inorganic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

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Boron carbide, B13-xC2-y (x = 0.12, y = 0.01)

aNational Institute for Materials Science, Namiki 1-1, 305-0044 Tsukuba, Japan
*Correspondence e-mail: MORI.Takao@nims.go.jp

(Received 10 July 2012; accepted 21 July 2012; online 28 July 2012)

Boron carbide phases exist over a widely varying compos­itional range B12+xC3-x (0.06 < x < 1.7). One idealized structure corresponds to the B13C2 composition (space group R-3m) and contains one icosa­hedral B12 unit and one linear C—B—C chain. The B12 units are composed of crystallographically distinct B atoms BP (polar, B1) and BEq (equatorial, B2). Boron icosa­hedra are inter­connected by C atoms via their BEq atoms, forming layers parallel to (001), while the B12 units of the adjacent layers are linked through inter­icosa­hedral BP—BP bonds. The unique B atom (BC) connects the two C atoms of adjacent layers, forming a C—B—C chain along [001]. Depending on the carbon concentration, the carbon and BP sites exhibit mixed B/C occupancies to varying degrees; besides, the BC site shows partial occupancy. The decrease in carbon content was reported to be realized via an increasing number of chainless unit cells. On the basis of X-ray single-crystal refinement, we have concluded that the unit cell of the given boron-rich crystal contains following structural units: [B12] and [B11C] icosa­hedra (about 96 and 4%, respectively) and C—B—C chains (87%). Besides, there is a fraction of unit cells (13%) with the B atom located against the triangular face of a neighboring icosa­hedron formed by BEq (B2) thus rendering the formula B0.87(B0.98C0.02)12(B0.13C0.87)2 for the current boron carbide crystal.

Related literature

For X-ray/neutron diffraction studies on boron carbide, see: Yakel (1975[Yakel, H. L. (1975). Acta Cryst. B31, 1797-1806.]); Will et al. (1979[Will, G., Kirfel, A., Gupta, A. & Amberger, E. (1979). J. Less Common Met. 67, 19-29.]); Larson (1986[Larson, A. C. (1986). AIP Conf. Proc. 140, 109-113.]); Kwei & Morosin (1996[Kwei, G. H. & Morosin, B. (1996). J. Phys. Chem. 100, 8031-8039.]). For the boron carbide homogeneity field, see: Bouchacourt & Thevenot (1985[Bouchacourt, M. & Thevenot, F. (1985). J. Mater. Sci. 20, 1237-1247.]); Gosset & Colin (1991[Gosset, D. & Colin, M. (1991). J. Nucl. Mater. 183, 161-173.]). For electronic structure and bonding properties, see: Domnich et al. (2011[Domnich, V., Reynaud, S., Haber, R. A. & Chhowalla, M. (2011). J. Am. Ceram. Soc. 94, 3605-3628.]); Balakrishnarajan et al. (2007[Balakrishnarajan, M. M., Pancharatna, P. D. & Hoffmann, R. (2007). New J. Chem. 31, 473-485.]). For electronic properties and charge transport, see: Werheit (2009[Werheit, H. (2009). J. Phys. Conf. Ser. 176, 012019.]).

Experimental

Crystal data
  • C1.99B12.88

  • Mr = 163.14

  • Trigonal, [R \overline 3m ]

  • a = 5.6530 (8) Å

  • c = 12.156 (4) Å

  • V = 336.42 (17) Å3

  • Z = 3

  • Mo Kα radiation

  • μ = 0.10 mm−1

  • T = 293 K

  • 0.45 × 0.30 × 0.21 mm

Data collection
  • Rigaku AFC 7R diffractometer

  • 1489 measured reflections

  • 284 independent reflections

  • 184 reflections with I > 2σ(I)

