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Acta Crystallogr Sect E Struct Rep Online. 2009 August 1; 65(Pt 8): i60.
Published online 2009 July 15. doi:  10.1107/S1600536809026579
PMCID: PMC2977227

Rietveld refinement of Y2GeO5

Abstract

Y2GeO5 (yttrium germanium penta­oxide) was synthesized by solid-state reaction at 1443 K. The arrangement, which has monoclinic symmetry, is isostructural with Dy2GeO5 and presents two independent sites for the Y atoms. Around these atoms there are distorted six-coordinated YO6 octa­hedra and seven-coordinated YO7 penta­gonal bipyramids. The YO7 polyhedra are linked together, sharing their edges along a surface parallel to ab, forming a sheet. Each of these parallel sheets is inter­connected by means of GeO4 tetra­hedra, sharing an edge (or vertex) on one side and a vertex (or edge) on the other adjacent side. Parallel sheets of YO7 polyhedra are also inter­connected by undulating chains of YO6 octa­hedra along the c axis. These octa­hedra are joined together, sharing a common edge, to form the chain and share edges with the YO7 polyhedra of the sheets.

Related literature

For the isotypic structure of Dy2GeO5, see: Brixner et al. (1985 [triangle]). Different synthesis methods have been reported for this compound, including preparation by conventional r.f. magnetron sputtering (Minami et al., 2003 [triangle]), solid-state reactions at high temperatures (Zhao et al., 2003 [triangle]), MOCVD and LSMCD (Natori et al., 2004 [triangle]). For bond-valence parameters, see: Brese & O’Keeffe (1991 [triangle]), and for the bond-valence model, see: Brown (1981 [triangle], 1992 [triangle]). For oxide phosphors, see: Minami et al. (2001 [triangle], 2002 [triangle], 2004 [triangle]). Data used to model the second phase present in the reaction product, Y2Ge2O7, were taken from Redhammer et al. (2007 [triangle]). For related literature on technological applications, see: Fei et al. (2003 [triangle]).

Experimental

Crystal data

  • Y2GeO5
  • M r = 330.43
  • Monoclinic, An external file that holds a picture, illustration, etc.
Object name is e-65-00i60-efi1.jpg
  • a = 10.4706 (2) Å
  • b = 6.8292 (1) Å
  • c = 12.8795 (2) Å
  • β = 101.750 (3)°
  • V = 901.66 (3) Å3
  • Z = 8
  • Cu Kα radiation
  • T = 300 K
  • Specimen shape: flat sheet
  • 20 × 20 × 0.2 mm
  • Specimen prepared at 1443 K
  • Particle morphology: spherical, white

Data collection

  • Bruker Advance D8 diffractometer
  • Specimen mounting: packed powder sample container
  • Specimen mounted in reflection mode
  • Scan method: step
  • min = 8.0, 2θmax = 80.0°
  • Increment in 2θ = 0.02°

Refinement

  • R p = 0.053
  • R wp = 0.069
  • R exp = 0.024
  • S = 2.90
  • Wavelength of incident radiation: 1.540560 Å
  • Profile function: pseudo-Voigt modified by Thompson et al. (1987 [triangle])
  • 582 reflections
  • 105 parameters

Data collection: DIFFRAC/AT (Siemens, 1993 [triangle]); cell refinement: DICVOL91 (Boultif & Louëer 1991 [triangle]); data reduction: FULLPROF (Rodríguez-Carvajal, 2006 [triangle]); method used to solve structure: coordinates taken from an isotypic compound (Brixner et al., 1985 [triangle]); program(s) used to refine structure: FULLPROF; molecular graphics: ATOMS (Dowty, 2000 [triangle]); software used to prepare material for publication: FULLPROF.

