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

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CHEMISTRY
ISSN: 2053-2296

Tetragonal CeNbO4 at 1073 K in air and in vacuo

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aDepartment of Materials, Imperial College London, Prince Consort Road, London SW7 2BP, England
*Correspondence e-mail: s.skinner@imperial.ac.uk

(Received 6 November 2003; accepted 10 February 2004; online 20 March 2004)

The structure of the high-temperature scheelite-type polymorph of cerium niobium tetraoxide, CeNbO4, has been determined using time-of-flight neutron powder diffraction data collected both in situ at 1073 K in air and in vacuo. In both cases, the structure was found to be tetragonal, with I41/a symmetry and without any significant deviation from the stoichiometric composition.

Comment

Several authors have investigated the structure of CeNbO4, particularly under ambient conditions (Negas et al., 1977[Negas, T., Roth, R. S., McDaniel, C. L., Parker, H. S. & Olson, C. D. (1977). Mater. Res. Bull. 12, 1161-1172.]; Roth et al., 1977[Roth, R. S., Negas, T., Parker, H. S., Minor, D. B. & Jones, C. (1977). Mater. Res. Bull. 12, 1173-1182.], 1978[Roth, R. S., Negas, T., Parker, H. S., Minor, D. B., Olson, C. D. & Skarda, C. (1978). The Rare Earths in Modern Science and Technology, edited by G. J. McCarthy & J. J. Rhyne, pp. 163-171. New York/London: Plenum Press.]; Cava et al., 1978[Cava, R. J., Negas, T., Roth, R. S., Parker, H. S., Minor, D. B. & Olson, C. D. (1978). The Rare Earths in Modern Science and Technology, edited by G. J. McCarthy & J. J. Rhyne, pp. 181-187. New York/London: Plenum Press.]; Santoro et al., 1980[Santoro, A., Marezio, M., Roth, R. S. & Minor, D. (1980). J. Solid State Chem. 35, 167-175.]; Thompson et al., 1999[Thompson, J. G., Withers, R. L. & Brink, F. J. (1999). J. Solid State Chem. 143, 122-131.]), and only recently has there been any attempt to characterize the structure at elevated temperatures, with one recent report of an in situ characterization of phase transformations on heating that presented minimal structural information (Skinner & Kang, 2003[Skinner, S. J. & Kang, Y. (2003). Solid State Sci. 5, 1475-1479.]). The recent interest in this material has stemmed from the possible incorporation of oxy­gen interstitials that would make this material amenable to oxide ion conducting applications, such as solid electrolytes, sensors and separation membranes. The purpose of this study was to investigate the structure of the high-temperature polymorph under both static air and vacuum conditions in order to gather information regarding the likely flexibility of oxy­gen stoichiometry in CeNbO4.

The low-temperature polymorph of CeNbO4 has been described previously as a monoclinic distortion of the tetragonal scheelite structure, adopting a fergusonite-type structure (Santoro et al., 1980[Santoro, A., Marezio, M., Roth, R. S. & Minor, D. (1980). J. Solid State Chem. 35, 167-175.]; Thompson et al., 1999[Thompson, J. G., Withers, R. L. & Brink, F. J. (1999). J. Solid State Chem. 143, 122-131.]). It was also predicted that CeNbO4 will undergo oxidation on heating in air and a structural transition on heating above 847 K (Gingerich & Blair, 1964[Gingerich, K. A. & Blair, H. E. (1964). Adv. X-ray Anal. 7, 22-30.]; Negas et al., 1977[Negas, T., Roth, R. S., McDaniel, C. L., Parker, H. S. & Olson, C. D. (1977). Mater. Res. Bull. 12, 1161-1172.]; Roth et al., 1977[Roth, R. S., Negas, T., Parker, H. S., Minor, D. B. & Jones, C. (1977). Mater. Res. Bull. 12, 1173-1182.]; Cava et al., 1978[Cava, R. J., Negas, T., Roth, R. S., Parker, H. S., Minor, D. B. & Olson, C. D. (1978). The Rare Earths in Modern Science and Technology, edited by G. J. McCarthy & J. J. Rhyne, pp. 181-187. New York/London: Plenum Press.]). Recently, in situ measurements have raised questions about the nature of these oxidation and transformation processes (Skinner & Kang, 2003[Skinner, S. J. & Kang, Y. (2003). Solid State Sci. 5, 1475-1479.]). However, until the present work, there has been no determination of the structure of the tetragonal form of CeNbO4. From our initial X-ray diffraction results, it was immediately apparent that the data recorded at 1073 K conformed to a scheelite-type structure. As a starting model for the Rietveld refinement of the neutron powder diffraction data, the structure of scheelite (CaWO4) was therefore used [space group I41/a; alternate setting with origin at (0, [1\over4], [1\over8]); the Ce and Nb atoms in the 4b and 4a positions, respectively, and the O atom in the 16f position (Hazen et al., 1985[Hazen, R. M., Finger, L. W. & Mariathasan, J. W. E. (1985). J. Phys. Chem. Solids, 46, 253-263.])]. The refinements were carried out using the GSAS package (Larson & Von Dreele, 1994[Larson, A. C. & Von Dreele, R. B. (1994). GSAS. Report No. LAUR 86-748. Los Alamos National Laboratory, New Mexico, USA.]) and provided good fits to the 90° and backscattered neutron diffraction data collected in air and in vacuo (10−3 Pa) (Fig. 1[link]).

