Ytterbium cobalt gallium oxide, YbCoGaO₄, as grown by the floating zone technique

Single crystals of YbCoGaO₄ have been grown for the first time by the optical floating zone technique and characterized by X-ray diffraction at room temperature. Atomic parameters were refined in space group Rm. The structure is isomorphous with that of other materials belonging to the YbFe₂O₄ family. Magnetic measurements suggest spin glass behavior with an ordering temperature around 20 K. The electrical resistivity of the material was measured. The site symmetry of all the atoms is 3m.

Key indicators

• Single-crystal X-ray study
• T = 299 K
• Mean [sigma](Please check) = 0.000 Å
• R factor = 0.027
• wR factor = 0.062
• Data-to-parameter ratio = 13.4

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level A:



ABSTM_02  Alert A Crystal and compound unsuitable for non-numerical
          corrections. Product of mu and tmid > 3.0
           Value of mu given =    39.976 tmid =     0.160

Author response: The sample used for the experiment was a ten micron flake from the bulk sample. The equitorial edges were not natural faces. An analytical face correction using approximate faces and distances in Sheldrick's XPREP did not provide as good a correction (based on R(int)) as did the emperical correction from SADABS. The volume of the sample could have been reduced, but this would have prevented the collection of high resolution data.

 Alert Level B:



SYMMS_01  Alert B The cell setting should be one of the following
          *  triclinic
          *  monoclinic
          *  orthorhombic
          *  tetragonal
          *  rhombohedral
          *  trigonal
          *  hexagonal
          *  cubic
          Cell setting given = Rombohedral


 1 Alert Level A = Potentially serious problem

 1 Alert Level B = Potential problem

 0 Alert Level C = Please check

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S1. Comment

Single crystals of YbCoGaO₄ have been structurally characterized. The refined structure is similar to that of other materials belonging to YbFe₂O₄ family (Cava et al., 1998). Yb is bounded to six O atoms and is found in layers of flattened edge-shared octahedra. It is slightly disordered in the c direction. Five-coordinate Co and Ga atoms are statistically distributed in a double layer of face-shared trigonal bipyramids interleaving the Yb layers, as shown in Fig. 1. These alternating Yb and Co,Ga layers exhibit a corner-shared stacking in the direction of the c axis. The electron microprobe chemical analysis (EPMA) confirms the 1:1 distribution of Co and Ga on the Fe site. Magnetic measurements suggest spin glass behavior with ordering temperature around 20 K. Electrical conductivity was found to be of the order of 105 A m and anisotropic.

S2. Experimental

Single crystals of the YbCoGaO₄ were grown by floating zone technique for the first time. 99.999% pure reagents were used, preannealed before mixing. The growth rate was 1.7 mm h^-1, rotation used was 30 r.p..m for the feed rod and 25 r.p.m. for the seed rod. The total growth was 41.5 mm. Growth was perpendicular to the c axis in the hexagonal system. The experimental details concerning crystal growth and magnetic characterization will be published elsewhere (Dabkowska et al., 2001). Samples for X-ray structure determination and electron microprobe were cut from the top part of the grown rod. Crushed crystals were examined using a Guinier-Haag camera, with Cu Kα₁ radiation and silicon as an internal standard. Intensity and peak positions were determined using a film scanner (LS-20 Kej Instruments, Sweden). The pattern was indexed on the basis of the hexagonal cell. The lattice constant were refined using LSUDF program and the results are in good agreement with both powder diffraction data (Kimizuka & Takayama, 1982) and the single-crystal measurement given in the Crystal Data Table.

S3. Refinement

Refinement of the structure required a 50:50 distribution of Co and Ga on the same site, with common coordinates and displacement parameters. The Yb z coordinate refined slightly off the 3 m site, improving the displacement parameter refinement and residuals. The relatively large anisotropic displacement parameters for O2 are likely a result of the variation in coordination at the Co/Ga site. The sample used for the experiment was a 10 µm flake from the bulk sample. The equatorial edges were not natural faces. An analytical face correction using approximate faces and distances in Sheldrick's XPREP (Sheldrick, 1997) did not provide as good a correction (based on R_int) as did the empirical correction from SADABS (Sheldrick, 2000). The volume of the sample could have been reduced, but this would have prevented the collection of high-resolution data.

