γ-Sodium gallate: A rietveld refinement using X-ray powder diffraction

Article abstract of DOI:10.1107/S0108270102003049

The synthesis and the structural characterization of γ-sodium gallate was presented. The crystal structure was found to belong to the orthorhombic system and was characterized by a Rietveld refinement of the x-ray powder diffraction pattern. The structure of this compound was similar to the structures exhibited by the γ phases of many tetrahedral oxides.

Full text of DOI:10.1107/S0108270102003049

inorganic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
ISSN 0108-2701
c-Sodium gallate: a Rietveld refine-
ment using X-ray powder diffraction
Figure 2
A view of part of the structure of ꢁ-NaGaO
point downwards and others point upwards. GaO
and NaO tetrahedra are grey.
2
. Note that some tetrahedra
tetrahedra are white
a
b
4
Mar Âõ a-Elena Villafuerte-Castrej o n, * Lauro Bucio, Angel
4
a
c
c
S a nchez-Arjona, Julio Duque and Ram o n Pom e s
The ®rst group is known as the low-temperature ꢀ phase,
having the basic wurtzite structure, and the second group is
the high-temperature ꢁ phase, where the crystal structure
presents the cations distributed over two different sets of
available tetrahedral sites.
a
Instituto de Investigaciones en Materiales, Universidad Nacional Aut o noma de
b
M e xico, AP 70-360, 04510 M e xico DF, Mexico, Instituto de F Âõ sica, Universidad
Nacional Aut o noma de M e xico, AP 20-364, 01000 M e xico DF, Mexico, and
c
National Center for Scientific Research, PO Box 6880, Havana, Cuba
Correspondence e-mail: mevc@servidor.unam.mx
In addition to these ꢀ and ꢁ polymorphic phases, a low-
temperature, and sometimes high-pressure, ꢂ form occurs
Received 12 January 2002
Accepted 13 February 2002
Online 30 April 2002
(West, 1975).
Vielhaber & Hoppe (1969) and M uÈ ller & Hoppe (1992)
have reported crystal data for the ꢀ phase of NaGaO , but no
Tetrahedrally coordinated oxides usually present poly-
morphism, but for NaGaO , only the ꢀ polymorph has been
2
reports exist to date concerning the synthesis or crystal char-
acterization of the ꢁ phase of NaGaO , which is reported here.
2
reported. In this work, the synthesis and structural character-
ization of ꢁ-sodium gallate, ꢁ-NaGaO , are presented. The
2
2
crystal structure belongs to the orthorhombic system, space
group Pbca (No. 61), and has been characterized by a Rietveld
re®nement of the X-ray powder diffraction pattern. The
structure is similar to those exhibited by the ꢁ phases of many
tetrahedral oxides.
Experimental
The ꢁ polymorph of NaGaO
tion. The starting materials were Na
99.99%, Aldrich). A mixture totalling 10 g was prepared by weighing
Na CO and Ga , and mixing them into a paste with acetone in an
2
was synthesized by a solid-state reac-
2
CO (99.7%, Baker) and Ga O
3
2 3
(
2
3
2 3
O
agate mortar. The mixture was ®red in an electric muf¯e furnace,
whose temperature was controlled and measured. Initial ®ring was at
Comment
8
2
73±973 K for a few hours to expel CO , followed by 6 d at 1323 K
NaGaO belongs to the group of tetrahedrally coordinated
2
and quenching in ice to room temperature.
oxides with the general formula ABO , where A is Li or Na
2
and B is Al, Ga or Fe (B is Fe only when A is Na). These
oxides are usually polymorphic and the polymorphs fall into
two groups.
Crystal data
NaGaO
= 124.71
2
Density measured by picnometry
Cu Kꢂ and Cu Kꢂ radiation
ꢃ = 1.713 mm
T = 295 K
M
r
1
2
�
1
Orthorhombic, Pbca
Ê
a = 5.3145 (2) A
b = 10.6234 (5) A
c = 14.7782 (7) A
Ê
V = 834.36 (7) A
Ê
Ê
Specimen shape: ¯at sheet
20 Â 20 Â 0.2 mm
3
Particle morphology: no speci®c
colour, white
Specimen prepared at 1323 K
Z = 16
�
3
D
D
x
= 3.97 Mg m
= 3.6 Mg m
�
3
m
Data collection
Siemens D5000 diffractometer
Specimen mounting: packed powder
sample container
Specimen mounted in re¯ection
mode
ꢀ
2ꢄmin = 10, 2ꢄmax = 90
ꢀ
Increment in 2ꢄ = 0.02
Re®nement
R
R
R
p
= 0.12
exp = 0.11
= 0.05
Pro®le function: pseudo-Voigt
modi®ed by Thompson et al.
(1987)
B
S = 1.48
min = 10, 2ꢄmax = 90
Increment in 2ꢄ = 0.02
Wavelength of incident radiation:
363 re¯ections
47 parameters
Preferred orientation correction:
none
ꢀ
2ꢄ
ꢀ
Figure 1
Comparison of the observed (+) and calculated (solid line) intensities for
Ê
Cu Kꢂ
Cu Kꢂ
1
2
= 1.541 A
Ê
= 1.544 A
ꢁ
-NaGaO
2
. The difference pattern is given underneath.
Acta Cryst. (2002). C58, i69±i70
DOI: 10.1107/S0108270102003049
# 2002 International Union of Crystallography i69

