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Acta Cryst. (2008). E64, i72    [ doi:10.1107/S1600536808030754 ]

Redetermination of the perovskite-type compound YRh3B revealing a Rh deficiency

R. Makita, K. Tanizawa, K. Tanaka and H. Takei

Abstract top

In contrast with previous structural studies of ytterbium trirhodium boride, YbRh3B, that suggest a boron deficiency, the current redetermination of the crystal structure of YbRh3B revealed instead a rhodium deficiency with a refined composition of YbRh2.67 (2)B. In the ABX3 perovskite-type structure, Yb, B and Rh are located on the A, B and X positions, respectively, with site symmetries of m\overline{3}m for the A and B sites, and 4/mm.m for the X site.

Comment top

Takei & Shishido (1984) reported various rare earth trirhodium borides with the perovskite structure (Fig. 1) and suggest a deficiency for the boron site. For a closer inspection of this assumption and since anisotropic displacement factors were not reported in the original study, we decided to re-determine the structure of YbRh3B and present the results of the structure analysis in this communication.

In the ABX3 perovskite-type structure, Yb, B and the partly occupied Rh atoms are located on the A, B and X positions, respectively, with site symmetries of m3m for the A and B sites and 4/mm.m for the X site.

Related literature top

For a previous powder diffraction study of YbRh3B, see: Takei & Shishido (1984). For general background, see: Becker & Coppens (1975); Libermann et al. (1971); Mann (1968).

Experimental top

Single crystals were grown using a flux method with copper as the solvent. Stoichiometric quantities of Yb, Rh and B were mixed with copper in a ratio of about 1:8 by weight. The mixture was heated in a high purity alumina crucible by electric furnace under a purified He gas flow at a rate of about 400 Kh-1. The sample was kept at a temperature between 1523 and 1623 K for 10 h and cooled at a rate of 1 Kh-1 to 353 K. Then the furnace was cooled rapidly to room temperature. The boride crystals were separated from the copper by treatment with hot nitric acid. The sample was cut into small pieces and was finally ground into a sphere with 41 µm radius by a wind pressure granulation machine with diamond paste.

Refinement top

In the first stage of the refinement the site occupation factors (s.o.f.) of Yb, Rh and B were assumed to be 1. Fig. 2 (a), (b) and (c) show the difference density map at this stage of the refinement around Yb, Rh and B, respectively. The center of the difference density map is the core of atom; the width and depth of the difference density map is 4.13 Å × 4.13 Å. The (ρmax, ρmin) values for Yb, Rh and B were (-4.59, 8.48), (-4.92, 9.06) and (-4.91, 8.58) eÅ-3, respectively, with the R-factor converging at 3.14%. After this stage we checked the results of Takei & Shishido (1984) for a deficiency of the boron site and refined the s.o.f. of boron. However, the R-factor and the difference density map showed no noticeable improvement. Then the s.o.f. of both Yb and Rh were refined independently. Whereas the s.o.f. of Yb remained unchanged, that of Rh changed from 1 to 0.891 (6). Fig. 3 (a), (b) and (c) show the difference density map around Yb, Rh and B after the refinement of the s.o.f. of Rh. The positive and negative peaks showed a significant improvement compared with the first refinement with a constrained s.o.f. for Rh. The remaining electron densities (ρmax, ρmin) around Yb, Rh and B were (-1.89, 1.79), (-1.96, 1.86) and (-1.98, 1.33) eÅ-3, respectively, and the R-factor converged at 1.4%.

Computing details top

Data collection: MXCSYS (MacScience, 1995) and IUANGLE (Tanaka et al., 1994).; cell refinement: RSLC-3 UNICS system (Sakurai & Kobayashi, 1979); data reduction: RDEDIT (Tanaka, 2008); program(s) used to solve structure: QNTAO (Tanaka & Ōnuki, 2002; Tanaka et al., 2008); program(s) used to refine structure: QNTAO (Tanaka & Ōnuki, 2002; Tanaka et al., 2008); molecular graphics: ATOMS for Windows (Dowty, 2000); software used to prepare material for publication: RDEDIT (Tanaka, 2008).