Computing details

Data collection: SMART (Bruker, 1997); cell refinement: SMART; data reduction: SAINT (Bruker, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997a); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997a); molecular graphics: SHELXTL (Sheldrick, 1997b); software used to prepare material for publication: SHELXTL.

Figures

Fig. 1. 90% displacement ellipsoid plot of the oxide layers as viewed normal to the c axis.

(I)

Crystal data

YbCoGaO4	F(000) = 480
Mr = 365.69	Dx = 7.174 Mg m^−3
Rombohedral, R3m	Melting point: 1750 K K
a = 3.4165 (1) Å	Mo Kα radiation, λ = 0.71073 Å
b = 3.4165 (1) Å	Cell parameters from 1391 reflections
c = 25.122 (1) Å	θ = 2.4–36.2°
α = 90°	µ = 39.98 mm^−1
β = 90°	T = 299 K
γ = 120°	Plate, black
V = 253.95 (2) Å^3	0.22 × 0.16 × 0.01 mm
Z = 3

Data collection

CCD diffractometer	187 independent reflections
Radiation source: rotating anode	178 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.047
ϕ and ω scans	θmax = 36.2°, θmin = 2.4°
Absorption correction: multi-scan (SADABS; Sheldrick, 2000)	h = −4→5
Tmin = 0.023, Tmax = 0.142	k = −5→4
1932 measured reflections	l = −40→37

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)] = 0.027	w = 1/[σ^2(Fo^2) + (0.0345P)^2 + 4.4469P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.062	(Δ/σ)max < 0.001
S = 1.16	Δρmax = 2.94 e Å^−3
187 reflections	Δρmin = −2.88 e Å^−3
14 parameters	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.049 (4)

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)
Yb1	0.0000	0.0000	0.0048 (3)	0.0037 (10)	0.50
Co1	0.0000	0.0000	0.21469 (4)	0.0028 (3)	0.50
Ga1	0.0000	0.0000	0.21469 (4)	0.0028 (3)	0.50
O1	0.0000	0.0000	0.2913 (3)	0.0058 (11)
O2	0.0000	0.0000	0.1293 (4)	0.0133 (14)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Yb1	0.0006 (3)	0.0006 (3)	0.010 (3)	0.00032 (13)	0.000	0.000
Co1	0.0033 (3)	0.0033 (3)	0.0020 (6)	0.00164 (16)	0.000	0.000
Ga1	0.0033 (3)	0.0033 (3)	0.0020 (6)	0.00164 (16)	0.000	0.000
O1	0.0069 (15)	0.0069 (15)	0.003 (3)	0.0035 (7)	0.000	0.000
O2	0.0131 (19)	0.0131 (19)	0.014 (4)	0.0065 (10)	0.000	0.000

Geometric parameters (Å, º)

Yb1—O1^i	2.182 (4)	Co1—O2^i	1.9907 (12)
Yb1—O1^ii	2.296 (6)	Co1—O2	2.144 (9)
Co1—O1	1.926 (7)
O1^i—Yb1—O1^iii	103.0 (3)	Co1—O1—Yb1^i	115.3 (2)
O1^i—Yb1—O1^ii	174.5 (4)	Yb1^i—O1—Yb1^iii	103.0 (3)
O1^iv—Yb1—O1^ii	80.3 (2)	Co1—O1—Yb1^vi	120.8 (3)
O1^ii—Yb1—O1^v	96.1 (3)	Yb1^i—O1—Yb1^vi	5.5 (4)
O1—Co1—O2^i	97.8 (3)	Yb1^iii—O1—Yb1^vi	99.7 (2)
O2^iii—Co1—O2^i	118.21 (12)	Yb1^vi—O1—Yb1^vii	96.1 (3)
O1—Co1—O2	180.000 (1)	Co1^iii—O2—Co1^i	118.21 (12)
O2^i—Co1—O2	82.2 (3)	Co1^iv—O2—Co1	97.8 (3)
O1—Co1—Yb1^i	34.60 (8)

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