Ca_0.8Y_2.4Sn_0.8O₆, a quaternary oxide with mixed occupations of Ca/Y and Y/Sn

A new quaternary oxide, calcium yttrium stannate, Ca_0.8Y_2.4Sn_0.8O₆, is isostructural with Mg₃TeO₆ (trigonal, R). The empirical formula can be expressed as (Ca_0.2667Y_0.7333)₆(Y_0.4Sn_0.6)SnO₁₂. The Ca/Y site has a distorted coordination octa­hedron of O atoms, with Ca/Y-O distances ranging from 2.227 (3) to 2.350 (3) Å, while the octa­hedra of O atoms that coordinate to the Sn and Y/Sn sites are nearly regular, with an Sn-O distance of 2.066 (2) Å and a Y/Sn-O distance of 2.147 (3) Å.

S1. Comment

New quaternary compounds have recently been found in addition to the previously known CaO–Y₂O₃–SiO₂ (Nagasawa et al., 1998) and CaO–Y₂O₃–GeO₂ systems (Yamane et al., 2006). Since no quaternary compound had been reported for the CaO–Y₂O₃–SnO₂ system, we have carried out a materials survey for this system. As a result, the new quaternary compound Ca_0.8Y_2.4Sn_0.8O₆ was prepared by solid-state reaction. The crystal structure of Ca_0.8Y_2.4Sn_0.8O₆ reveals that it has the same structure type as Mg₃TeO₆, in which Te atoms are located at the 3a and 3b special positions in space group R3, while the Mg and O atoms are at general (18f) positions (Newnham et al., 1970, Schulz & Bayer, 1971).

In the starting model, Sn and Y atoms were placed statistically at the 3a and 3b sites and Ca and Y atoms at an 18f site. The occupancies at the Ca1/Y1, Sn1 and Y2/Sn2 sites were refined to values of 0.270 (3)/0.730 (3), 0.996 (3) and 0.404 (4)/0.596 (4), respectively, giving the Ca:Y:Sn molar ratio 1:3:1. This ratio agrees with the initial molar ratio of metal elements in the mixture used in the synthesis. For the final refinement, the occupation parameters were fixed at values of 0.2667/0.7333, 1.0 and 0.40/0.60 for Ca1/Y1, Sn1 and Y2/Sn2. The structure formula of Ca_0.8Y_2.4Sn_0.8O₆ can be expressed as (Ca_0.2667Y_0.7333)₆(Y_0.4Sn_0.6)SnO₁₂.

Fig. 1 shows the O-atom coordination surrounding the Ca1/Y1 and Sn sites. The extended structure, illustrated by the Sn1- and Y2/Sn2-centered oxygen octahedra, is shown in Fig. 2. Table 1 lists selected interatomic distances and angles. The Sn1—O1 distance in the Sn1(O1)₆ octahedron is 2.066 (2) Å, which is in good agreement with the Sn—O distances (2.061–2.063 Å) reported for CaSnO₃ and SrSnO₃, which have the perovskite-type structure (Vegas et al., 1986). The bond valence sum for Sn1, calculated with the bond valence parameter of Sn^IV—O^II (1.905 Å) was 3.848 (Brese & O'Keeffe, 1991). The value is close to the formal valence of Sn^IV. The Y2/Sn2—O2 distance in the Y2/Sn2(O2)₆ octahedron is 2.147 (3) Å. This value is longer than that in the Sn1(O1)₆ octahedron, consistent with the statistical occupation of Sn and Y atoms in the same site with an occupancy ratio Sn:Y of 0.6:0.4. The Ca1/Y1 site is surrounded by six O atoms in the three O1 and three O2 sites, with Ca1/Y1—O1 and Ca1/Y1—O2 distances in the range 2.227 (3) to 2.350 (3) Å, with an average value of 2.308 Å. The bond valence sum for Ca, calculated with the bond valence parameter of Ca^II—O^II (1.967 Å), is 2.409 and that of Y, with the parameter of Y^III—O^II (2.014 Å), is 2.735. These results agree with a mixed occupation of Ca and Y atoms in the 18f site with a Ca:Y ratio of 0.2667:0.7333.

In the quaternary compounds prepared in the CaO–Y₂O₃–SiO₂ and CaO–Y₂O₃–GeO₂ systems, coordination numbers for Ca and Y range from six to eight, and Si or Ge atoms lie in tetrahedral sites. However, all cations in Ca_0.8Y_2.4Sn_0.8O₆ are in sixfold coordination sites, surrounded by oxygen octahedra. The bond length distortion, octahedral edge length distortion and octahedral angle variance defined by Renner & Lehmann (1986) are 0%, 3.62% and 1.70° for Sn1(O1)₆, 0%, 6.63% and 5.76° for Y2/Sn2(O1)₆, and 5.23%, 10.02% and 25.07° for Ca1/Y1(O1,2)₆, respectively. These values indicate that the Ca1/Y1(O1,2)₆ octahedron is the most distorted in the structure. This octahedron shares an edge of length 2.832 (2) Å with Y2/Sn2(O2)₆, another edge of length 2.815 (4) Å with Sn1(O1)₆, and four edges [2.972 (2)–2.987 (3) Å, average 2.973 Å] with a related Ca1/Y1(O1,2)₆ unit.

