Atomic and domain structure of the low-temperature phase of barium metagermanate (BaGeO3)

Többens, D.M.; Kahlenberg, V.; Gspan, C.; Kothleitner, G.

doi:10.1107/S0108768106039140

Atomic and domain structure of the low-temperature phase of barium metagermanate (BaGeO₃)

D. M. Többens, V. Kahlenberg, C. Gspan and G. Kothleitner

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.

Keywords: germanates; layer structure; disorder.

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Supporting information

	Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768106039140/ws5051sup1.cif Contains datablocks global, BaGeO3, BaGeO3-TM
	Rietveld powder data file (CIF format) https://doi.org/10.1107/S0108768106039140/ws5051sup2.rtv Contains datablock BaGeO3
	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

(BaGeO3) top

Crystal data top

Ge₃O₉·3(Ba)	V = 1089.76 (2) Å³
M_r = 257.94	Z = 12
Monoclinic, C2/c	? radiation, λ = 1.540560 Å
Hall symbol: -C 2yc	µ = 5.8 mm⁻¹
a = 13.18949 (15) Å	T = 299 K
b = 7.62045 (5) Å	white
c = 11.71698 (9) Å	flat_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 tube	T_min = ?, T_max = ?
Asymmetric Ge(111) monochromator	2θ_min = 2.053°, 2θ_max = 129.983°, 2θ_step = 0.010°
Data collection mode: transmission

Refinement top

R_p = 3.303	12794 data points
R_wp = 4.268	62 parameters
R_exp = 3.159	12 restraints
R_Bragg = 4.542
χ² = 3.349

Crystal data top

Ge₃O₉·3(Ba)	V = 1089.76 (2) Å³
M_r = 257.94	Z = 12
Monoclinic, C2/c	? radiation, λ = 1.540560 Å
a = 13.18949 (15) Å	µ = 5.8 mm⁻¹
b = 7.62045 (5) Å	T = 299 K
c = 11.71698 (9) Å	flat_sheet, 8 × 8 mm
β = 112.2783 (7)°

Data collection top

STOE STADI MP diffractometer	T_min = ?, T_max = ?
Data collection mode: transmission	2θ_min = 2.053°, 2θ_max = 129.983°, 2θ_step = 0.010°
Absorption correction: empirical (using intensity measurements) from beam loss ?

Refinement top

R_p = 3.303	χ² = 3.349
R_wp = 4.268	12794 data points
R_exp = 3.159	62 parameters
R_Bragg = 4.542	12 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

	x	y	z	U_iso*/U_eq	Occ. (<1)
Ba1	0.0838 (3)	0.2521 (4)	0.5001 (6)	0.0093 (2)*
Ba2	0.25000	0.25000	0.00000	0.0093 (2)*
Ge1	0.6592 (5)	0.8371 (7)	0.2505 (5)	0.0093 (2)*	0.50000
Ge2	0.7953 (5)	0.4653 (8)	0.2508 (5)	0.0093 (2)*	0.50000
Ge3	0.5429 (4)	0.4497 (7)	0.2508 (5)	0.0093 (2)*	0.50000
O1	0.5593 (15)	0.6811 (11)	0.249 (3)	0.0093 (2)*	0.50000
O2	0.7634 (16)	0.6927 (12)	0.247 (3)	0.0093 (2)*	0.50000
O3	0.670 (2)	0.3739 (17)	0.251 (6)	0.0093 (2)*	0.50000
O4	0.6051 (13)	0.934 (2)	0.1082 (7)	0.0093 (2)*
O5	0.6999 (16)	0.937 (2)	0.3920 (7)	0.0093 (2)*
O6	0.4572 (12)	0.404 (3)	0.1055 (7)	0.0093 (2)*

Geometric parameters (Å, º) top

Ge1—O1	1.7685	Ge2—O4ⁱ	1.6936
Ge1—O2	1.7734	Ge2—O5ⁱ	1.7118
Ge1—O4	1.7110	Ge3—O1	1.7778
Ge1—O5	1.7166	Ge3—O3	1.7714
Ge2—O2	1.7800	Ge3—O6	1.6849
Ge2—O3	1.7950	Ge3—O6ⁱⁱ	1.7197

O1—Ge1—O2	99.38	O1—Ge3—O3	101.76
O1—Ge1—O4	104.10	O1—Ge3—O6	103.22
O1—Ge1—O5	105.66	O1—Ge3—O6ⁱⁱ	105.11
O2—Ge1—O4	106.56	O3—Ge3—O6	101.98
O2—Ge1—O5	109.66	O3—Ge3—O6ⁱⁱ	106.44
O4—Ge1—O5	127.76	O6—Ge3—O6ⁱⁱ	134.25
O2—Ge2—O3	99.73	Ge1—O1—Ge3	139.51
O2—Ge2—O4ⁱ	104.54	Ge1—O2—Ge2	141.40
O2—Ge2—O5ⁱ	101.16	Ge2—O3—Ge3	138.11
O3—Ge2—O4ⁱ	108.38	Ge1—O4—Ge2ⁱⁱⁱ	39.47
O3—Ge2—O5ⁱ	109.31	Ge1—O5—Ge2ⁱⁱⁱ	39.19
O4ⁱ—Ge2—O5ⁱ	129.31	Ge3—O6—Ge3ⁱⁱ	38.59