In common with other scheelite-type compounds, the Ce atoms in CeNbO4 are in an eightfold coordination environment, with two distinct bond lengths, while the Nb environment is tetrahedral, with equal Nb—O bonds (Fig. 2[link]). The slightly larger unit-cell volume of the sample heated in static air is associated with slightly longer Nb—O and Ce—O distances (Tables 1[link] and 2[link]). The distorted tetrahedral environment for the Nb atom, with O—Nb—O angles of 106.476 (19) and 115.64 (4)°, is comparable to that in isostructural LaNbO4 (David, 1983[David, W. I. F. (1983). Mater. Res. Bull. 18, 749-756.]; Machida et al., 1995[Machida, M., Kido, J., Kobagashi, T., Fukui, S., Koyano, N. & Suemone, Y. (1995). Annual Reports 25-32. Kyoto University Research Reactor Institute, Japan.]). The transition temperature in CeNbO4 is significantly higher than that in LaNbO4 (773 K).

From the results of both refinements and from Fourier difference maps, it is apparent that the high-temperature CeNbO4 polymorph is fully stoichiometric, and there is no evidence to suggest that heating it in air introduced any interstitial oxy­gen. Because the sample was heated in situ while packed in a vanadium can, it is conceivable that limited oxidation occurred at the surface only. Hence, it would be desirable either to perform a series of measurements at one temperature over a period of time to enable the study of possible oxy­gen incorporation into CeNbO4 or to oxidize a sample before carrying out a set of measurements at temperatures up to 1073 K, allowing any oxy­gen stoichiometry variations on heating to be investigated.

[Figure 1]
Figure 1
(a) A Rietveld plot for the refinement of backscattered neutron diffraction data in vacuo. The experimental and calculated profiles are represented by crosses and a full line, respectively. The difference plot is shown underneath and tick marks indicate the positions of Bragg reflections. (b) A Rietveld plot for the refinement of the 90° bank neutron diffraction data in air. Profiles are drawn as in (a).
[Figure 2]
Figure 2
A representation of the tetragonal scheelite-type structure of CeNbO4, showing the Nb and Ce coordination environments. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry code: (i) x + [1\over 2], y + [1\over 2], [{1 \over 2}] − z.]