  • Rint = 0.151

  • 3 standard reflections every 150 reflections intensity decay: none

Refinement
  • R[F2 > 2σ(F2)] = 0.046

  • wR(F2) = 0.109

  • S = 1.03

  • 284 reflections

  • 22 parameters

  • 1 restraint

  • Δρmax = 0.55 e Å−3

  • Δρmin = −0.37 e Å−3

Data collection: Rigaku/AFC Diffractometer Control Software (Rigaku, 1998[Rigaku (1998). Rigaku/AFC Diffractometer Control Software. Rigaku Corporation, Akishima, Tokyo, Japan.]); cell refinement: Rigaku/AFC Diffractometer Control Software; data reduction: TEXSAN (Molecular Structure Corporation, 1998[Molecular Structure Corporation (1998). TEXSAN. MSC, The Woodlands, Texas, USA.]); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: ATOMS (Dowty, 1999[Dowty, E. (1999). ATOMS. Shape Software, Kingsport, Tennessee, USA.]); software used to prepare material for publication: SHELXL97 and WinGX (Farrugia, 1999[Farrugia, L. J. (1999). J. Appl. Cryst. 32, 837-838.]).

Supporting information


Comment top

The positioning the C1 and B11 atoms on two adjacent 6c (0, 0, z) sites is in good agreement with observations reported from powder neutron diffraction studies of boron-rich boron carbides by Kwei and Morosin (1996). No atom in the 36i site claimed by Yakel (1975) has been found.

Related literature top

For X-ray/neutron diffraction studies on boron carbide, see: Yakel (1975); Will et al. (1979); Larson (1986); Kwei & Morosin (1996). For boron carbide homogeneity field, see: Bouchacourt & Thevenot (1985); Gosset & Colin (1991). For electronic structure and bonding properties, see: Domnich et al. (2011); Balakrishnarajan et al. (2007). For electronic properties and charge transport, see: Werheit (2009).

Experimental top

Boron carbide single-crystal has been obtained as a co-product of the yttrium boron carbide phase synthesized via solid state reaction of yttrium tetraboride, amorphous boron and carbon. The reaction process was performed from compacted powders in the BN crucible inserted into a graphite susceptor using the RF furnace under a flow of Ar at a temperature of about 1973 K and holding time 8 h; afterwards the setup was cooled down in 1 h to room temperature. The sample contained crystals of the title compound, in the presence of YB28.5C4 and binary yttrium borides, as revealed by powder X-ray diffraction analysis.

Refinement top

The crystal structure refinement was performed starting from the atomic coordinates reported for α-rh B. The chain atoms were located from the difference Fourier synthesis. The refinement on boron icosahedral polar site-occupancy factors led to reliability factors R1=0.0517 and wR2=0.1519 revealing the remaining electron density of 1.42 e Å-3 in 6c Wyckoff position (0, 0, z; z=0.07) at close distance from chain atom C1. Further refinement on occupancy parameters of the B3 (BC) chain atom and refining the C1/B11 in split 6c atom site reduced the highest Fourier difference peak to 0.55 e Å-3 at (0, 0, 0.1663) located 0.6 Å away from C1 and decreased the reliability factors to R1=0.0455 and wR2=0.1087. The ADPs of B1 and B2 have comparable values, while the thermal ellipsoids of C1/B11 chain atoms slightly extend parallel to the chain direction. The B3 in the center of a chain shows rather large ADP values. Data collection and cell refinement:

Structure description top

The positioning the C1 and B11 atoms on two adjacent 6c (0, 0, z) sites is in good agreement with observations reported from powder neutron diffraction studies of boron-rich boron carbides by Kwei and Morosin (1996). No atom in the 36i site claimed by Yakel (1975) has been found.

For X-ray/neutron diffraction studies on boron carbide, see: Yakel (1975); Will et al. (1979); Larson (1986); Kwei & Morosin (1996). For boron carbide homogeneity field, see: Bouchacourt & Thevenot (1985); Gosset & Colin (1991). For electronic structure and bonding properties, see: Domnich et al. (2011); Balakrishnarajan et al. (2007). For electronic properties and charge transport, see: Werheit (2009).

Computing details top

Data collection: Rigaku/AFC Diffractometer Control Software (Rigaku, 1998); cell refinement: Rigaku/AFC Diffractometer Control Software (Rigaku, 1998); data reduction: TEXSAN (Molecular Structure Corporation, 1998); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ATOMS (Dowty, 1999); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and WinGX (Farrugia, 1999).

