λ = 1.20643 Å
Hall symbol: -I 4 2T = 299 K
a = 3.82123 (2) Åyellow to yellowish-green
c = 22.96371 (12) Åcircular flat plate, 20 × 0.5 mm
V = 335.31 (1) Å3Specimen preparation: Prepared at 1173 K and 100 kPa, cooled at 10 K min1
Data collection top
A multiple-detector system with Ge(111) analyzer crystals, Soller slits and scintillation counters (Toraya et al., 1996)
diffractometer
Data collection mode: reflection
Ge(111) analyzer crystals monochromatorScan method: step
Specimen mounting: flat specimen2θmin = 7.051°, 2θmax = 154.887°, 2θstep = 0.01°
Refinement top
Rp = 0.054Excluded region(s): none
Rwp = 0.069Profile function: Split Pearson (Toraya, 1990)
Rexp = ?10 parameters
χ2 = 2.434
? data points
Crystal data top
O9.84S4Sm4Ti4V = 335.31 (1) Å3
Mr = 1078.61Z = 1
Tetragonal, I4/mmmSynchrotron radiation, λ = 1.20643 Å
a = 3.82123 (2) ÅT = 299 K
c = 22.96371 (12) Åcircular flat plate, 20 × 0.5 mm
Data collection top
A multiple-detector system with Ge(111) analyzer crystals, Soller slits and scintillation counters (Toraya et al., 1996)
diffractometer
Scan method: step
Specimen mounting: flat specimen2θmin = 7.051°, 2θmax = 154.887°, 2θstep = 0.01°
Data collection mode: reflection
Refinement top
Rp = 0.054χ2 = 2.434
Rwp = 0.069? data points
Rexp = ?10 parameters
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzBiso*/BeqOcc. (<1)
Sm000.33382 (1)0.253 (9)*
Ti000.07819 (4)0.309 (15)*
S000.20364 (7)0.360 (18)*
O100.500000.09734 (9)0.53 (5)*0.994 (3)
O20000.73 (11)*0.944 (12)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Sm0.0032020.0032020.003202000
Ti0.0039120.0039120.003912000
S0.0045640.0045640.004564000
O10.0067000.0067000.006700000
O20.0092670.0092670.009267000

Experimental details

Crystal data
Chemical formulaO9.84S4Sm4Ti4
Mr1078.61
Crystal system, space groupTetragonal, I4/mmm
Temperature (K)299
a, c (Å)3.82123 (2), 22.96371 (12)
V3)335.31 (1)
Z1
Radiation typeSynchrotron, λ = 1.20643 Å
Specimen shape, size (mm)Circular flat plate, 20 × 0.5
Data collection
DiffractometerA multiple-detector system with Ge(111) analyzer crystals, Soller slits and scintillation counters (Toraya et al., 1996)
diffractometer
Specimen mountingFlat specimen
Data collection modeReflection
Scan methodStep
2θ values (°)2θmin = 7.051 2θmax = 154.887 2θstep = 0.01
Refinement
R factors and goodness of fitRp = 0.054, Rwp = 0.069, Rexp = ?, χ2 = 2.434
No. of data points?
No. of parameters10
No. of restraints?

Computer programs: RIGAKU software (Toraya et al., 1996), RIETAN-2000 (Izumi and Ikeda, 2000), RIETAN-2000, VESTA [Momma and Izumi (2006)].

 

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