Sc₂TiO₅, an entropy-stabilized pseudobrookite-type compound

Discandium(III) titanate(IV), Sc₂TiO₅, prepared by the flux method, has a pseudobrookite-type structure. The Sc and Ti atoms are partially disordered on the two octahedrally coordinated metal (M) sites (Wyckoff designations 8f and 4c in space group Cmcm). The most probable cation distribution suggests the approximate structural formula ^[8f](Sc_0.6,Ti_0.4)₂^[4c](Sc_0.8Ti_0.2)O₅, in agreement with earlier observations of a preference of Ti for the more distorted 8f site in isotypic A^III₂B^IVO₅ compounds. The average M-O bond lengths for the 8f and 4c sites are 2.059 and 2.095 Å, respectively. The strongly distorted octahedra share edges to form trioctahedral units, which are linked into infinite double chains along c. Further sharing of octahedral edges results in a three-dimensional framework. All atoms are on special positions. An Al-bearing variety of Sc₂TiO₅ has Al preferentially incorporated on the 4c site.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](Please check) = 0.000 Å
• R factor = 0.016
• wR factor = 0.048
• Data-to-parameter ratio = 15.5

checkCIF results

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ADDSYM reports no extra symmetry

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Computing details

Data collection: COLLECT (Nonius, 2002); cell refinement: HKL SCALEPACK (Otwinowski & Minor, 1997); data reduction: HKL DENZO (Otwinowski & Minor, 1997) and SCALEPACK; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ATOMS (Shape Software, 1999) and ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: SHELXL97.

discandium(III) titanate(IV)

Crystal data

Sc2TiO5	F(000) = 416
Mr = 217.82	Dx = 3.605 Mg m^−3
Orthorhombic, Cmcm	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2c 2	Cell parameters from 454 reflections
a = 3.851 (1) Å	θ = 2.0–32.6°
b = 10.131 (2) Å	µ = 5.13 mm^−1
c = 10.287 (2) Å	T = 293 K
V = 401.34 (15) Å^3	Plate, colorless
Z = 4	0.10 × 0.10 × 0.03 mm

Data collection

Nonius KappaCCD diffractometer	435 independent reflections
Radiation source: fine-focus sealed tube	416 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.008
φ and ω scans	θmax = 32.5°, θmin = 4.0°
Absorption correction: multi-scan (HKL SCALEPACK; Otwinowski & Minor, 1997)	h = −5→5
Tmin = 0.628, Tmax = 0.883	k = −15→15
728 measured reflections	l = −15→15

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.016	w = 1/[σ^2(Fo^2) + (0.02P)^2 + 0.83P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.048	(Δ/σ)max < 0.001
S = 1.20	Δρmax = 0.85 e Å^−3
435 reflections	Δρmin = −0.85 e Å^−3
28 parameters	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.0143 (12)

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Ti1	0.0000	0.36444 (3)	0.43775 (3)	0.00474 (12)	0.40
Sc1	0.0000	0.36444 (3)	0.43775 (3)	0.00474 (12)	0.60
Ti2	0.0000	0.30752 (4)	0.7500	0.00549 (13)	0.20
Sc2	0.0000	0.30752 (4)	0.7500	0.00549 (13)	0.80
O1	0.0000	0.45339 (14)	0.61424 (15)	0.0146 (3)
O2	−0.5000	0.23222 (19)	0.7500	0.0088 (3)
O3	0.0000	0.19241 (13)	0.57087 (13)	0.0096 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ti1	0.00496 (17)	0.00393 (17)	0.00533 (17)	0.000	0.000	−0.00004 (9)
Sc1	0.00496 (17)	0.00393 (17)	0.00533 (17)	0.000	0.000	−0.00004 (9)
Ti2	0.0059 (2)	0.0061 (2)	0.0044 (2)	0.000	0.000	0.000
Sc2	0.0059 (2)	0.0061 (2)	0.0044 (2)	0.000	0.000	0.000
O1	0.0159 (7)	0.0184 (7)	0.0095 (6)	0.000	0.000	0.0059 (5)
O2	0.0078 (8)	0.0112 (8)	0.0075 (7)	0.000	0.000	0.000
O3	0.0114 (6)	0.0092 (6)	0.0082 (6)	0.000	0.000	−0.0002 (4)

Geometric parameters (Å, º)

