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The crystal structure of the low-temperature form of barium metagermanate (BaGeO3) has been determined from laboratory X-ray powder diffraction data collected at 298.5 (5) K. The structure was found to consist of alternating layers of Ba cations and [GeO3]3 rings, and is closely related to pseudo-wollastonite. The rings show a twofold positional disorder owing to stacking faults. The stacking is not random, but can be rationalized by a twinning mechanism mapping the two non-congruent enantiomorphic polytypes of the structure onto each other. This model also explains the diffuse scattering and twinning observed in SAED and HRTEM, as well as the size and strain-like broadening effects found in the XRPD pattern.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768106039140/ws5051sup1.cif
Contains datablocks global, BaGeO3, BaGeO3-TM

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0108768106039140/ws5051sup2.rtv
Contains datablock BaGeO3

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108768106039140/ws5051sup3.hkl
Contains datablock BaGeO3

Computing details top

Data collection: STOE WinXPow; program(s) used to solve structure: intuitive; program(s) used to refine structure: FULLPROF.

Figures top
[Figure 1]
[Figure 2]
[Figure 3]
[Figure 4]
[Figure 5]
(BaGeO3) top
Crystal data top
Ge3O9·3(Ba)V = 1089.76 (2) Å3
Mr = 257.94Z = 12
Monoclinic, C2/c? radiation, λ = 1.540560 Å
Hall symbol: -C 2ycµ = 5.8 mm1
a = 13.18949 (15) ÅT = 299 K
b = 7.62045 (5) Åwhite
c = 11.71698 (9) Åflat_sheet, 8 × 8 mm
β = 112.2783 (7)°Specimen preparation: Prepared at 1323 K
Data collection top
STOE STADI MP
diffractometer
Absorption correction: empirical (using intensity measurements) from beam loss
?
Radiation source: X-ray tubeTmin = ?, Tmax = ?
Asymmetric Ge(111) monochromator2θmin = 2.053°, 2θmax = 129.983°, 2θstep = 0.010°
Data collection mode: transmission
Refinement top
Rp = 3.30312794 data points
Rwp = 4.26862 parameters
Rexp = 3.15912 restraints
RBragg = 4.542
χ2 = 3.349
Crystal data top
Ge3O9·3(Ba)V = 1089.76 (2) Å3
Mr = 257.94Z = 12
Monoclinic, C2/c? radiation, λ = 1.540560 Å
a = 13.18949 (15) ŵ = 5.8 mm1
b = 7.62045 (5) ÅT = 299 K
c = 11.71698 (9) Åflat_sheet, 8 × 8 mm
β = 112.2783 (7)°
Data collection top
STOE STADI MP
diffractometer
Tmin = ?, Tmax = ?
Data collection mode: transmission2θmin = 2.053°, 2θmax = 129.983°, 2θstep = 0.010°
Absorption correction: empirical (using intensity measurements) from beam loss
?
Refinement top
Rp = 3.303χ2 = 3.349
Rwp = 4.26812794 data points
Rexp = 3.15962 parameters
RBragg = 4.54212 restraints
Special details top

Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Ba10.0838 (3)0.2521 (4)0.5001 (6)0.0093 (2)*
Ba20.250000.250000.000000.0093 (2)*
Ge10.6592 (5)0.8371 (7)0.2505 (5)0.0093 (2)*0.50000
Ge20.7953 (5)0.4653 (8)0.2508 (5)0.0093 (2)*0.50000
Ge30.5429 (4)0.4497 (7)0.2508 (5)0.0093 (2)*0.50000
O10.5593 (15)0.6811 (11)0.249 (3)0.0093 (2)*0.50000
O20.7634 (16)0.6927 (12)0.247 (3)0.0093 (2)*0.50000
O30.670 (2)0.3739 (17)0.251 (6)0.0093 (2)*0.50000
O40.6051 (13)0.934 (2)0.1082 (7)0.0093 (2)*
O50.6999 (16)0.937 (2)0.3920 (7)0.0093 (2)*
O60.4572 (12)0.404 (3)0.1055 (7)0.0093 (2)*
Geometric parameters (Å, º) top
Ge1—O11.7685Ge2—O4i1.6936
Ge1—O21.7734Ge2—O5i1.7118
Ge1—O41.7110Ge3—O11.7778
Ge1—O51.7166Ge3—O31.7714
Ge2—O21.7800Ge3—O61.6849
Ge2—O31.7950Ge3—O6ii1.7197
O1—Ge1—O299.38O1—Ge3—O3101.76
O1—Ge1—O4104.10O1—Ge3—O6103.22
O1—Ge1—O5105.66O1—Ge3—O6ii105.11
O2—Ge1—O4106.56O3—Ge3—O6101.98
O2—Ge1—O5109.66O3—Ge3—O6ii106.44
O4—Ge1—O5127.76O6—Ge3—O6ii134.25
O2—Ge2—O399.73Ge1—O1—Ge3139.51
O2—Ge2—O4i104.54Ge1—O2—Ge2141.40
O2—Ge2—O5i101.16Ge2—O3—Ge3138.11
O3—Ge2—O4i108.38Ge1—O4—Ge2iii39.47
O3—Ge2—O5i109.31Ge1—O5—Ge2iii39.19
O4i—Ge2—O5i129.31Ge3—O6—Ge3ii38.59
O2—Ge1—O1—Ge33.32O5i—Ge2—O3—Ge3106.33
O4—Ge1—O1—Ge3113.15O2—Ge2—O4i—Ge1i160.88
O5—Ge1—O1—Ge3110.28O3—Ge2—O4i—Ge1i93.45
O1—Ge1—O2—Ge24.44O2—Ge2—O5i—Ge1i162.43
O4—Ge1—O2—Ge2112.30O3—Ge2—O5i—Ge1i93.00
O5—Ge1—O2—Ge2106.02O3—Ge3—O1—Ge11.94
O1—Ge1—O4—Ge2iii164.67O6—Ge3—O1—Ge1107.40
O2—Ge1—O4—Ge2iii90.85O6ii—Ge3—O1—Ge1108.90
O5—Ge1—O4—Ge2iii41.54O1—Ge3—O3—Ge20.26
O1—Ge1—O5—Ge2iii163.79O6—Ge3—O3—Ge2106.70
O2—Ge1—O5—Ge2iii89.96O6ii—Ge3—O3—Ge2109.55
O4—Ge1—O5—Ge2iii41.30O1—Ge3—O6—Ge3ii93.54
O3—Ge2—O2—Ge13.54O3—Ge3—O6—Ge3ii161.16
O4i—Ge2—O2—Ge1108.48O6ii—Ge3—O6—Ge3ii33.53
O5i—Ge2—O2—Ge1115.61O1—Ge3—O6ii—Ge3ii92.11
O2—Ge2—O3—Ge30.78O3—Ge3—O6ii—Ge3ii160.44
O4i—Ge2—O3—Ge3108.21O6—Ge3—O6ii—Ge3ii34.31
Symmetry codes: (i) x+1/2, y1/2, z+1/2; (ii) x, y, z+1/2; (iii) x+1/2, y+1/2, z+1/2.

Experimental details

Crystal data
Chemical formulaGe3O9·3(Ba)
Mr257.94
Crystal system, space groupMonoclinic, C2/c
Temperature (K)299
a, b, c (Å)13.18949 (15), 7.62045 (5), 11.71698 (9)
β (°) 112.2783 (7)
V3)1089.76 (2)
Z12
Radiation type?, λ = 1.540560 Å
µ (mm1)5.8
Specimen shape, size (mm)Flat_sheet, 8 × 8
Data collection
DiffractometerSTOE STADI MP
diffractometer
Specimen mounting?
Data collection modeTransmission
Scan method?
2θ values (°)2θmin = 2.053 2θmax = 129.983 2θstep = 0.010
Refinement
R factors and goodness of fitRp = 3.303, Rwp = 4.268, Rexp = 3.159, RBragg = 4.542, χ2 = 3.349
No. of data points12794
No. of parameters62
No. of restraints12

Computer programs: STOE WinXPow, intuitive, FULLPROF.

Selected geometric parameters (Å, º) top
Ge1—O11.7685Ge2—O4i1.6936
Ge1—O21.7734Ge2—O5i1.7118
Ge1—O41.7110Ge3—O11.7778
Ge1—O51.7166Ge3—O31.7714
Ge2—O21.7800Ge3—O61.6849
Ge2—O31.7950Ge3—O6ii1.7197
O1—Ge1—O299.38O1—Ge3—O3101.76
O1—Ge1—O4104.10O1—Ge3—O6103.22
O1—Ge1—O5105.66O1—Ge3—O6ii105.11
O2—Ge1—O4106.56O3—Ge3—O6101.98
O2—Ge1—O5109.66O3—Ge3—O6ii106.44
O4—Ge1—O5127.76O6—Ge3—O6ii134.25
O2—Ge2—O399.73Ge1—O1—Ge3139.51
O2—Ge2—O4i104.54Ge1—O2—Ge2141.40
O2—Ge2—O5i101.16Ge2—O3—Ge3138.11
O3—Ge2—O4i108.38Ge1—O4—Ge2iii39.47
O3—Ge2—O5i109.31Ge1—O5—Ge2iii39.19
O4i—Ge2—O5i129.31Ge3—O6—Ge3ii38.59
Symmetry codes: (i) x+1/2, y1/2, z+1/2; (ii) x, y, z+1/2; (iii) x+1/2, y+1/2, z+1/2.
 

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