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Titanium dioxide is an inexpensive wide-gap highly ionic semiconductor with striking photocatalytic capabilities in several heterogeneous photoredox reactions. A small crystal size is desirable to maximize the surface area, since photocatalytic reactions occur at the surface of a photocatalyst. Presented here are the synthesis and microstructural characterization of 4 at.% Sc-doped TiO2 (4SDT) prepared by water-based co-precipitation. The crystal structure of 4SDT was examined via in situ high-temperature powder X-ray diffraction experiments from 25 to 1200°C. Rietveld analysis revealed single-phase anatase up to 875°C, while at 900°C the anatase-to-rutile phase transformation occurred and at higher temperatures additional reflections of Sc-rich phases (Sc2TiO5 from 975°C and Ti3Sc4O12 or Sc2O3 at 1200°C) were observed. Debye function analysis (DFA) was applied to model the total scattering pattern directly in reciprocal space, allowing the reconstruction of Ti vacancies. Both Rietveld and DFA methods were applied to estimate the nanocrystallite size and shape with consistent growth in crystallite size with temperature: an ellipsoid shape with equatorial ∼4.7 nm / axial (001) ∼6.9 nm at 25°C to equatorial ∼27.9 nm / axial (001) ∼39.6 nm at 900°C refined by Rietveld analysis, versus a cylinder shape with Da,b = 4.3 nm and size dispersion σab = 1.5 nm, Lc = 4.9 nm and σc = 2.3 nm at 25°C to Da,b = 21.4 nm, σab = 8.3 nm, Lc = 23.9 and σc = 10.9 nm at 900°C estimated by DFA. The microstructural changes obtained by Rietveld and DFA methods were supported by high-resolution transmission electron microscopy image analysis, as well as by the less direct nitrogen sorption techniques that provide information on the size of non-agglomerated and dense particles. The Ti site-occupancy factor showed a linear increase from 0.6–0.8 at 25°C to unity at 900°C for anatase, and from ∼0.7 at 900°C to unity at 1200°C for rutile, via Rietveld analysis and DFA.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600576720012017/kc5111sup1.cif
Contains datablocks TiSc02_875C_publ, TiSc02_875C_overall, TiSc02_875C_phase_0, TiSc02_875C_phase_1, TiSc02_875C_pwd_0

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Portable Document Format (PDF) file https://doi.org/10.1107/S1600576720012017/kc5111sup2.pdf
Detailed results of XRD Rietveld analysis and DFA, lattice parameters of Pt, HRTEM and SAED analyses

Computing details top

(TiSc02_875C_phase_0) top
Crystal data top
OSc0.02Ti0.475c = 9.5999 (6) Å
Mr = 39.63V = 138.65 (2) Å3
Tetragonal, I41/amdZ = 8
a = 3.8003 (2) ÅDx = 3.797 Mg m3
Refinement top
Profile function: Crystallite size in microns with "uniaxial" model: anisotropic axis is [0, 0, 1] parameters: equatorial size, axial size, G/L mix 0.02271(18), 0.0299(6), 1.000, Microstrain, "isotropic" model (106 * delta Q/Q) parameters: Mustrain, G/L mix 347.184, 1.000,Preferred orientation correction: March-Dollase correction coef. = 1.000 axis = [0, 0, 1]
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Ti10.000000.250000.125000.011*0.949 (10)
O20.000000.250000.919180.014*
SC10.000000.250000.125000.011300*0.040
Geometric parameters (Å, º) top
Ti1—O2i1.9759SC1—O2ii1.9469
Ti1—O2ii1.9469SC1—O2iii1.9469
Ti1—O2iii1.9469SC1—O2iv1.9469
Ti1—O2iv1.9469SC1—O2v1.9469
Ti1—O2v1.9469SC1—O2vi1.9759
Ti1—O2vi1.9759SC1—SC1x3.0611
O2—Ti1vii1.9759SC1—SC1xi3.0611
O2—Ti1viii1.9469SC1—SC1xii3.0611
O2—Ti1ix1.9469SC1—SC1xiii3.0611
SC1—O2i1.9759
O2i—Ti1—O2ii102.581Ti1viii—O2—Ti1ix154.838
O2i—Ti1—O2iii102.581O2i—SC1—O2ii102.581
O2ii—Ti1—O2iii154.838O2i—SC1—O2iii102.581
O2i—Ti1—O2iv77.419O2ii—SC1—O2iii154.838
O2ii—Ti1—O2iv92.72O2i—SC1—O2iv77.419
O2iii—Ti1—O2iv92.72O2ii—SC1—O2iv92.72
O2i—Ti1—O2v77.419O2iii—SC1—O2iv92.72
O2ii—Ti1—O2v92.72O2i—SC1—O2v77.419
O2iii—Ti1—O2v92.72O2ii—SC1—O2v92.72
O2iv—Ti1—O2v154.838O2iii—SC1—O2v92.72
O2i—Ti1—O2vi180O2iv—SC1—O2v154.838
O2ii—Ti1—O2vi77.419O2i—SC1—O2vi180
O2iii—Ti1—O2vi77.419O2ii—SC1—O2vi77.419
O2iv—Ti1—O2vi102.581O2iii—SC1—O2vi77.419
O2v—Ti1—O2vi102.581O2iv—SC1—O2vi102.581
Ti1vii—O2—Ti1viii102.581O2v—SC1—O2vi102.581
Ti1vii—O2—Ti1ix102.581
Symmetry codes: (i) x, y, z1; (ii) y3/4, x1/4, z3/4; (iii) y+1/4, x1/4, z3/4; (iv) x, y1, z+1; (v) x, y, z+1; (vi) y+3/4, x+3/4, z+9/4; (vii) x, y, z+1; (viii) y+1/4, x3/4, z+3/4; (ix) y+1/4, x+1/4, z+3/4; (x) y3/4, x1/4, z+1/4; (xi) y+1/4, x1/4, z+1/4; (xii) y+1/4, x3/4, z1/4; (xiii) y+1/4, x+1/4, z1/4.
(TiSc02_875C_phase_1) top
Crystal data top
PtV = 62.03 (1) Å3
Mr = 195.09Z = 4
Cubic, Fm3mDx = 20.892 Mg m3
a = 3.95845 (14) Å
Refinement top
Profile function: Crystallite size in microns with "isotropic" model: parameters: Size, G/L mix 0.317(17), 1.000, Microstrain, "isotropic" model (106 * delta Q/Q) parameters: Mustrain, G/L mix 929.343, 1.000,Preferred orientation correction: March-Dollase correction coef. = 1.000 axis = [0, 0, 1]
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Pt10.000000.000000.000000.002*
 

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