inorganic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

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ISSN: 2056-9890

aCentro de Física Aplicada y Tecnología Avanzada, Universidad Nacional Autónoma de México, AP 1-1010, Queretaro, Qro. 76000, Mexico, and bInstituto de Física, Universidad Nacional Autónoma de México, AP 20-364, 01000 México DF, Mexico
*Correspondence e-mail: emrivera@fata.unam.mx

(Received 25 June 2009; accepted 8 July 2009; online 15 July 2009)

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[Brixner, L. H., Calabrese, J. C. & Chen, H.-Y. (1985). J. Less-Common Met. 110, 397-410.]). Different synthesis methods have been reported for this compound, including preparation by conventional r.f. magnetron sputtering (Minami et al., 2003[Minami, T., Kobayashi, Y., Miyata, T. & Yamazaki, M. (2003). Thin Solid Films, 425, 35-40.]), solid-state reactions at high temperatures (Zhao et al., 2003[Zhao, F., Guo, P., Li, G., Liao, F., Tian, S. & Jing, X. (2003). Mater. Res. Bull. 38, 931-940.]), MOCVD and LSMCD (Natori et al., 2004[Natori, E., Kijima, T., Furuyama, K. & Tasaki, Y. (2004). Eur. Patent No. EP20020738688.]). For bond-valence parameters, see: Brese & O'Keeffe (1991[Brese, N. E. & O'Keeffe, M. (1991). Acta Cryst. B47, 192-197.]), and for the bond-valence model, see: Brown (1981[Brown, I. D. (1981). Structure and Bonding in Crystals, Vol. 2, edited by M. O'Keefe & A. Navrotsky, pp. 1-30. New York: Academic Press.], 1992[Brown, I. D. (1992). Z. Kristallogr. 199, 255-272.]). For oxide phosphors, see: Minami et al. (2001[Minami, T., Yamazaki, M., Miyata, T. & Shirai, T. (2001). Jpn J. Appl. Phys. 40, L864-L866.], 2002[Minami, T., Miyata, T., Ueno, T. & Urano, Y. (2002). US Patent No. 2002/0047515 Al.], 2004[Minami, T., Miyata, T., Ueno, T. & Urano, Y. (2004). US Patent No. 6707249 B2.]). Data used to model the second phase present in the reaction product, Y2Ge2O7, were taken from Redhammer et al. (2007[Redhammer, G. J., Roth, G. & Amthauer, G. (2007). Acta Cryst. C63, i93-i95.]). For related literature on technological applications, see: Fei et al. (2003[Fei, Z., Peimin, G., Guobao, L., Fuhui, L., Shujian, T. & Xiping, J. (2003). Mater. Res. Bull. 38, 931-940.]).

Experimental

Crystal data
  • Y2GeO5

  • Mr = 330.43

  • Monoclinic, I 2/a

  • 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

  • 2θmin = 8.0, 2θmax = 80.0°

  • Increment in 2θ = 0.02°

Refinement
  • Rp = 0.053

  • Rwp = 0.069

  • Rexp = 0.024

  • S = 2.90

  • Wavelength of incident radiation: 1.540560 Å

  • Profile function: pseudo-Voigt modified by Thompson et al. (1987[Thompson, P., Cox, D. E. & Hastings, J. B. (1987). J. Appl. Cryst. 20, 79-83.])

  • 582 reflections

  • 105 parameters

Data collection: DIFFRAC/AT (Siemens, 1993[Siemens (1993). DIFFRAC/AT. Siemens Analytical X-ray Instruments Inc., Madison, Wisconsin, USA.]); cell refinement: DICVOL91 (Boultif & Louëer 1991[Boultif, A. & Louër, D. (1991). J. Appl. Cryst. 24, 987-993.]); data reduction: FULLPROF (Rodríguez-Carvajal, 2006[Rodríguez-Carvajal, J. (2006). FULLPROF. URL: http://www.ill.eu/sites/fullprof/ php/reference.html.]); method used to solve structure: coordinates taken from an isotypic compound (Brixner et al., 1985[Brixner, L. H., Calabrese, J. C. & Chen, H.-Y. (1985). J. Less-Common Met. 110, 397-410.]); program(s) used to refine structure: FULLPROF; molecular graphics: ATOMS (Dowty, 2000[Dowty, E. (2000). ATOMS for Windows. Shape Software, Kingsport, Tennessee, USA.]); software used to prepare material for publication: FULLPROF.

Supporting information


Comment top

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.

Related literature top

For a related structure, see: Brixner et al. (1985). There are different synthesis methods reported in literature for this compound, including preparation by conventional r.f. magnetron sputtering (Minami et al., 2003), solid-state reactions at high temperatures (Zhao et al., 2003), MOCVD and LSMCD (Natori et al., 2004). For related literature, see: Brese & O'Keeffe (1991); Brown (1981, 1992); Dowty (2000); Fei et al. (2003); Minami et al. (2001, 2002, 2004); Redhammer et al. (2007).

Experimental top

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 top

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.

Computing details top

Data collection: DIFFRAC/AT (Siemens, 1993); cell refinement: DICVOL91 (Boultif & Lou1"er 1991); data reduction: FULLPROF (Rodríguez-Carvajal, 2006); program(s) used to solve structure: coordinates were taken from isotypic compound; program(s) used to refine structure: FULLPROF (Rodríguez-Carvajal, 2006); molecular graphics: ATOMS (Dowty, 2000); software used to prepare material for publication: ATOMS (Dowty, 2000).