Experimental

Samples were produced through the mixing of CeO2 (99.9%, Sigma Aldrich) and Nb2O5 (99.99%, Sigma Aldrich) in an agate mortar and pestle. These starting materials were mixed thoroughly under acetone and allowed to dry in air before the stoichiometric mixture was transferred to an alumina crucible for heat treatment. The mixture was prefired at 1273 K for 10 h and allowed to cool. After further mixing, the material was heated at 1673 K for 16 h and quenched. This procedure produced a bright-green material. X-ray powder diffraction data were recorded on a Philips PW1700 series diffrac­tometer using Cu Kα1 radiation and a graphite crystal as secondary monochromator. Neutron powder diffraction data were collected from 6 g samples contained in vanadium cans on the POLARIS diffractometer using both 90° and backscatter detectors at ISIS, CCLRC Rutherford Appleton Laboratory, Oxfordshire, England. Each data set was collected over a period of 90 min, and then normalized and corrected in the usual way. Two separate samples were ex­amined during these measurements. The first sample was heated in situ under vacuum with data recorded on heating and cooling. For the second sample, the same in situ heating regime was used but the can was exposed to static air. The data were collected at 296 K, every 100 K from 473 to 973 K, and every 50 K from 973 to 1123 K. On cooling, data were recorded at 1023, 823 and 623 K. Only the data recorded at 1073 K from the samples heated in air and in vacuo are included here.

In vacuo

Crystal data
  • CeNbO4

  • Mr = 297.02

  • Tetragonal, I41/a, origin choice 2 at (0, [1\over 4], [1\over 8]) from [\overline 4]

  • a = 5.37119 (8) Å

  • c = 11.58104 (18) Å

  • V = 334.109 (9) Å3

  • Z = 4

  • Dx = 5.905 Mg m−3

  • Neutron radiation

  • λ = 0.1–6.0 Å

  • T = 1073 K

  • Light green

Data collection
  • Polaris diffractometer at ISIS (England)

  • Specimen mounting: 6 mm diameter vanadium can

  • 2884 independent reflections

Refinement
  • Refinement on F2

  • Rp = 0.0196

  • Rwp = 0.0116

  • Rexp = 0.0065

  • S = 1.81

  • Profile function: exponential pseudo-Voigt convolution

  • 2884 reflections

  • 49 parameters

  • (Δ/σ)max = 0.02

Table 1
Selected interatomic distances (Å) for vacuum data

Ce⋯Ce 3.94904 (4)
Ce—Oii 2.5100 (6)
Ce—Oiii 2.4847 (6)
Nb—O 1.8537 (5)
Symmetry codes: (ii) -x,1-y,1-z; (iii) [{\script{1\over 2}}-x,1-y,{\script{1\over 2}}+z].

In air

Crystal data
  • CeNbO4

  • Mr = 297.02

  • Tetragonal, I41/a, origin choice 2 at (0, [1\over 4], [1\over 8]) from [\overline 4]

  • a = 5.37692 (8) Å

  • c = 11.59514 (18) Å

  • V = 335.230 (8) Å3

  • Z = 4

  • Dx = 5.835 Mg m−3

  • Neutron radiation

  • λ = 0.1–6.0 Å

  • T = 1073 K

  • Light green

Data collection
  • Polaris diffractometer at ISIS (England)

  • Specimen mounting: 6 mm diameter vanadium can

  • 2884 independent reflections

Refinement
  • Refinement on F2

  • Rp = 0.0203

  • Rwp = 0.0118

  • Rexp = 0.0065

  • S = 1.83

  • Profile function: exponential pseudo-Voigt convolution

  • 2884 reflections

  • 49 parameters

  • (Δ/σ)max = 0.03

Table 2
Selected interatomic distances (Å) for air data

Ce⋯Ceiv 3.95358 (4)
Ce—Oii 2.5128 (6)
Ce—Oiii 2.4882 (6)
Nb—O 1.8553 (5)
Symmetry codes: (ii) -x,1-y,1-z; (iii) [{\script{1\over 2}}-x,1-y,{\script{1\over 2}}+z]; (iv) [-{\script{1\over 4}}-y,{\script{1\over 4}}+x,{\script{1\over 4}}+z].

Initial refinement cycles showed no significant deviation from stoichiometry, and therefore the occupancies of the Ce- and Nb-atom sites were fixed to unity in the final cycles for both the air and the vacuum data sets. The occupancy of the O-atom site was allowed to vary but did not deviate significantly from unity either. Fourier difference maps indicated no significant residual scattering density within the unit cell, with maxima of 0.49 Å−3 at (0.2465, 0.5004, 0.1234) for the vacuum data and 0.46 Å−3 at (0.1545, 0.9652, 0.1803) for the air data.