Ti1—O1^i	1.9215 (15)	Sc2—O1^iv	2.0333 (14)
Ti1—O3^ii	2.0117 (6)	Sc2—O1	2.0333 (14)
Ti1—O3^iii	2.0117 (6)	Sc2—O2	2.0711 (9)
Ti1—O1	2.0269 (16)	Sc2—O2^v	2.0711 (9)
Ti1—O2^ii	2.1655 (10)	Sc2—O3	2.1807 (14)
Ti1—O3	2.2164 (14)	Sc2—O3^iv	2.1807 (14)
O1^i—Ti1—O3^ii	105.23 (4)	Ti1^i—O1—Ti2	152.78 (9)
O1^i—Ti1—O3^iii	105.23 (4)	Ti1—O1—Ti2	106.98 (7)
O3^ii—Ti1—O3^iii	146.32 (8)	Ti2—O2—Sc2^vi	136.78 (10)
O1^i—Ti1—O1	79.76 (7)	Ti2—O2—Ti2^vi	136.78 (10)
O3^ii—Ti1—O1	99.60 (4)	Ti2—O2—Ti1^ii	99.588 (9)
O3^iii—Ti1—O1	99.60 (4)	Sc2^vi—O2—Ti1^ii	99.588 (9)
O1^i—Ti1—O2^ii	100.73 (7)	Ti2^vi—O2—Ti1^ii	99.588 (9)
O3^ii—Ti1—O2^ii	80.28 (4)	Ti2—O2—Sc1^ii	99.588 (9)
O3^iii—Ti1—O2^ii	80.28 (4)	Sc2^vi—O2—Sc1^ii	99.588 (9)
O1—Ti1—O2^ii	179.51 (6)	Ti2^vi—O2—Sc1^ii	99.588 (9)
O1^i—Ti1—O3	158.00 (6)	Ti2—O2—Sc1^vii	99.588 (9)
O3^ii—Ti1—O3	78.59 (4)	Sc2^vi—O2—Sc1^vii	99.588 (9)
O3^iii—Ti1—O3	78.59 (4)	Ti2^vi—O2—Sc1^vii	99.588 (9)
O1—Ti1—O3	78.24 (5)	Ti1^ii—O2—Sc1^vii	126.23 (9)
O2^ii—Ti1—O3	101.27 (6)	Sc1^ii—O2—Sc1^vii	126.23 (9)
O1^iv—Ti2—O1	86.76 (9)	Ti2—O2—Ti1^vii	99.588 (9)
O1^iv—Ti2—O2	105.53 (4)	Sc2^vi—O2—Ti1^vii	99.588 (9)
O1—Ti2—O2	105.53 (4)	Ti2^vi—O2—Ti1^vii	99.588 (9)
O1^iv—Ti2—O2^v	105.53 (4)	Ti1^ii—O2—Ti1^vii	126.23 (9)
O1—Ti2—O2^v	105.53 (4)	Sc1^ii—O2—Ti1^vii	126.23 (9)
O2—Ti2—O2^v	136.78 (10)	Sc1^ii—O3—Sc1^iii	146.32 (8)
O1^iv—Ti2—O3	165.71 (6)	Ti1^ii—O3—Sc1^iii	146.32 (8)
O1—Ti2—O3	78.95 (6)	Sc1^ii—O3—Ti1^iii	146.32 (8)
O2—Ti2—O3	78.64 (3)	Ti1^ii—O3—Ti1^iii	146.32 (8)
O2^v—Ti2—O3	78.64 (3)	Sc1^ii—O3—Ti2	100.97 (4)
O1^iv—Ti2—O3^iv	78.95 (6)	Ti1^ii—O3—Ti2	100.97 (4)
O1—Ti2—O3^iv	165.71 (6)	Sc1^iii—O3—Ti2	100.97 (4)
O2—Ti2—O3^iv	78.64 (3)	Ti1^iii—O3—Ti2	100.97 (4)
O2^v—Ti2—O3^iv	78.64 (3)	Sc1^ii—O3—Ti1	101.41 (4)
O3—Ti2—O3^iv	115.35 (8)	Ti1^ii—O3—Ti1	101.41 (4)
Sc1^i—O1—Ti1	100.24 (7)	Sc1^iii—O3—Ti1	101.41 (4)
Ti1^i—O1—Ti1	100.24 (7)	Ti1^iii—O3—Ti1	101.41 (4)
Sc1^i—O1—Ti2	152.78 (9)	Ti2—O3—Ti1	95.83 (6)

Symmetry codes: (i) −x, −y+1, −z+1; (ii) −x−1/2, −y+1/2, −z+1; (iii) −x+1/2, −y+1/2, −z+1; (iv) x, y, −z+3/2; (v) x+1, y, z; (vi) x−1, y, z; (vii) −x−1/2, −y+1/2, z+1/2.