Figures top
[Figure 1] 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 linked together by GeO4 tetrahedra. (c) Chains of YO6 octahedra (in gray) undulating along the c axis sharing common edges and linked with other chains by mean of GeO4 tetrahedra. (d) Unit cell for Y2GeO5 structure.
[Figure 2] 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 phase.
yttrium germanium pentaoxide top
Crystal data top
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 top
Bruker Advance D8
diffractometer
Data collection mode: reflection
Radiation source: sealed X-ray tube, Cu KαScan method: step
Graphite monochromator2θmin = 7.979°, 2θmax = 80.002°, 2θstep = 0.020°
Specimen mounting: packed powder sample container
Refinement top
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
Crystal data top
Y2GeO5β = 101.750 (3)°
Mr = 330.43V = 901.66 (3) Å3
Monoclinic, I2/aZ = 8
a = 10.4706 (2) ÅCu Kα radiation, λ = 1.540560 Å
b = 6.8292 (1) ÅT = 300 K
c = 12.8795 (2) Åflat sheet, 20 × 20 mm
Data collection top
Bruker Advance D8
diffractometer
Scan method: step
Specimen mounting: packed powder sample container2θmin = 7.979°, 2θmax = 80.002°, 2θstep = 0.020°
Data collection mode: reflection
Refinement top
Rp = 0.053χ2 = 8.410
Rwp = 0.0693704 data points
Rexp = 0.024105 parameters
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
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, º) top
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) x1/2, y+1, z; (v) x1/2, 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.

Experimental details

Crystal data
Chemical formulaY2GeO5
Mr330.43
Crystal system, space groupMonoclinic, I2/a
Temperature (K)300
a, b, c (Å)10.4706 (2), 6.8292 (1), 12.8795 (2)
β (°) 101.750 (3)
V3)901.66 (3)
Z8
Radiation typeCu Kα, λ = 1.540560 Å
Specimen shape, size (mm)Flat sheet, 20 × 20
Data collection
DiffractometerBruker Advance D8
diffractometer
Specimen mountingPacked powder sample container
Data collection modeReflection
Scan methodStep
2θ values (°)2θmin = 7.979 2θmax = 80.002 2θstep = 0.020
Refinement
R factors and goodness of fitRp = 0.053, Rwp = 0.069, Rexp = 0.024, χ2 = 8.410
No. of data points3704
No. of parameters105
No. of restraints?

Computer programs: DIFFRAC/AT (Siemens, 1993), DICVOL91 (Boultif & Lou1"er 1991), FULLPROF (Rodríguez-Carvajal, 2006), coordinates were taken from isotypic compound, ATOMS (Dowty, 2000).

 

Acknowledgements

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

References

First citationBoultif, A. & Louër, D. (1991). J. Appl. Cryst. 24, 987–993.  CrossRef CAS Web of Science IUCr Journals Google Scholar
First citationBrese, N. E. & O'Keeffe, M. (1991). Acta Cryst. B47, 192–197.  CrossRef CAS Web of Science IUCr Journals Google Scholar
First citationBrixner, L. H., Calabrese, J. C. & Chen, H.-Y. (1985). J. Less-Common Met. 110, 397-410.  CrossRef CAS Web of Science Google Scholar
First citationBrown, I. D. (1981). Structure and Bonding in Crystals, Vol. 2, edited by M. O'Keefe & A. Navrotsky, pp. 1–30. New York: Academic Press.  Google Scholar
First citationBrown, I. D. (1992). Z. Kristallogr. 199, 255–272.  CrossRef CAS Web of Science Google Scholar
First citationDowty, E. (2000). ATOMS for Windows. Shape Software, Kingsport, Tennessee, USA.  Google Scholar
First citationFei, Z., Peimin, G., Guobao, L., Fuhui, L., Shujian, T. & Xiping, J. (2003). Mater. Res. Bull. 38, 931–940.  Google Scholar
First citationMinami, T., Kobayashi, Y., Miyata, T. & Yamazaki, M. (2003). Thin Solid Films, 425, 35–40.  Web of Science CrossRef CAS Google Scholar
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First citationMinami, T., Miyata, T., Ueno, T. & Urano, Y. (2004). US Patent No. 6707249 B2.  Google Scholar
First citationMinami, T., Yamazaki, M., Miyata, T. & Shirai, T. (2001). Jpn J. Appl. Phys. 40, L864–L866.  Web of Science CrossRef CAS Google Scholar
First citationNatori, E., Kijima, T., Furuyama, K. & Tasaki, Y. (2004). Eur. Patent No. EP20020738688.  Google Scholar
First citationRedhammer, G. J., Roth, G. & Amthauer, G. (2007). Acta Cryst. C63, i93–i95.  Web of Science CrossRef IUCr Journals Google Scholar
First citationRodríguez-Carvajal, J. (2006). FULLPROF. URL: http://www.ill.eu/sites/fullprof/ php/reference.html.  Google Scholar
First citationSiemens (1993). DIFFRAC/AT. Siemens Analytical X-ray Instruments Inc., Madison, Wisconsin, USA.  Google Scholar
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First citationZhao, F., Guo, P., Li, G., Liao, F., Tian, S. & Jing, X. (2003). Mater. Res. Bull. 38, 931–940.  Web of Science CrossRef CAS Google Scholar

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ISSN: 2056-9890
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