For both compounds, data ecollection: Polaris instrument control program; cell refinement: GSAS (Larson & Von Dreele, 1994[Larson, A. C. & Von Dreele, R. B. (1994). GSAS. Report No. LAUR 86-748. Los Alamos National Laboratory, New Mexico, USA.]); program(s) used to solve structure: GSAS; program(s) used to refine structure: GSAS; molecular graphics: GRETEP (Laugier & Bochu, 2004[Laugier, J. & Bochu, B., (2004). GRETEP. LMPG, Grenoble, France.]) and POVRAY (URL: www.povray.org).

Supporting information


Comment top

Several authors have investigated the structure of CeNbO4, particularly under ambient conditions (Negas et al., 1977; Roth et al., 1977; Roth et al., 1978; Cava et al., 1978; Santoro et al., 1980; Thompson et al., 1999) and only recently has there been any attempt to characterize the structure at elevated temperatures, with one recent report of an in situ characterization of phase transformations on heating that presented minimal structural information (Skinner & Kang, 2003). The recent interest in this material has stemmed from the possible incorporation of oxygen interstitials that would make this material amenable to oxide ion conducting applications, such as solid electrolytes, sensors and separation membranes. The purpose of this study was to investigate the structure of the high-temperature polymorph under both static air and vacuum conditions in oreder to gather information regarding the likely flexibility of oxygen stoichiometry in CeNbO4.

The low-temperature polymorph of CeNbO4 has previously been described as a monoclinic distortion of the tetragonal scheelite structure, adopting a fergusonite-type structure (Santoro et al., 1980; Thompson et al., 1999). Previously, it was also predicted that CeNbO4 will undergo oxidation upon heating in air and a structural transition upon heating above 847 K (Gingerich & Blair, 1964; Cava et al., 1976; Negas et al., 1977; Roth et al., 1977). Recently, in situ measurements have raised questions about the nature of these oxidation and transformation processes (Skinner & Kang, 2003). However, until the present work, there has been no determination of the structure of the tetragonal form of CeNbO4. From our initial X-ray diffraction results, it was immediately apparent that the data recorded at 1073 K conformed to a scheelite-type structure. As a starting model for the Rietveld refinement of the neutron powder diffraction data, the structure of scheelite (CaWO4) was therefore used [space group I41/a; alternate setting with origin at (0, 1/4, 1/8); the Ce and Nb atoms in the 4 b and 4a positions, respectively, and the O atom in the 16f position (Hazen et al., 1985)]. The refinements were carried out using the GSAS package (Larson & Von Dreele, 1994) and provided good fits to the 90° and backscattered neutron diffraction data collected in air and in vacuo (10−5 mbar) (Fig. 1).

In common with other scheelite-type compounds, the Ce atoms in CeNbO4 are in an eightfold coordination environment, with two distinct bond lengths, while the Nb environment is tetrahedral, with equal Nb—O bonds (Fig. 2). The slightly larger unit-cell volume of the sample heated in static air is associated with slightly longer Nb—O and Ce—O distances. The distorted tetrahedral environment for the Nbatom, with O—Nb—O angles of 106.476 (19) and 115.64 (4)°, is comparable to that in isostructural LaNbO4 (David, 1983; Machida et al., 1995). The transition temperature in CeNbO4 is significantly higher than in LaNbO4 (773 K).

From the results of both refinements and from Fourier difference maps, it is apparent that the high-temperature CeNbO4 polymorph is fully stoichiometric, and there is no evidence to suggest that heating it in air introduced any interstitial oxygen. Because the sample was heated in situ while packed in a vanadium can, it is conceivable that limited oxidation occurred at the surface only. Hence it would be desirable either to perform a series of measurements at one temperature over a period of time to enable the study of possible oxygen incorporation into CeNbO4 or to oxidize a sample before carrying out a set of measurements at temperatures up to 1073 K, allowing any oxygen stoichiometry variations on heating to be investigated.