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536809026579/br2110sup1.cif

Rietveld powder data: contains datablocks I. DOI: 10.1107/S1600536809026579/br2110Isup2.rtv

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Acknowledgments

The authors acknowledge the collaboration of Manuel Aguilar Franco for performing the conventional X-ray diffraction measurements, and projects CONACyT SEP-2007–81700.

supplementary crystallographic information

Comment

Field emission display (FED) constitutes the next generation of information display devices. Its advantages include portable size with low power consumption, broad viewing angle, and wide operating-temperature range among others (Zhao et al., 2003). New multicomponent oxide phosphor, Mn-activated Y2O3—GeO2, is promising as the thin-film emitting layer for thin-film electroluminescent (TFEL) devices (Minami et al., 2001). The oxide phosphor for use in those electroluminescent devices is formed from yttrium oxide and a transition metal as an activator, or from Y—Ge—O oxide and one metallic element to form M:Y2GeO5 where M is a metal (Minami et al., 2002; Minami et al., 2004). Other reported use for Y2GeO5 consists in piezoelectric ceramics in the form of films which include a complex oxide material having an oxygen octahedral structure and a paraelectric material having a catalytic effect for the complex oxide material in a mixed state. Paraelectric material could be a layered compound having an oxygen tetrahedral structure which includes one compound with the form MSiOx (M=metal) and Y2GeO5 (Natori et al., 2004). Fig. 1a show a fragment of the crystal structure of Y2GeO5 along the ab plane in which YO7 polyhedra share common edges forming a mesh. These YO7 polyhedra are represented as medium slate blue. Over the mesh, there are isolated GeO4 tetrahedra, which are represented in yellow in Fig. 1a. Each one of these parallel sheets are interconnected by means of GeO4 tetrahedra, sharing an edge (or vertix) in one side and a vertix (or edge) in the other adjacent side respectively as can be seen in Fig. 1b. Undulating chains of YO6 octahedra along the c axis are represented in gray in Fig. 1c in which the YO7 polyhedra were not represented in order lo clarify this feature of the arrangement. The chains of YO6 octahedra also interconnect the parallel sheets of YO7 polyhedra, as can be see in the unit cell of Y2GeO5 represented in Fig. 1d. Bond valence calculations were made using the recommended bond-valence parameters for oxides published by Brese & O'Keeffe (1991). Bond valence sum (BVS) around six-coordinated Y1, seven-coordinated Y2, and Ge give the values of 3.03, 2.76 and 4.08 respectively, being the first and the last closer to the values of +3 and +4 expected for the yttrium and germanium atoms respectively. The second value of 2.76 was first interpreted as stretched bonds around Y2 exist, but this suggestion was withdrawn because there is no compressed cation in the unit cell capable to balance the supposed stretched bonds around Y2, as it is established in the Brown's bond valence model (Brown, 1981) for evaluating the existence of stresses in the crystal. In fact, calculating the so called Global Instability Index, which is obtained as the root mean square of the bond-valence sum deviation for all the N atoms present in the asymmetric unit (Brown, 1992) a value of 0.06 was obtained suggesting no strain. This is a remarkably low value for a Rietveld refinement (for a well refined and unstrained structure this is less than 0.1). Then, the low value of the bond valence sum around Y2 is well within normal limits for a Rietveld refinment where larger deviations are typically found.

Experimental

The reactive mixture was prepared from Y2O3 (Aldrich.99.99%) and GeO2 (CERAC 99.999%) according to the stoichiometric proportions desired. The mixture was first powdered using an agate mortar; and then was heated in air in a tube furnace at 1373 K for 5 days with intermediate regrindings. A second thermal treatment at 1443 K for two days was applied. The characterization of the bulk material by conventional X-ray powder diffraction data indicated the presence of a well crystallized phase showing reflections that match with the isostructural phase DyGeO5 (PDF 01–078–0478). Very small amount of a secondary phase Y2Ge2O7 (PDF 38–288) was identified.

Refinement

The starting structural parameters for perform a Rietveld refinement of the Y2GeO5 phase were taken from the isostructural data reported for Dy2GeO5 (ICSD 61373) by Brixner et al. (1985). For modeling the second phase Y2Ge2O7 (ICSD 240989), the data were those reported by Redhammer et al. (2007). The following parameters were refined: zero point and scale factors, cell parameters, half-width profile parameters, overall temperature factors, atomic coordinates, and asymmetries. For the Y2Ge2O7 phase the atomic coordinates were fixed to their starting values. The final Rietveld refinement of conventional diffraction pattern is shown in Fig. 2.

Figures

Fig. 1.
(a) View of a YO7 layer in the Y2GeO5 structure (ab projection). YO7 polyhedra are represented in medium slate blue while GeO4 tetrahedra are represented in yellow. (b) View of the Y2GeO5 structure (ac projection). The layers formed by YO7 polyhedra are ...
Fig. 2.
Rietveld refinement for X-ray diffraction data. Observed (crosses), calculated (solid line) and difference (bottom trace) plots are represented; vertical marks correspond to the allowed Bragg reflections for Y2GeO5 (top) and Y2Ge2O7 (bottom) as secondary ...