Figures top
[Figure 1] Fig. 1. The structure of YbRh3B with displacement ellipsoids drawn at the 90% probability level.
[Figure 2] Fig. 2. The difference density map around (a) Yb at (1/2, 1/2, 1/2) on the (002) plane with a range of 0 < x < 1 and 0 < y < 1, (b) around Rh at (1/2, 1/2, 1/2) on the (002) plane with a range of -0.5 < x < 0.5 and -0.5 < y < 0.5 and (c) around B at (1/2, 1/2, 0) on the (001) plane with a range of -0.5 < x < 0.5 and -0.5 < y < 0.5. For all atoms full occupancy is considered. Contour lines are at intervals of 0.5 e Å-3. Zero contours are drawn as thick lines, positive contours are drawn as thin lines, negative contours are drawn as broken lines.
[Figure 3] Fig. 3. The difference density map around (a) Yb, (b) Rh and (c) B after the refinement of the site occupation factors for the Rh site. Contour lines are as in Fig. 2.
Ytterbium trirhodium boride top
Crystal data top
YbRh2.67BDx = 10.81 Mg m−3
Mr = 458.61Mo Kα radiation, λ = 0.71073 Å
Cubic, Pm3mCell parameters from 30 reflections
Hall symbol: -P 4 2 3θ = 36.5–38.3°
a = 4.12992 (7) ŵ = 47.90 mm−1
V = 70.44 (1) Å3T = 109 K
Z = 1Sphere, black
F(000) = 195.140.08 × 0.08 × 0.08 × 0.04 (radius) mm
Data collection top
MacScience M06XHF22 four-circle
diffractometer		193 independent reflections
Radiation source: fine-focus rotating anode193 reflections with F > 3σ(F)
graphiteRint = 0.019
Detector resolution: 1.25 x 1.25° pixels mm-1θmax = 74.9°, θmin = 4.9°
ω/2θ scansh = −7→9
Absorption correction: for a sphere
[transmission coefficients for spheres tabulated in International Tables for X-ray Crystallography (Vol. II, 1972, Table 5.3.6B) were interpolated with Lagrange's method (four point interpolation; Yamauchi et al., 1965)]		k = −11→11
Tmin = 0.069, Tmax = 0.169l = −11→11
953 measured reflections
Refinement top
Refinement on F3 restraints
Least-squares matrix: fullWeighting scheme based on measured s.u.'s
R[F2 > 2σ(F2)] = 0.014(Δ/σ)max = 0.0001
wR(F2) = 0.029Δρmax = 1.86 e Å−3
S = 1.15Δρmin = −1.98 e Å−3
193 reflectionsExtinction correction: B-C type 1 Gaussian anisotropic (Becker & Coppens, 1975)
11 parametersExtinction coefficient: 0.052 (2) times 104
Crystal data top
YbRh2.67BZ = 1
Mr = 458.61Mo Kα radiation
Cubic, Pm3mµ = 47.90 mm−1
a = 4.12992 (7) ÅT = 109 K
V = 70.44 (1) Å30.08 × 0.08 × 0.08 × 0.04 (radius) mm
Data collection top
MacScience M06XHF22 four-circle
diffractometer		193 independent reflections
Absorption correction: for a sphere
[transmission coefficients for spheres tabulated in International Tables for X-ray Crystallography (Vol. II, 1972, Table 5.3.6B) were interpolated with Lagrange's method (four point interpolation; Yamauchi et al., 1965)]		193 reflections with F > 3σ(F)
Tmin = 0.069, Tmax = 0.169Rint = 0.019
953 measured reflectionsθmax = 74.9°
Refinement top
R[F2 > 2σ(F2)] = 0.014Δρmax = 1.86 e Å−3
wR(F2) = 0.029Δρmin = −1.98 e Å−3
S = 1.15Absolute structure: ?
193 reflectionsFlack parameter: ?
11 parametersRogers parameter: ?
3 restraints
Special details top

Experimental. Multiple diffraction was avoided by using ψ-scans. Intensities was measured at the equi-temperature region of combinaion of angles ω and χ of a four-circle diffractometer.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Yb0.50000.50000.50000.212 (1)
Rh0.00000.00000.50000.143 (2)0.891 (6)
B0.00000.00000.00000.291 (6)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Yb0.00269 (4)0.00269 (4)0.00269 (4)000
Rh0.00202 (6)0.00202 (6)0.00139 (6)000
B0.0037 (2)0.0037 (2)0.0037 (2)000
Geometric parameters (Å, °) top
Rhi—Rhii2.92029 (7)Bi—Yb3.57662 (7)
Bi—Rhi2.06496 (7)Rhi—Yb2.92029 (7)
?···??
Rhi—Bi—Rhii90.000Rhi—Yb—Bi35.264
Rhi—Yb—Rhii60.000Yb—Bi—Rhii54.736
Symmetry codes: (i) x+1, y, z; (ii) z, x, y.
Table 1
Selected geometric parameters (Å) top
Rhi—Rhii2.92029 (7)Bi—Yb3.57662 (7)
Bi—Rhi2.06496 (7)Rhi—Yb2.92029 (7)
Symmetry codes: (i) x+1, y, z; (ii) z, x, y.
references
References top

Becker, P. J. & Coppens, P. (1975). Acta Cryst. A31, 417–425.

Dowty, E. (2000). ATOMS for Windows. Shape Software, Kingsport, Tennessee, USA.

Libermann, D. A., Cromer, D. T. & Waber, J. T. (1971). Comput. Phys. Commun. 2, 107–113.

MacScience (1995). MXCSYS. Bruker AXS, Tsukuba, Ibaraki, Japan.

Mann, J. B. (1968). Los Alamos Scientific Report No. LA3691. Los Alamos National Laboratory, Los Alamos, New Mexico, USA.

Sakurai, T. & Kobayashi, K. (1979). Rep. Inst. Phys. Chem. Res. 55, 69–77. [Journal title not known. Should it be Rep. Inst. Chem. Res. Kyoto Univ. ?]

Takei, H. & Shishido, T. (1984). J. Less Comm. Met. 97, 223–229.

Tanaka, K. (2008). RDEDIT. Unpublished.

Tanaka, K., Kumazawa, S., Tsubokawa, M., Maruno, S. & Shirotani, I. (1994). Acta Cryst. A50, 246–252.

Tanaka, K., Makita, R., Funahashi, S., Komori, T. & Zaw Win, (2008). Acta Cryst. A64, 437–449.

Tanaka, K. & Ōnuki, Y. (2002). Acta Cryst. B58, 423–436.

Yamauchi, J., Moriguchi, S. & Ichimatsu, S. (1965). Numerical Calculation Method for Computer. Tokyo: Baifūkan.