Figures top
[Figure 1] Fig. 1. The idealized structure of boron carbide and the distances for B and C atoms of the C—B—C and B—B chains as obtained from structure refinement. Thermal ellipsoids depict the 80% probability level.
[Figure 2] Fig. 2. Observed Fourier maps projected onto xy plane at z=0; -1.5 e Å-3 < Δρ < 28.4 e Å-3.
Boron carbide top
Crystal data top
C1.99B12.88Dx = 2.416 Mg m3
Mr = 163.14Mo Kα radiation, λ = 0.71073 Å
Trigonal, R3mCell parameters from 20 reflections
Hall symbol: -R 3 2"θ = 8–50°
a = 5.6530 (8) ŵ = 0.10 mm1
c = 12.156 (4) ÅT = 293 K
V = 336.42 (17) Å3Prism, black
Z = 30.45 × 0.3 × 0.21 mm
F(000) = 229
Data collection top
Rigaku AFC 7R
diffractometer
θmax = 39.8°, θmin = 4.5°
ω–2θ scansh = 108
1489 measured reflectionsk = 010
284 independent reflectionsl = 2121
184 reflections with I > 2σ(I)3 standard reflections every 150 reflections
Rint = 0.151 intensity decay: none
Refinement top
Refinement on F222 parameters
Least-squares matrix: full1 restraint
R[F2 > 2σ(F2)] = 0.046 w = 1/[σ2(Fo2) + (0.0481P)2 + 0.3407P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.109(Δ/σ)max = 0.002
S = 1.03Δρmax = 0.55 e Å3
284 reflectionsΔρmin = 0.37 e Å3
Crystal data top
C1.99B12.88Z = 3
Mr = 163.14Mo Kα radiation
Trigonal, R3mµ = 0.10 mm1
a = 5.6530 (8) ÅT = 293 K
c = 12.156 (4) Å0.45 × 0.3 × 0.21 mm
V = 336.42 (17) Å3
Data collection top
Rigaku AFC 7R
diffractometer
Rint = 0.151
1489 measured reflections3 standard reflections every 150 reflections
284 independent reflections intensity decay: none
184 reflections with I > 2σ(I)
Refinement top
R[F2 > 2σ(F2)] = 0.04622 parameters
wR(F2) = 0.1091 restraint
S = 1.03Δρmax = 0.55 e Å3
284 reflectionsΔρmin = 0.37 e Å3
Special details top