Experimental top

Samples were produced through the mixing of CeO2 (99.9%, Sigma Aldrich) and Nb2O5 (99.99%, Sigma Aldrich) in an agate mortar and pestle. These starting materials were mixed thoroughly under acetone and allowed to dry in air before the stoichiometric mixture was transferred to an alumina crucible for heat treatment. The mixture was prefired at 1273 K for 10 h and allowed to cool. After further mixing, the material was heated at 1673 K for 16 h and quenched. This procedure produced a bright-green material. X-ray powder diffraction data were recorded on a Philips PW1700 series diffractometer using Cu Kα1 radiation and a graphite crystal as secondary monochromator. Neutron powder diffraction data were collected from 6 g samples contained in vanadium cans on the POLARIS diffractometer using both 90° and backscatter detectors at ISIS, CCLRC Rutherford Appleton Laboratory, Oxfordshire, England. Each dataset was collected over a period of 90 min, and then normalized and corrected in the usual way. Two separate samples were examined during these measurements. The first sample was heated in situ under vacuum with data recorded on heating and cooling. For the second sample, the same in situ heating regime was used but the can was exposed to static air. The data were collected at 296 K, every 100 K from 473 to 973 K, and every 50 K from 973 to 1123 K. On cooling, data were recorded at 1023, 823 and 623 K. Only the data recorded at 1073 K from the samples heated in air and in vacuo are included here.

Refinement top

Initial refinement cycles showed no significant deviation from stoichiometry, and therefore the occupancies of the Ce and Nb sites were fixed to unity in the final cycles for both the air and the vacuum data sets. The occupancy of the O site was allowed to vary but did not deviate significantly from unity either. Fourier difference maps indicated no significant residual scattering density within the unit cell, with maxima of 0.489 Å−3 at (0.2465 0.5004 0.1234) for the vacuum data and 0.459 Å−3 at (0.1545 0.9652 0.1803) for the air data.

Computing details top

For both compounds, program(s) used to solve structure: GSAS; program(s) used to refine structure: GSAS.

