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Ga4B2O9, an aluminium-free mullite-type compound, was prepared by a boric-acid flux method and its structure was determined using powder X-ray diffraction techniques, in combination with transmission electron microscopy, solid-state 11B MAS-NMR and IR spectroscopies. GaO6 octahedra share edges in a trans-manner forming one-dimensional chains along the b direction, and the chains are further cross-linked by GaO5, BO3 and BO4 groups into a three-dimensional mullite-type structure. The disorder of the inter-chain groups results in a small unit cell for Ga4B2O9 compared with that for Al4B2O9, an ordered compound with a superstructure. By deconstructing the structure of Ga4B2O9, we were able to identify the fundamental building units and their linking rules which can be used to reconstruct the ordered and disordered structures. For Ga4B2O9, we found that the structure is intrinsically disordered within the ac plane, but ordered along the b axis. The three-dimensional structure can then be constructed by stacking the disordered ac sheets along the b axis (½b) with a ½a shift. The fundamental building units and exclusivity rules identified in this gallium borate mullite may also be useful for understanding other related mullite phases. The structure analysis applying the proposed method is used to recognize the structural features of Al4B2O9 and Al18B4O33.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768110000650/kd5038sup1.cif
Contains datablocks global, znvoprofile

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0108768110000650/kd5038znvoprofilesup2.rtv
Contains datablock znvoprofile

pdf

Portable Document Format (PDF) file https://doi.org/10.1107/S0108768110000650/kd5038sup3.pdf
SEM image, X-ray diffraction patterns and Rietveld plot

Computing details top

(znvoprofile) top
Crystal data top
B2Ga4O9Z = 4
Mr = 444.50F(000) = 824.0
Monoclinic, C2/mDx = 4.337 Mg m3
a = 15.3658 (2) ÅCu Kα radiation, λ = 1.540596 Å
b = 5.72177 (5) ÅT = 293 K
c = 10.9987 (1) Åwhite
β = 135.2372 (7)°Specimen preparation: Prepared at 488 K
V = 680.94 (2) Å3
Data collection top
Bruker Advance 8
diffractometer
Data collection mode: transmission
Radiation source: sealed X-ray tubeScan method: step
Ge monochromator2θmin = 8°, 2θmax = 119.988°, 2θstep = 0.014°
Specimen mounting: capillary (0.3 mm)
Refinement top
Rp = 0.0644 constraints
Rwp = 0.086Primary atom site location: structure-invariant direct methods
Rexp = 0.013Secondary atom site location: inferred from neighbouring sites
7779 data pointsWeighting scheme based on measured s.u.'s 1/[Yi]
Profile function: Pseudo-Voigt(Δ/σ)max = 0.01
46 parametersBackground function: 6 Legendre polynoms
0 restraints
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Ga10.250.2500.0095 (1)
Ga20.250.250.50.0095 (1)
Ga30.4797 (2)0.50.3194 (3)0.0175 (1)
Ga40.2884 (4)0.50.3085 (6)0.0171 (1).5
Ga50.1411 (4)0.50.1388 (6)0.0171 (1).5
B10.215 (2)00.207 (3)0.019 (2)
B210.004 (5)0.50.284 (7)0.019 (2).5
B220.001 (6)0.50.234 (7)0.019 (2).5
O10.1559 (8)00.450 (1)0.0095 (2)
O20.269 (1)0.50.128 (1)0.0095 (2)
O30.125 (9)0.50.393 (1)0.0095 (2)
O40.2212 (9)00.095 (1)0.0095 (2)
O50.4321 (5)0.206 (1)0.2071 (7)0.0095 (2)
O60.2114 (6)0.200 (1)0.2779 (8)0.0095 (2)
O70.454 (2)0.50.454 (3)0.013 (1).5
O80.008 (2)0.50.094 (3)0.013 (1).5
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
???????
Geometric parameters (Å, º) top
Ga1—O21.879 (8)Ga4—O61.975 (8)
Ga1—O42.01 (1)Ga4—O71.80 (2)
Ga1—O52.008 (5)Ga5—O22.05 (2)
Ga2—O11.820 (8)Ga5—O62.028 (6)
Ga2—O31.98 (7)Ga5—O81.82 (2)
Ga2—O62.08 (1)B1—O41.29 (4)
Ga3—O22.29 (1)B1—O61.40 (2)
Ga3—O51.897 (6)B21—O31.32 (6)
Ga3—O71.78 (4)B22—O31.410 (9)
Ga4—O21.79 (2)
O2—Ga1—O584.0O5—Ga3—O7109.3
O2—Ga1—O497.4O2—Ga4—O6101.6
O4—Ga1—O588.0O2—Ga4—O790.1
O1—Ga2—O691.9O6—Ga4—O7116.6
O1—Ga2—O399.4O2—Ga5—O691.4
O3—Ga2—O693.0O2—Ga5—O894.8
O2—Ga3—O776.3O6—Ga5—O8121.8
O2—Ga3—O576.2O4—B1—O6125.4
 

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