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 (Å2) top
xyzUiso*/UeqOcc. (<1)
B10.44092 (16)0.55908 (16)0.05298 (12)0.0053 (3)0.958 (4)
C110.44092 (16)0.55908 (16)0.05298 (12)0.0053 (3)0.042 (4)
B20.50336 (16)0.49664 (16)0.19232 (11)0.0054 (3)
B30000.0118 (8)0.87
C1000.1177 (5)0.0071 (8)0.87 (2)
B11000.079 (4)0.0071 (8)0.13 (2)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
B10.0056 (4)0.0056 (4)0.0047 (5)0.0028 (5)0.0001 (2)0.0001 (2)
C110.0056 (4)0.0056 (4)0.0047 (5)0.0028 (5)0.0001 (2)0.0001 (2)
B20.0046 (4)0.0046 (4)0.0059 (5)0.0015 (4)0.0003 (2)0.0003 (2)
B30.0099 (11)0.0099 (11)0.016 (2)0.0049 (6)00
C10.0041 (6)0.0041 (6)0.013 (2)0.0021 (3)00
B110.0041 (6)0.0041 (6)0.013 (2)0.0021 (3)00
Geometric parameters (Å, º) top
B1—C11i1.731 (3)B2—B1ii1.8091 (15)
B1—B1i1.731 (3)B2—C11iii1.8091 (15)
B1—B21.801 (2)B2—B1iii1.8091 (15)
B1—B2ii1.8091 (15)B3—B110.96 (5)
B1—B2iii1.8091 (15)B3—B11vii0.96 (5)
B1—B1iv1.825 (3)B3—C1vii1.430 (6)
B1—C11iv1.825 (3)B3—C11.430 (6)
B1—C11v1.825 (3)C1—B2vi1.6239 (19)
B1—B1v1.825 (3)C1—B2iii1.6239 (19)
B2—C1vi1.6239 (19)C1—B2viii1.6239 (19)
B2—B11vi1.77 (2)B11—B2vi1.77 (2)
B2—B2iii1.7778 (17)B11—B2iii1.77 (2)
B2—B2ii1.7778 (17)B11—B2viii1.77 (2)
B2—C11ii1.8091 (15)B11—B11vii1.92 (9)
C11i—B1—B1i0.00 (8)B11vi—B2—C11ii108.5 (11)
C11i—B1—B2118.22 (14)B2iii—B2—C11ii108.78 (7)
B1i—B1—B2118.22 (14)B2ii—B2—C11ii60.26 (7)
C11i—B1—B2ii121.45 (8)B1—B2—C11ii110.05 (9)
B1i—B1—B2ii121.45 (8)C1vi—B2—B1ii121.07 (19)
B2—B1—B2ii59.01 (5)B11vi—B2—B1ii108.5 (11)
C11i—B1—B2iii121.45 (8)B2iii—B2—B1ii108.78 (7)
B1i—B1—B2iii121.45 (8)B2ii—B2—B1ii60.26 (7)
B2—B1—B2iii59.01 (5)B1—B2—B1ii110.05 (9)
B2ii—B1—B2iii105.68 (11)C11ii—B2—B1ii0.00 (11)
C11i—B1—B1iv125.36 (8)C1vi—B2—C11iii121.07 (19)
B1i—B1—B1iv125.36 (8)B11vi—B2—C11iii108.5 (11)
B2—B1—B1iv107.10 (6)B2iii—B2—C11iii60.26 (7)
B2ii—B1—B1iv107.02 (6)B2ii—B2—C11iii108.78 (7)
B2iii—B1—B1iv59.72 (5)B1—B2—C11iii110.05 (9)
C11i—B1—C11iv125.36 (8)C11ii—B2—C11iii60.56 (11)
B1i—B1—C11iv125.36 (8)B1ii—B2—C11iii60.56 (11)
B2—B1—C11iv107.10 (6)C1vi—B2—B1iii121.07 (19)
B2ii—B1—C11iv107.02 (6)B11vi—B2—B1iii108.5 (11)
B2iii—B1—C11iv59.72 (5)B2iii—B2—B1iii60.26 (7)
B1iv—B1—C11iv0.00 (9)B2ii—B2—B1iii108.78 (7)
C11i—B1—C11v125.36 (8)B1—B2—B1iii110.05 (9)
B1i—B1—C11v125.36 (8)C11ii—B2—B1iii60.56 (11)
B2—B1—C11v107.10 (6)B1ii—B2—B1iii60.56 (11)
B2ii—B1—C11v59.72 (5)C11iii—B2—B1iii0.00 (4)
B2iii—B1—C11v107.02 (6)B11—B3—B11vii180.0000 (10)
B1iv—B1—C11v60B11—B3—C1vii180.0000 (10)
C11iv—B1—C11v60B11vii—B3—C1vii0.0000 (10)
C11i—B1—B1v125.36 (8)B11—B3—C10.0000 (10)
B1i—B1—B1v125.36 (8)B11vii—B3—C1180.0000 (10)
B2—B1—B1v107.10 (6)C1vii—B3—C1180
B2ii—B1—B1v59.72 (5)B3—C1—B2vi100.1 (2)
B2iii—B1—B1v107.02 (6)B3—C1—B2iii100.1 (2)
B1iv—B1—B1v60B2vi—C1—B2iii117.01 (13)
C11iv—B1—B1v60B3—C1—B2viii100.1 (2)
C11v—B1—B1v0.00 (10)B2vi—C1—B2viii117.01 (13)
C1vi—B2—B11vi15.1 (12)B2iii—C1—B2viii117.01 (13)
C1vi—B2—B2iii121.49 (7)B3—B11—B2vi115.2 (13)
B11vi—B2—B2iii125.0 (2)B3—B11—B2iii115.2 (13)
C1vi—B2—B2ii121.49 (7)B2vi—B11—B2iii103.2 (16)
B11vi—B2—B2ii125.0 (2)B3—B11—B2viii115.2 (13)
B2iii—B2—B2ii108.39 (8)B2vi—B11—B2viii103.2 (16)
C1vi—B2—B1119.9 (2)B2iii—B11—B2viii103.2 (16)
B11vi—B2—B1135.0 (14)B3—B11—B11vii0.0000 (10)
B2iii—B2—B160.73 (7)B2vi—B11—B11vii115.2 (13)
B2ii—B2—B160.73 (7)B2iii—B11—B11vii115.2 (13)
C1vi—B2—C11ii121.07 (19)B2viii—B11—B11vii115.2 (13)
Symmetry codes: (i) x+1, y+1, z; (ii) xy+2/3, x+1/3, z+1/3; (iii) y1/3, x+y+1/3, z+1/3; (iv) x+y, x+1, z; (v) y+1, xy+1, z; (vi) x+2/3, y+1/3, z+1/3; (vii) x, y, z; (viii) xy1/3, x2/3, z+1/3.