Figures top
[Figure 1] Fig. 1. (a) A Rietveld plot for the refinement of backscattered neutron diffraction data in vacuo. The experimental and calculated profiles are represented by crosses and a full line, respectively. The difference plot is shown underneath and tick marks indicate the positions of Bragg reflections. (b) A Rietveld plot for the refinement of the 90° bank neutron diffraction data in air. Profiles are drawn as in (a).
[Figure 2] Fig. 2. Representation of the tetragonal scheelite-type structure of CeNbO4, showing the Nb and Ce coordination environments. Displacement ellipsoids are drawn at the 50% probablity level. [Symmetry code: (i) x + 1/2, y + 1/2, 1/2 − z.]
(vacuum) cerium niobium tetraoxide top
Crystal data top
CeNbO4Z = 4
Mr = 297.02Dx = 5.905 Mg m3
Tetragonal, I41/a,originchoice2at0,1/4,1/8from4Neutron radiation
Hall symbol: -I 4aT = 1073 K
a = 5.37119 (8) Ålight green
c = 11.58104 (18) Å?, ? × ? × ? mm
V = 334.11 (1) Å3
Data collection top
Polaris
diffractometer at ISIS
2θfixed = 145o for backscatter detector (average)
Radiation source: spallation neutron sourceDistance from source to specimen: 12.0 m mm
Specimen mounting: 6 mm diameter vanadium canDistance from specimen to detector: 0.80 m for backscatter detector mm
Scan method: time of flight
Refinement top
Refinement on F24565 data points
Least-squares matrix: fullProfile function: exponential pseudo-Voigt convolution
Rp = 0.02049 parameters
Rwp = 0.012 1/Yi
Rexp = 0.007(Δ/σ)max = 0.02
χ2 = 3.276Background function: shifted Chebyschev
Crystal data top
CeNbO4V = 334.11 (1) Å3
Mr = 297.02Z = 4
Tetragonal, I41/a,originchoice2at0,1/4,1/8from4Neutron radiation
a = 5.37119 (8) ÅT = 1073 K
c = 11.58104 (18) Å?, ? × ? × ? mm
Data collection top
Polaris
diffractometer at ISIS
2θfixed = 145o for backscatter detector (average)
Specimen mounting: 6 mm diameter vanadium canDistance from source to specimen: 12.0 m mm
Scan method: time of flightDistance from specimen to detector: 0.80 m for backscatter detector mm
Refinement top
Rp = 0.020χ2 = 3.276
Rwp = 0.0124565 data points
Rexp = 0.00749 parameters
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Ce0.00.250.6250.0173 (5)
Nb0.00.250.1250.0174 (4)
O0.16181 (9)0.49329 (12)0.21018 (5)0.0304 (3)1.0000 (22)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ce0.0195 (4)0.0195 (4)0.0130 (6)000
Nb0.0140 (3)0.0140 (3)0.0241 (5)000
O0.0326 (3)0.0326 (3)0.0257 (3)0.0142 (4)0.0075 (3)0.0108 (2)
Geometric parameters (Å, º) top
Ce—Cei3.9490 (1)Ce—Oiii2.4847 (6)
Ce—Oii2.5100 (6)Nb—O1.8537 (5)
Oiv—Ce—Oiii73.03 (1)Oiii—Ce—Ovi133.21 (3)
Oiv—Ce—Oii125.33 (2)O—Nb—Oix106.45 (2)
Oiv—Ce—Ov75.51 (2)O—Nb—Ox115.70 (4)
Oiv—Ce—Ovi153.59 (3)Cexi—O—Cexii104.49 (2)
Oiv—Ce—Ovii80.98 (3)Cexi—O—Nb121.51 (3)
Oiv—Ce—Oviii69.29 (2)Cexii—O—Nb129.02 (2)
Oiii—Ce—Ov99.06 (1)
Symmetry codes: (i) x, y, z+1; (ii) x, y+1, z+1; (iii) x+1/2, y+1, z+1/2; (iv) y+3/4, x+1/4, z+1/4; (v) y3/4, x+3/4, z+3/4; (vi) x1/2, y1/2, z+1/2; (vii) y3/4, x+1/4, z+1/4; (viii) y+3/4, x1/4, z+3/4; (ix) y1/4, x+1/4, z+1/4; (x) x, y+1/2, z; (xi) x+1/2, y+1, z1/2; (xii) y1/4, x+3/4, z1/4.
(air) cerium niobium tetraoxide top
Crystal data top
CeNbO4Z = 4
Mr = 297.02Dx = 5.835 Mg m3
Tetragonal, I41/a,originchoice2at0,1/4,1/8from4Neutron radiation
Hall symbol: -I 4adT = 1073 K
a = 5.37692 (8) Ålight green
c = 11.59514 (18) Å?, ? × ? × ? mm
V = 335.23 (1) Å3
Data collection top
Polaris
diffractometer at ISIS
2θfixed = 145o for backscatter detector (average)
Radiation source: spallation neutron sourceDistance from source to specimen: 12.0 m mm
Specimen mounting: 6 mm diameter vanadium canDistance from specimen to detector: 0.80 m for backscatter detector mm
Scan method: time of flight
Refinement top
Refinement on F2Profile function: exponential pseudo-Voigt convolution
Least-squares matrix: full49 parameters
Rp = 0.0200 restraints
Rwp = 0.012 1/Yi
Rexp = 0.007(Δ/σ)max = 0.03
χ2 = 3.349Background function: shifted Chebyschev
4565 data points
Crystal data top
CeNbO4V = 335.23 (1) Å3
Mr = 297.02Z = 4
Tetragonal, I41/a,originchoice2at0,1/4,1/8from4Neutron radiation
a = 5.37692 (8) ÅT = 1073 K
c = 11.59514 (18) Å?, ? × ? × ? mm
Data collection top
Polaris
diffractometer at ISIS
2θfixed = 145o for backscatter detector (average)
Specimen mounting: 6 mm diameter vanadium canDistance from source to specimen: 12.0 m mm
Scan method: time of flightDistance from specimen to detector: 0.80 m for backscatter detector mm
Refinement top
Rp = 0.0204565 data points
Rwp = 0.01249 parameters
Rexp = 0.0070 restraints
χ2 = 3.349
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Ce0.00.250.6250.0169 (4)
Nb0.00.250.1250.0173 (3)
O0.16173 (9)0.49318 (12)0.21021 (5)0.0303 (3)0.993 (3)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ce0.0188 (4)0.0188 (4)0.0131 (7)000
Nb0.0139 (3)0.0139 (3)0.0244 (6)000
O0.0322 (4)0.0319 (3)0.0268 (3)0.0145 (4)0.0075 (3)0.0106 (3)
Geometric parameters (Å, º) top
Ce—Cei3.9536 (1)Ce—Oiii2.4882 (6)
Ce—Oii2.5128 (6)Nb—O1.8553 (5)
Oiv—Ce—Oiii73.03 (1)Oiii—Ce—Ovi133.20 (3)
Oiv—Ce—Oii125.32 (2)O—Nb—Oix106.47 (2)
Oiv—Ce—Ov75.53 (2)O—Nb—Ox115.64 (4)
Oiv—Ce—Ovi153.60 (3)Cexi—O—Cexii104.47 (2)
Oiv—Ce—Ovii80.99 (3)Cexi—O—Nb121.48 (3)
Oiv—Ce—Oviii69.27 (2)Cexii—O—Nb129.05 (2)
Oiii—Ce—Ov99.07 (1)
Symmetry codes: (i) y1/4, x+1/4, z+1/4; (ii) x, y+1, z+1; (iii) x+1/2, y+1, z+1/2; (iv) y+3/4, x+1/4, z+1/4; (v) y3/4, x+3/4, z+3/4; (vi) x1/2, y1/2, z+1/2; (vii) y3/4, x+1/4, z+1/4; (viii) y+3/4, x1/4, z+3/4; (ix) y1/4, x+1/4, z+1/4; (x) x, y+1/2, z; (xi) x+1/2, y+1, z1/2; (xii) y1/4, x+3/4, z1/4.