O2—Ge1—O1—Ge3	3.32	O5ⁱ—Ge2—O3—Ge3	−106.33
O4—Ge1—O1—Ge3	113.15	O2—Ge2—O4ⁱ—Ge1ⁱ	−160.88
O5—Ge1—O1—Ge3	−110.28	O3—Ge2—O4ⁱ—Ge1ⁱ	93.45
O1—Ge1—O2—Ge2	−4.44	O2—Ge2—O5ⁱ—Ge1ⁱ	162.43
O4—Ge1—O2—Ge2	−112.30	O3—Ge2—O5ⁱ—Ge1ⁱ	−93.00
O5—Ge1—O2—Ge2	106.02	O3—Ge3—O1—Ge1	−1.94
O1—Ge1—O4—Ge2ⁱⁱⁱ	164.67	O6—Ge3—O1—Ge1	−107.40
O2—Ge1—O4—Ge2ⁱⁱⁱ	−90.85	O6ⁱⁱ—Ge3—O1—Ge1	108.90
O5—Ge1—O4—Ge2ⁱⁱⁱ	41.54	O1—Ge3—O3—Ge2	0.26
O1—Ge1—O5—Ge2ⁱⁱⁱ	−163.79	O6—Ge3—O3—Ge2	106.70
O2—Ge1—O5—Ge2ⁱⁱⁱ	89.96	O6ⁱⁱ—Ge3—O3—Ge2	−109.55
O4—Ge1—O5—Ge2ⁱⁱⁱ	−41.30	O1—Ge3—O6—Ge3ⁱⁱ	−93.54
O3—Ge2—O2—Ge1	3.54	O3—Ge3—O6—Ge3ⁱⁱ	161.16
O4ⁱ—Ge2—O2—Ge1	−108.48	O6ⁱⁱ—Ge3—O6—Ge3ⁱⁱ	33.53
O5ⁱ—Ge2—O2—Ge1	115.61	O1—Ge3—O6ⁱⁱ—Ge3ⁱⁱ	92.11
O2—Ge2—O3—Ge3	−0.78	O3—Ge3—O6ⁱⁱ—Ge3ⁱⁱ	−160.44
O4ⁱ—Ge2—O3—Ge3	108.21	O6—Ge3—O6ⁱⁱ—Ge3ⁱⁱ	−34.31

Symmetry codes: (i) −x+1/2, y−1/2, −z+1/2; (ii) −x, y, −z+1/2; (iii) −x+1/2, y+1/2, −z+1/2.

Experimental details

Crystal data
Chemical formula	Ge₃O₉·3(Ba)
M_r	257.94
Crystal system, space group	Monoclinic, C2/c
Temperature (K)	299
a, b, c (Å)	13.18949 (15), 7.62045 (5), 11.71698 (9)
β (°)	112.2783 (7)
V (Å³)	1089.76 (2)
Z	12
Radiation type	?, λ = 1.540560 Å
µ (mm⁻¹)	5.8
Specimen shape, size (mm)	Flat_sheet, 8 × 8

Data collection
Diffractometer	STOE STADI MP diffractometer
Specimen mounting	?
Data collection mode	Transmission
Scan method	?
2θ values (°)	2θ_min = 2.053 2θ_max = 129.983 2θ_step = 0.010

Refinement
R factors and goodness of fit	R_p = 3.303, R_wp = 4.268, R_exp = 3.159, R_Bragg = 4.542, χ² = 3.349
No. of data points	12794
No. of parameters	62
No. of restraints	12

Computer programs: STOE WinXPow, intuitive, FULLPROF.

Selected geometric parameters (Å, º) top

Ge1—O1	1.7685	Ge2—O4ⁱ	1.6936
Ge1—O2	1.7734	Ge2—O5ⁱ	1.7118
Ge1—O4	1.7110	Ge3—O1	1.7778
Ge1—O5	1.7166	Ge3—O3	1.7714
Ge2—O2	1.7800	Ge3—O6	1.6849
Ge2—O3	1.7950	Ge3—O6ⁱⁱ	1.7197

O1—Ge1—O2	99.38	O1—Ge3—O3	101.76
O1—Ge1—O4	104.10	O1—Ge3—O6	103.22
O1—Ge1—O5	105.66	O1—Ge3—O6ⁱⁱ	105.11
O2—Ge1—O4	106.56	O3—Ge3—O6	101.98
O2—Ge1—O5	109.66	O3—Ge3—O6ⁱⁱ	106.44
O4—Ge1—O5	127.76	O6—Ge3—O6ⁱⁱ	134.25
O2—Ge2—O3	99.73	Ge1—O1—Ge3	139.51
O2—Ge2—O4ⁱ	104.54	Ge1—O2—Ge2	141.40
O2—Ge2—O5ⁱ	101.16	Ge2—O3—Ge3	138.11
O3—Ge2—O4ⁱ	108.38	Ge1—O4—Ge2ⁱⁱⁱ	39.47
O3—Ge2—O5ⁱ	109.31	Ge1—O5—Ge2ⁱⁱⁱ	39.19
O4ⁱ—Ge2—O5ⁱ	129.31	Ge3—O6—Ge3ⁱⁱ	38.59

Symmetry codes: (i) −x+1/2, y−1/2, −z+1/2; (ii) −x, y, −z+1/2; (iii) −x+1/2, y+1/2, −z+1/2.

Format		BIBTeX
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Format		BIBTeX
		EndNote
		RefMan
		Refer
		Medline
		CIF
		SGML
		Text
		Plain Text

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