Download citation
Download citation
link to html
Tetrahedrally coordinated oxides usually present polymorphism, but for NaGaO2, only the β polymorph has been reported. In this work, the synthesis and structural characterization of γ-sodium gallate, γ-NaGaO2, are presented. The crystal structure belongs to the orthorhombic system, space group Pbca (No. 61), and has been characterized by a Rietveld refinement of the X-ray powder diffraction pattern. The structure is similar to those exhibited by the γ phases of many tetrahedral oxides.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270102003049/br1357sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270102003049/br1357Isup2.hkl
Contains datablock I

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0108270102003049/br1357Isup3.rtv
Contains datablock I

Comment top

NaGaO2 belongs to the group of tetrahedrally coordinated oxides with the general formula ABO2, where A is Li or Na 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.

The first group is known as the low-temperature β phase, having the basic wurtzite structure, and the second group is the high-temperature γ phase, where the crystal structure presents the cations distributed over two different sets of available tetrahedral sites.

In addition to these β and γ polymorphic phases, a low-temperature and sometimes high-pressure α form occurs (West, 1975).

Vielhaber & Hoppe (1969) and Müller & Hoppe (1992) have reported crystal data for the β phase of NaGaO2, but no reports exist to date concerning the synthesis or crystal characterization of the γ phase of NaGaO2, which is reported here.

Experimental top

The γ polymorph of NaGaO2 was synthesized by a solid-state reaction. The starting materials were Na2CO3 (99.7%, Baker) and Ga2O3 (99.99%, Aldrich). A mixture (ratio?) totalling 10 g was prepared by weighing Na2CO3 and Ga2O3 and mixing them into a paste with acetone in an agate mortar. The mixture was fired in an electric muffle furnace, whose temperature was controlled and measured. Initial firing was at 873–973 K for a few hours to expel CO2, followed by 6 d at 1323 K and quenching in ice to room temperature.

Refinement top

The positions of 37 resolvable peaks were input to the LSUCRI program for least-squares unit-cell refinement (Garvey, 1986). The starting set of cell parameters for the refinement was taken from the data reported by Grey et al. (1990) for the isostructural compound KGaO2. The close values observed for the full width at half-maximum (FWHM; 0.12° at 28.446°), corresponding to the 111 peak of Si, NBS 640BC, used as external standard, and that for the 231 peak, belonging to the sample (FWHM = 0.124° at 29.962°), indicate a high degree of crystallinity in the specimen. The powder diffraction data were refined by the Rietveld method, using the coordinates reported for KGaO2 as starting parameters for the refinement. A pseudo-Voigt function modified by Thompson et al. (1987) was chosen to generate the line shape of the diffraction peaks. The background was fitted to a polynomial refinable function. The following parameters were refined in the space group Pbca: zero point, scale factor, six background polynomial coefficients, unit-cell dimensions, half-width, pseudo-Voigt and asymmetry parameters for the peak shape, and positional and isotropic displacement parameters. The FULLPROF program for Rietveld refinement and pattern-matching analysis (unpublished) is a strongly modified version (by Juan Rodríguez-Carvajal) of that described by Wiles & Young (1987).

Computing details top

Data collection: DIFFRAC/AT (Siemens, 1993); cell refinement: LSUCRI (Garvey, 1986); data reduction: Please provide missing details; program(s) used to solve structure: Please provide missing details; program(s) used to refine structure: FULLPROF (unpublished); molecular graphics: ATOMS (Dowty, 1994); software used to prepare material for publication: ATOMS.