inorganic compounds
Table 1
Selected interatomic distances (A).
Rietveld re®nement and pattern-matching analysis (Juan Rodr õÂ guez-
Carvajal; unpublished) is a modi®ed version of that described by
Wiles & Young (1981).
Ê
Ga1ÐO2
Ga1ÐO3
Ga1ÐO4
Ga1ÐO4
Ga2ÐO1
Ga2ÐO1
Ga2ÐO2
Ga2ÐO3
1.84 (2)
1.83 (2)
1.85 (2)
1.81 (2)
1.79 (2)
1.83 (2)
1.85 (2)
1.87 (2)
Na1ÐO1
Na1ÐO2
Na1ÐO2
Na1ÐO4
Na2ÐO1
Na2ÐO3
Na2ÐO3
Na2ÐO4
2.39 (2)
2.33 (2)
2.34 (2)
2.29 (2)
2.40 (2)
2.35 (1)
2.29 (2)
2.43 (2)
Data collection: DIFFRAC/AT (Siemens, 1993); cell re®nement:
LSUCRI (Garvey, 1986); program(s) used to re®ne structure:
FULLPROF (Rodr õÂ guez-Carvajal; unpublished); molecular graphics:
ATOMS (Dowty, 1994); software used to prepare material for
publication: ATOMS.
iii
i
ii
i
1
2
1
2
1
2
1
2
We are grateful for ®nancial support from CONACyT
project No. 33361-U and from DGAPA-PAPIIT IN-102700.
Symmetry codes: (i) + x, y, � z; (ii) + x, � y, � z; (iii) � x, � y, � z.
The positions of 37 resolvable peaks were input into the LSUCRI
program for least-squares unit-cell re®nement (Garvey, 1986). The
starting set of cell parameters for the re®nement was taken from the
data reported by Grey et al. (1990) for the isostructural compound
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: BR1357). Services for accessing these data are
described at the back of the journal.
KGaO
FWHM; 0.12 at 28.446 ), corresponding to the 111 peak of Si (Natl
Bur. Stand. 640BC) used as external standard, and that for the 231
2
. The close values observed for the full width at half-maximum
ꢀ
ꢀ
(
ꢀ
ꢀ
References
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high degree of crystallinity in the specimen. The powder diffraction
data were re®ned by the Rietveld method, using the coordinates
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2
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modi®ed by Thompson et al. (1987) was chosen to generate the line
shape of the diffraction peaks. The background was ®tted to a
polynomial re®nable function. The following parameters were re®ned
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isotropic displacement parameters. The FULLPROF program for
2
19.
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i70 Mar Âõ a-Elena Villafuerte-Castrej o n et al.
ꢁ
NaGaO
Acta Cryst. (2002). C58, i69±i70
2