Crystal data

Y2GeO5Z = 8
Mr = 330.43F(000) = 1200
Monoclinic, I2/aDx = 4.868 Mg m3
Hall symbol: -I 2yaCu Kα radiation, λ = 1.540560 Å
a = 10.4706 (2) ÅT = 300 K
b = 6.8292 (1) ÅParticle morphology: spherical
c = 12.8795 (2) Åwhite
β = 101.750 (3)°flat sheet, 20 × 20 mm
V = 901.66 (3) Å3Specimen preparation: Prepared at 1443 K

Data collection

Bruker Advance D8 diffractometerData collection mode: reflection
Radiation source: sealed X-ray tube, Cu KαScan method: step
graphitemin = 7.98°, 2θmax = 80.00°, 2θstep = 0.02°
Specimen mounting: packed powder sample container

Refinement

Least-squares matrix: full with fixed elements per cycleProfile function: pseudo-Voigt modified by Thompson et al. (1987)
Rp = 0.053105 parameters
Rwp = 0.069Weighting scheme based on measured s.u.'s
Rexp = 0.024(Δ/σ)max = 0.02
χ2 = 8.410Background function: The background was refined first by mean of a linear interpolation between 55 background points with adjustable heights. At the end of the refinement, the values for all of these heights of the background were fixed.
3704 data points

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2)

xyzUiso*/Ueq
Y10.3011 (2)0.6277 (2)0.6380 (1)0.0096 (7)
Y20.0708 (2)0.2567 (3)0.5355 (1)0.0090 (7)
Ge10.6236 (2)0.5933 (3)0.8155 (2)0.0121 (9)
O10.1210 (9)0.604 (1)0.5178 (8)0.009 (2)
O20.2950 (9)0.298 (1)0.6172 (7)0.009 (2)
O30.5212 (9)0.654 (1)0.6971 (8)0.009 (2)
O40.551 (1)−0.006 (1)0.4155 (8)0.009 (2)
O50.2412 (8)0.572 (1)0.7926 (8)0.009 (2)

Geometric parameters (Å, °)

Y1—O12.189 (8)Y2—O2i2.655 (10)
Y1—O1i2.321 (10)Y2—O3iv2.327 (10)
Y1—O22.270 (8)Y2—O4i2.358 (9)
Y1—O32.283 (8)Y2—O4v2.287 (9)
Y1—O52.238 (10)Ge1—O2vi1.767 (8)
Y1—O5ii2.316 (8)Ge1—O31.727 (8)
Y2—O12.447 (8)Ge1—O4vii1.732 (10)
Y2—O1iii2.203 (8)Ge1—O5viii1.739 (9)
Y2—O22.386 (8)
Y1—O1—Y1ix53.6 (2)Y1—O2—Y2xiii118.8 (3)
Y1—O1—Y2x128.7 (3)Y2xii—O2—Y2xiii61.19 (6)
Y1ix—O1—Y2x78.64 (6)Y1—O3—Y2xiv110.7 (3)
Y1ix—O1—Y2xi90.44 (7)Y2xv—O4—Y2xvi124.20 (7)
Y2x—O1—Y2xi157.05 (6)Y1—O5—Y1xvii89.8 (2)
Y1—O2—Y2xii97.4 (2)

Symmetry codes: (i) −x+1/2, y, −z+1; (ii) −x+1/2, −y+3/2, −z+3/2; (iii) −x, −y+1, −z+1; (iv) x−1/2, −y+1, z; (v) x−1/2, −y, z; (vi) −x+1, y+1/2, −z+3/2; (vii) x, −y+1/2, z+1/2; (viii) x+1/2, −y+1, z; (ix) −x+3/2, y, −z+1; (x) −x, −y, −z; (xi) x+1/2, −y+1, z+1; (xii) −x+1/2, y, −z; (xiii) −x+1, −y, −z+1; (xiv) −x+3/2, y+1, −z; (xv) x+1, y, z+1; (xvi) −x+3/2, y, −z; (xvii) −x+3/2, y+2, −z+2.

Footnotes

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: BR2110).

References

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