S2. Experimental

The starting materials were powders of Y₂O₃ (99.99% purity; Nippon Yttrium), CaCO₃ (99.99% purity; Rare Metallic) and SnO₂ (99.9% purity; Sigma–Aldrich). Y₂O₃ and SnO₂ powders were heated at 1273 K for 6 h before weighing. The powders were weighed and mixed in Ca:Y:Sn molar ratio of 1:3:1. The mixture was pressed into a pellet at 50 MPa and placed on a platinum plate. The polycrystalline sample of Ca_0.8Y_2.4Sn_0.8O₆ was prepared by reaction sintering at 1400 K with an electric furnace in air. After heating at this temperature for 12 h, the sample was cooled to room temperature in the furnace. Grain growth in the sample was observed upon heating at 1773 K for 24 h. A colorless granular single-crystal with a size less than 0.08 × 0.08 × 0.07 mm was selected from the resulting grains.

Computing details

Data collection: PROCESS-AUTO (Rigaku/MSC & Rigaku Corporation, 2005); cell refinement: PROCESS-AUTO; data reduction: CrystalStructure (Rigaku/MSC & Rigaku Corporation, 2005); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ATOMS (Dowty, 1999); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. The arrangement of atomic positions in the structure of Ca0.8Y2.4Sn0.8O6, with 99% probability displacement ellipsoids. Please define all symmetry codes.
	Fig. 2. The crystal structure of Ca0.8Y2.4Sn0.8O6 in a representation using oxygen-centered Sn1 and Y2/Sn2 octahedra.

(I)

Crystal data

Ca0.8O6Sn0.8Y2.4	Dx = 5.051 Mg m^−3
Mr = 436.40	Mo Kα radiation, λ = 0.710747 Å
Trigonal, R3	Cell parameters from 2701 reflections
Hall symbol: -R 3	θ = 3.1–27.5°
a = 9.509 (5) Å	µ = 28.19 mm^−1
c = 10.989 (8) Å	T = 296 K
V = 860.5 (9) Å^3	Granule, colourless
Z = 6	0.08 × 0.08 × 0.07 mm
F(000) = 1186

Data collection

Rigaku R-AXIS RAPID diffractometer	445 independent reflections
Radiation source: fine-focus sealed tube	430 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.053
Detector resolution: 10.00 pixels mm^-1	θmax = 27.5°, θmin = 3.1°
ω scans	h = −11→12
Absorption correction: numerical (ABSCOR; Higashi, 1999)	k = −12→12
Tmin = 0.101, Tmax = 0.123	l = −14→14
2843 measured reflections

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)] = 0.018	w = 1/[σ^2(Fo^2) + 1.9055P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.041	(Δ/σ)max < 0.001
S = 1.18	Δρmax = 0.63 e Å^−3
445 reflections	Δρmin = −0.60 e Å^−3
33 parameters	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.0044 (2)

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)
Ca1	0.26795 (4)	0.22760 (4)	0.29390 (3)	0.00538 (16)	0.2667
Y1	0.26795 (4)	0.22760 (4)	0.29390 (3)	0.00538 (16)	0.7333
Sn1	0.0000	0.0000	0.5000	0.00499 (17)
Y2	0.0000	0.0000	0.0000	0.00420 (18)	0.4
Sn2	0.0000	0.0000	0.0000	0.00420 (18)	0.6
O1	0.0278 (3)	0.1830 (3)	0.3839 (2)	0.0089 (5)
O2	0.2087 (3)	0.1806 (3)	0.0968 (2)	0.0118 (5)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ca1	0.0058 (2)	0.0051 (2)	0.0057 (2)	0.00309 (16)	−0.00002 (13)	−0.00020 (12)
Y1	0.0058 (2)	0.0051 (2)	0.0057 (2)	0.00309 (16)	−0.00002 (13)	−0.00020 (12)
Sn1	0.0046 (2)	0.0046 (2)	0.0058 (3)	0.00229 (10)	0.000	0.000
Y2	0.0039 (2)	0.0039 (2)	0.0048 (3)	0.00195 (11)	0.000	0.000
Sn2	0.0039 (2)	0.0039 (2)	0.0048 (3)	0.00195 (11)	0.000	0.000
O1	0.0100 (12)	0.0053 (11)	0.0107 (13)	0.0034 (10)	0.0006 (9)	0.0027 (9)
O2	0.0153 (13)	0.0168 (13)	0.0082 (13)	0.0117 (12)	−0.0001 (10)	−0.0001 (9)