Experimental details

Crystal data
Chemical formulaC1.99B12.88
Mr163.14
Crystal system, space groupTrigonal, R3m
Temperature (K)293
a, c (Å)5.6530 (8), 12.156 (4)
V3)336.42 (17)
Z3
Radiation typeMo Kα
µ (mm1)0.10
Crystal size (mm)0.45 × 0.3 × 0.21
Data collection
DiffractometerRigaku AFC 7R
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
1489, 284, 184
Rint0.151
(sin θ/λ)max1)0.901
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.046, 0.109, 1.03
No. of reflections284
No. of parameters22
No. of restraints1
Δρmax, Δρmin (e Å3)0.55, 0.37

Computer programs: Rigaku/AFC Diffractometer Control Software (Rigaku, 1998), TEXSAN (Molecular Structure Corporation, 1998), SHELXS97 (Sheldrick, 2008), ATOMS (Dowty, 1999), SHELXL97 (Sheldrick, 2008) and WinGX (Farrugia, 1999).

 

Acknowledgements

This work was partly supported by grants from the Thermal and Electric Energy Technology Foundation and AOARD.

References

First citationBalakrishnarajan, M. M., Pancharatna, P. D. & Hoffmann, R. (2007). New J. Chem. 31, 473–485.  Web of Science CrossRef CAS Google Scholar
First citationBouchacourt, M. & Thevenot, F. (1985). J. Mater. Sci. 20, 1237–1247.  CrossRef CAS Web of Science Google Scholar
First citationDomnich, V., Reynaud, S., Haber, R. A. & Chhowalla, M. (2011). J. Am. Ceram. Soc. 94, 3605–3628.  Web of Science CrossRef CAS Google Scholar
First citationDowty, E. (1999). ATOMS. Shape Software, Kingsport, Tennessee, USA.  Google Scholar
First citationFarrugia, L. J. (1999). J. Appl. Cryst. 32, 837–838.  CrossRef CAS IUCr Journals Google Scholar
First citationGosset, D. & Colin, M. (1991). J. Nucl. Mater. 183, 161–173.  CrossRef CAS Web of Science Google Scholar
First citationKwei, G. H. & Morosin, B. (1996). J. Phys. Chem. 100, 8031–8039.  CrossRef CAS Web of Science Google Scholar
First citationLarson, A. C. (1986). AIP Conf. Proc. 140, 109–113.  CrossRef CAS Google Scholar
First citationMolecular Structure Corporation (1998). TEXSAN. MSC, The Woodlands, Texas, USA.  Google Scholar
First citationRigaku (1998). Rigaku/AFC Diffractometer Control Software. Rigaku Corporation, Akishima, Tokyo, Japan.  Google Scholar
First citationSheldrick, G. M. (2008). Acta Cryst. A64, 112–122.  Web of Science CrossRef CAS IUCr Journals Google Scholar
First citationWerheit, H. (2009). J. Phys. Conf. Ser. 176, 012019.  CrossRef Google Scholar
First citationWill, G., Kirfel, A., Gupta, A. & Amberger, E. (1979). J. Less Common Met. 67, 19–29.  CrossRef CAS Web of Science Google Scholar
First citationYakel, H. L. (1975). Acta Cryst. B31, 1797–1806.  CrossRef CAS IUCr Journals Web of Science Google Scholar

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