Figures top
[Figure 1] Fig. 1. Comparison of the observed (+) and calculated (solid line) intensities for γ NaGaO2. The difference pattern is given below.
[Figure 2] Fig. 2. A view of the unit cell of γ NaGaO2. Note that some tetrahedra point downwards and others point upwards. GaO4 tetrahedra are white and NaO4 tetrahedra are dark grey.
γ sodium gallate top
Crystal data top
NaGaO2Z = 16
Mr = 124.71Cu Kα1, Cu Kα2 radiation, λ = 1.54056, 1.544 Å
Orthorhombic, PbcaT = 295 K
a = 5.3145 (2) Åwhite
b = 10.6234 (5) Åflat sheet, 20 × 20 mm
c = 14.7782 (7) ÅSpecimen preparation: Prepared at 1323 K
V = 834.36 (7) Å3
Data collection top
Siemens D5000
diffractometer
Data collection mode: reflection
Radiation source: sealed X-ray tube, Cu KαScan method: step
Graphite monochromator2θmin = 10°, 2θmax = 90°, 2θstep = 0.02°
Specimen mounting: packed powder sample container
Refinement top
Least-squares matrix: full with fixed elements per cycle4001 data points
Rp = 0.12Profile function: 'pseudo-Voigt modified by Thompson et al. (1987)'
Rwp = ?47 parameters
Rexp = 0.11
RBragg = 0.05Background function: polynomial
R(F2) = 0.04Preferred orientation correction: none
χ2 = 2.190
Crystal data top
NaGaO2V = 834.36 (7) Å3
Mr = 124.71Z = 16
Orthorhombic, PbcaCu Kα1, Cu Kα2 radiation, λ = 1.54056, 1.544 Å
a = 5.3145 (2) ÅT = 295 K
b = 10.6234 (5) Åflat sheet, 20 × 20 mm
c = 14.7782 (7) Å
Data collection top
Siemens D5000
diffractometer
Scan method: step
Specimen mounting: packed powder sample container2θmin = 10°, 2θmax = 90°, 2θstep = 0.02°
Data collection mode: reflection
Refinement top
Rp = 0.12R(F2) = 0.04
Rwp = ?χ2 = 2.190
Rexp = 0.114001 data points
RBragg = 0.0547 parameters
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Ga10.1957 (5)0.0245 (3)0.1874 (4)0.0065 (6)
Ga20.3085 (6)0.2767 (3)0.0618 (3)0.0065 (6)
Na10.717 (2)0.985 (1)0.066 (1)0.020 (1)
Na20.815 (2)0.273 (1)0.190 (1)0.020 (1)
O10.640 (3)0.274 (1)0.040 (1)0.005 (1)
O20.212 (2)0.442 (1)0.083 (1)0.005 (1)
O30.225 (2)0.194 (2)0.170 (1)0.005 (1)
O40.134 (3)0.481 (1)0.289 (1)0.005 (1)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
???????
Geometric parameters (Å, º) top
Ga1—O21.84 (2)Na1—O12.39 (2)
Ga1—O31.83 (2)Na1—O22.33 (2)
Ga1—O41.85 (2)Na1—O2'2.34 (2)
Ga1—O4'1.81 (2)Na1—O42.29 (2)
Ga2—O11.79 (2)Na2—O12.40 (2)
Ga2—O1'1.83 (2)Na2—O32.35 (1)
Ga2—O21.85 (2)Na2—O3'2.29 (2)
Ga2—O31.87 (2)Na2—O42.43 (2)
O2—Ga1—O3109.1 (14)O1—Na1—O299.6 (10)
O2—Ga1—O4107.0 (13)O1—Na1—O2'98.3 (9)
O2—Ga1—O4'116.0 (14)O1—Na1—O491.2 (10)
O3—Ga1—O4110.8 (13)O2—Na1—O2'99.1 (10)
O3—Ga1—O4'109.1 (13)O2—Na1—O4153.3 (13)
O4—Ga1—O4'104.7 (13)O2'—Na1—O4103.4 (10)
O1—Ga2—O1'109.2 (13)O1—Na2—O3104.2 (10)
O1—Ga2—O2108.5 (12)O1—Na2—O3'139.2 (13)
O1—Ga2—O3112.2 (13)O1—Na2—O487.8 (10)
O1'—Ga2—O2106.5 (13)O3—Na2—O3'100.2 (10)
O1'—Ga2—O3116.5 (14)O3—Na2—O4135.0 (10)
O2—Ga2—O3103.5 (13)O3'—Na2—O497.6 (10)

Experimental details

Crystal data
Chemical formulaNaGaO2
Mr124.71
Crystal system, space groupOrthorhombic, Pbca
Temperature (K)295
a, b, c (Å)5.3145 (2), 10.6234 (5), 14.7782 (7)
V3)834.36 (7)
Z16
Radiation typeCu Kα1, Cu Kα2, λ = 1.54056, 1.544 Å
Specimen shape, size (mm)Flat sheet, 20 × 20
Data collection
DiffractometerSiemens D5000
diffractometer
Specimen mountingPacked powder sample container
Data collection modeReflection
Scan methodStep
2θ values (°)2θmin = 10 2θmax = 90 2θstep = 0.02
Refinement
R factors and goodness of fitRp = 0.12, Rwp = ?, Rexp = 0.11, RBragg = 0.05, R(F2) = 0.04, χ2 = 2.190
No. of data points4001
No. of parameters47
No. of restraints?

Computer programs: DIFFRAC/AT (Siemens, 1993), LSUCRI (Garvey, 1986), Please provide missing details, FULLPROF (unpublished), ATOMS (Dowty, 1994), ATOMS.

Selected bond lengths (Å) top
Ga1—O21.84 (2)Na1—O12.39 (2)
Ga1—O31.83 (2)Na1—O22.33 (2)
Ga1—O41.85 (2)Na1—O2'2.34 (2)
Ga1—O4'1.81 (2)Na1—O42.29 (2)
Ga2—O11.79 (2)Na2—O12.40 (2)
Ga2—O1'1.83 (2)Na2—O32.35 (1)
Ga2—O21.85 (2)Na2—O3'2.29 (2)
Ga2—O31.87 (2)Na2—O42.43 (2)
 

Follow Acta Cryst. C
Sign up for e-alerts
Follow Acta Cryst. on Twitter
Follow us on facebook
Sign up for RSS feeds