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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
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.
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(unpublished) is a strongly modified version (by Juan Rodríguez-Carvajal) of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).
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.
Crystal data top
NaGaO2 | Z = 16 |
Mr = 124.71 | Cu Kα1, Cu Kα2 radiation, λ = 1.54056, 1.544 Å |
Orthorhombic, Pbca | T = 295 K |
a = 5.3145 (2) Å | white |
b = 10.6234 (5) Å | flat sheet, 20 × 20 mm |
c = 14.7782 (7) Å | Specimen 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 Kα | Scan method: step |
Graphite monochromator | 2θmin = 10°, 2θmax = 90°, 2θstep = 0.02° |
Specimen mounting: packed powder sample container | |
Refinement top
Least-squares matrix: full with fixed elements per cycle | 4001 data points |
Rp = 0.12 | Profile function: 'pseudo-Voigt modified by Thompson et al. (1987)' |
Rwp = ? | 47 parameters |
Rexp = 0.11 | |
RBragg = 0.05 | Background function: polynomial |
R(F2) = 0.04 | Preferred orientation correction: none |
χ2 = 2.190 | |
Crystal data top
NaGaO2 | V = 834.36 (7) Å3 |
Mr = 124.71 | Z = 16 |
Orthorhombic, Pbca | Cu Kα1, Cu Kα2 radiation, λ = 1.54056, 1.544 Å |
a = 5.3145 (2) Å | T = 295 K |
b = 10.6234 (5) Å | flat sheet, 20 × 20 mm |
c = 14.7782 (7) Å | |
Data collection top
Siemens D5000 diffractometer | Scan method: step |
Specimen mounting: packed powder sample container | 2θmin = 10°, 2θmax = 90°, 2θstep = 0.02° |
Data collection mode: reflection | |
Refinement top
Rp = 0.12 | R(F2) = 0.04 |
Rwp = ? | χ2 = 2.190 |
Rexp = 0.11 | 4001 data points |
RBragg = 0.05 | 47 parameters |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
Ga1 | 0.1957 (5) | 0.0245 (3) | 0.1874 (4) | 0.0065 (6) | |
Ga2 | 0.3085 (6) | 0.2767 (3) | 0.0618 (3) | 0.0065 (6) | |
Na1 | 0.717 (2) | 0.985 (1) | 0.066 (1) | 0.020 (1) | |
Na2 | 0.815 (2) | 0.273 (1) | 0.190 (1) | 0.020 (1) | |
O1 | 0.640 (3) | 0.274 (1) | 0.040 (1) | 0.005 (1) | |
O2 | 0.212 (2) | 0.442 (1) | 0.083 (1) | 0.005 (1) | |
O3 | 0.225 (2) | 0.194 (2) | 0.170 (1) | 0.005 (1) | |
O4 | 0.134 (3) | 0.481 (1) | 0.289 (1) | 0.005 (1) | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
? | ? | ? | ? | ? | ? | ? |
Geometric parameters (Å, º) top
Ga1—O2 | 1.84 (2) | Na1—O1 | 2.39 (2) |
Ga1—O3 | 1.83 (2) | Na1—O2 | 2.33 (2) |
Ga1—O4 | 1.85 (2) | Na1—O2' | 2.34 (2) |
Ga1—O4' | 1.81 (2) | Na1—O4 | 2.29 (2) |
Ga2—O1 | 1.79 (2) | Na2—O1 | 2.40 (2) |
Ga2—O1' | 1.83 (2) | Na2—O3 | 2.35 (1) |
Ga2—O2 | 1.85 (2) | Na2—O3' | 2.29 (2) |
Ga2—O3 | 1.87 (2) | Na2—O4 | 2.43 (2) |
| | | |
O2—Ga1—O3 | 109.1 (14) | O1—Na1—O2 | 99.6 (10) |
O2—Ga1—O4 | 107.0 (13) | O1—Na1—O2' | 98.3 (9) |
O2—Ga1—O4' | 116.0 (14) | O1—Na1—O4 | 91.2 (10) |
O3—Ga1—O4 | 110.8 (13) | O2—Na1—O2' | 99.1 (10) |
O3—Ga1—O4' | 109.1 (13) | O2—Na1—O4 | 153.3 (13) |
O4—Ga1—O4' | 104.7 (13) | O2'—Na1—O4 | 103.4 (10) |
O1—Ga2—O1' | 109.2 (13) | O1—Na2—O3 | 104.2 (10) |
O1—Ga2—O2 | 108.5 (12) | O1—Na2—O3' | 139.2 (13) |
O1—Ga2—O3 | 112.2 (13) | O1—Na2—O4 | 87.8 (10) |
O1'—Ga2—O2 | 106.5 (13) | O3—Na2—O3' | 100.2 (10) |
O1'—Ga2—O3 | 116.5 (14) | O3—Na2—O4 | 135.0 (10) |
O2—Ga2—O3 | 103.5 (13) | O3'—Na2—O4 | 97.6 (10) |
Experimental details
Crystal data |
Chemical formula | NaGaO2 |
Mr | 124.71 |
Crystal system, space group | Orthorhombic, Pbca |
Temperature (K) | 295 |
a, b, c (Å) | 5.3145 (2), 10.6234 (5), 14.7782 (7) |
V (Å3) | 834.36 (7) |
Z | 16 |
Radiation type | Cu Kα1, Cu Kα2, λ = 1.54056, 1.544 Å |
Specimen shape, size (mm) | Flat sheet, 20 × 20 |
|
Data collection |
Diffractometer | Siemens D5000 diffractometer |
Specimen mounting | Packed powder sample container |
Data collection mode | Reflection |
Scan method | Step |
2θ values (°) | 2θmin = 10 2θmax = 90 2θstep = 0.02 |
|
Refinement |
R factors and goodness of fit | Rp = 0.12, Rwp = ?, Rexp = 0.11, RBragg = 0.05, R(F2) = 0.04, χ2 = 2.190 |
No. of data points | 4001 |
No. of parameters | 47 |
No. of restraints | ? |
Selected bond lengths (Å) topGa1—O2 | 1.84 (2) | Na1—O1 | 2.39 (2) |
Ga1—O3 | 1.83 (2) | Na1—O2 | 2.33 (2) |
Ga1—O4 | 1.85 (2) | Na1—O2' | 2.34 (2) |
Ga1—O4' | 1.81 (2) | Na1—O4 | 2.29 (2) |
Ga2—O1 | 1.79 (2) | Na2—O1 | 2.40 (2) |
Ga2—O1' | 1.83 (2) | Na2—O3 | 2.35 (1) |
Ga2—O2 | 1.85 (2) | Na2—O3' | 2.29 (2) |
Ga2—O3 | 1.87 (2) | Na2—O4 | 2.43 (2) |
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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.