Geometric parameters (Å, º)

Ca1/Y1—O2	2.227 (3)	Sn1—O1	2.066 (2)
Ca1/Y1—O1^i	2.280 (3)	Sn1—O1^vii	2.066 (2)
Ca1/Y1—O1	2.325 (2)	Sn1—O1^viii	2.066 (2)
Ca1/Y1—O1^ii	2.328 (3)	Y2/Sn2—O2^ix	2.147 (3)
Ca1/Y1—O2^iii	2.335 (3)	Y2/Sn2—O2	2.147 (3)
Ca1/Y1—O2^iv	2.350 (3)	Y2/Sn2—O2^x	2.147 (3)
Sn1—O1^v	2.066 (2)	Y2/Sn2—O2^ii	2.147 (3)
Sn1—O1^vi	2.066 (2)	Y2/Sn2—O2^xi	2.147 (3)
Sn1—O1^ii	2.066 (2)	Y2/Sn2—O2^v	2.147 (3)
O1—Ca1/Y1—O1^ii	74.42 (11)	O1^v—Sn1—O1^viii	94.14 (10)
O1^ii—Ca1/Y1—O2^iii	79.60 (8)	O2—Y2/Sn2—O2^x	82.41 (9)
O1^i—Ca1/Y1—O1	80.37 (8)	O2^ix—Y2/Sn2—O2^ii	82.41 (9)
O1^i—Ca1/Y1—O2^iv	80.27 (8)	O2—Y2/Sn2—O2^xi	82.41 (9)
O1^ii—Ca1/Y1—O2^iv	96.64 (9)	O2^x—Y2/Sn2—O2^v	82.41 (9)
O1—Ca1/Y1—O2^iv	110.38 (9)	O2^ii—Y2/Sn2—O2^xi	82.41 (9)
O1^i—Ca1/Y1—O2^iii	125.35 (8)	O2^ix—Y2/Sn2—O2^v	82.41 (9)
O1^i—Ca1/Y1—O1^ii	151.77 (5)	O2—Y2/Sn2—O2^v	97.59 (9)
O1—Ca1/Y1—O2^iii	153.95 (8)	O2^ii—Y2/Sn2—O2^v	97.59 (9)
O2^iii—Ca1/Y1—O2^iv	74.28 (12)	O2^ix—Y2/Sn2—O2^x	97.59 (9)
O2—Ca1/Y1—O2^iii	80.38 (9)	O2—Y2/Sn2—O2^ii	97.59 (9)
O2—Ca1/Y1—O1^i	92.93 (8)	O2^x—Y2/Sn2—O2^xi	97.59 (9)
O2—Ca1/Y1—O1	104.50 (9)	O2^ix—Y2/Sn2—O2^xi	97.59 (9)
O2—Ca1/Y1—O1^ii	105.40 (9)	Ca1/Y1^iii—O2—Ca1/Y1^xii	97.05 (9)
O2—Ca1/Y1—O2^iv	142.61 (8)	Ca1/Y1^i—O1—Ca1/Y1^v	99.24 (8)
O1^vi—Sn1—O1^viii	85.86 (10)	Ca1/Y1—O2—Ca1/Y1^iii	99.62 (9)
O1^vii—Sn1—O1^viii	85.86 (10)	Ca1/Y1^i—O1—Ca1/Y1	99.63 (8)
O1^vi—Sn1—O1^vii	85.86 (10)	Ca1/Y1—O2—Ca1/Y1^xii	120.13 (11)
O1^ii—Sn1—O1	85.86 (10)	Ca1/Y1—O1—Ca1/Y1^v	124.66 (11)
O1^v—Sn1—O1	85.86 (10)	Sn1—O1—Ca1/Y1^v	96.58 (9)
O1^v—Sn1—O1^ii	85.86 (10)	Sn1—O1—Ca1/Y1	96.68 (9)
O1^vi—Sn1—O1^ii	94.14 (10)	Sn1—O1—Ca1/Y1^i	144.93 (12)
O1^vi—Sn1—O1	94.14 (10)	Y2/Sn2—O2—Ca1/Y1^xii	99.28 (10)
O1^v—Sn1—O1^vii	94.14 (10)	Y2/Sn2—O2—Ca1/Y1^iii	99.75 (9)
O1^ii—Sn1—O1^vii	94.14 (10)	Y2/Sn2—O2—Ca1/Y1	133.03 (12)
O1—Sn1—O1^viii	94.14 (10)

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