Experimental details

(vacuum)(air)
Crystal data
Chemical formulaCeNbO4CeNbO4
Mr297.02297.02
Crystal system, space groupTetragonal, I41/a,originchoice2at0,1/4,1/8from4Tetragonal, I41/a,originchoice2at0,1/4,1/8from4
Temperature (K)10731073
a, c (Å)5.37119 (8), 11.58104 (18)5.37692 (8), 11.59514 (18)
V3)334.11 (1)335.23 (1)
Z44
Radiation typeNeutronNeutron
Specimen shape, size (mm)?, ? × ? × ??, ? × ? × ?
Data collection
DiffractometerPolaris
diffractometer at ISIS
Polaris
diffractometer at ISIS
Specimen mounting6 mm diameter vanadium can6 mm diameter vanadium can
Data collection mode??
Scan methodTime of flightTime of flight
2θ values (°)2θfixed = 145o for backscatter detector (average)2θfixed = 145o for backscatter detector (average)
Distance from source to specimen (mm)12.0 m12.0 m
Distance from specimen to detector (mm)0.80 m for backscatter detector0.80 m for backscatter detector
Refinement
R factors and goodness of fitRp = 0.020, Rwp = 0.012, Rexp = 0.007, χ2 = 3.276Rp = 0.020, Rwp = 0.012, Rexp = 0.007, χ2 = 3.349
No. of data points45654565
No. of parameters4949
No. of restraints?0

Computer programs: GSAS.

Selected bond lengths (Å) for (vacuum) top
Ce—Oi2.5100 (6)Nb—O1.8537 (5)
Ce—Oii2.4847 (6)
Symmetry codes: (i) x, y+1, z+1; (ii) x+1/2, y+1, z+1/2.
Selected bond lengths (Å) for (air) top
Ce—Cei3.9536 (1)Ce—Oiii2.4882 (6)
Ce—Oii2.5128 (6)Nb—O1.8553 (5)
Symmetry codes: (i) y1/4, x+1/4, z+1/4; (ii) x, y+1, z+1; (iii) x+1/2, y+1, z+1/2.
 

Acknowledgements

The authors thank the CLRC for funding this work through a beamtime grant (No. RB14118) and Dr Ron Smith, instrument scientist, for his invaluable contribution to the data collection.

References

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