Download citation
Download citation
link to html
The crystal structure of the defect perovskite Ce1/3NbO3, cerium niobium oxide, has been re-examined by neutron powder and electron diffraction. The results of a powder neutron Rietveld refinement indicate that the structure is monoclinic: space group P2/m with Z = 4, a = 5.5267 (3), b = 7.8824 (2), c = 5.5245 (3) Å, β = 90.294 (1)°, V = 240.67 (2) Å3 at 298 K with χ2 = 2.570. Previous reports have described the Ce1/3NbO3 structure in a smaller (V/2) orthorhombic cell based solely upon X-ray powder diffraction data. The presence of weak reflections in the electron diffraction pattern provides conclusive evidence for a monoclinic superstructure of the orthorhombic cell. While these superlattice reflections are barely detectable with X-ray radiation, they are clearly visible in the neutron diffraction experiments. The superlattice reflections are shown to arise from a tilting of the NbO6 octahedra which results in the reduction of symmetry from orthorhombic to monoclinic. It is also found that the Ce3+ and Nb5+ cations are displaced from the centres of their respective polyhedra to accommodate the bond-valence requirements of the crystal structure. It is likely that distortions of this type are present in other Ln1/3NbO3 and Ln1/3TaO3 defect perovskites.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768199012951/br0090sup1.cif
Contains datablocks cenb, cenb_data

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0108768199012951/br0090sup2.rtv
Contains datablocks cenb, cenb_intensity_data

Computing details top

Cell refinement: GSAS; data reduction: GSAS; program(s) used to refine structure: GSAS.

cerium niobium oxide top
Crystal data top
Ce0.33333NbO3V = 240.67 (2) Å3
Mr = 187.61Z = 4
Monoclinic, P2/mDx = 5.173 Mg m3
Hall symbol: -P 2yneutron radiation
a = 5.5267 (3) ŵ = 0.14 (1) mm1
b = 7.8824 (2) ÅT = 298 K
c = 5.5245 (3) Åbrown
β = 90.294 (1)°Specimen preparation: Prepared at 1200 K
Data collection top
SEPD
diffractometer
Absorption correction: part of the refinement model (ΔF)
Debye-Scherrer absorption correction provided in the GSAS powder refinement package (useful for TOF data). Reference: Hewat (1979) A35, 248. NOTE: This value is REFINED (not calculated based upon composition)
Radiation source: spallation
None monochromator2θfixed = 145
Specimen mounting: Vanadium canDistance from source to specimen: 14m mm
Data collection mode: transmissionDistance from specimen to detector: 1.5m mm
Scan method: time of flight
Refinement top
Rp = 0.03560 parameters
Rwp = 0.057(Δ/σ)max = 0.01
Excluded region(s): 0-4, 30-1000(s)Background function: power series
Profile function: Convolution exponentials and a Gaussian
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Ce0.255 (2)0.00.756 (2)0.0120 (6)*.66667
Nb0.2458 (8)0.2613 (2)0.2527 (7)0.01624
O10.271 (1)0.50.286 (1)0.02033
O20.224 (1)0.00.212 (1)0.01881
O30.50.2059 (5)0.50.0154
O40.00.223 (1)0.50.01346
O50.50.242 (1)0.00.02488
O60.00.2626 (5)0.00.02277
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ce0.0120 (6)0.0120 (6)0.0120 (6)0.000.000.00
Nb0.0131 (3)0.0206 (7)0.015 (3)0.007 (1)0.0008 (5)0.003 (1)
O10.023 (4)0.008 (1)0.030 (4)0.000.001 (2)0.00
O20.017 (3)0.009 (1)0.031 (4)0.000.003 (2)0.00
O30.008 (4)0.023 (2)0.015 (4)0.000.008 (2)0.00
O40.012 (4)0.024 (3)0.005 (3)0.000.005 (2)0.00
O50.033 (5)0.028 (4)0.014 (4)0.0013 (2)0.00
O60.033 (5)0.023 (2)0.012 (4)0.0013 (2)0.00
Geometric parameters (Å, º) top
Nb—O1Cei—O2
Nb—O2Ceii—O2
Nb—O3Ceiii—O2
Nb—O4Ce—O3
Nb—O5Ce—O4
Nb—O6Cei—O5
Ce—O2Cei—O6
O2—Ce—O2i172.6 (6)O4—Ce—O5i93.54 (11)
O2—Ce—O2ii90.7 (5)O4—Ce—O5iv176.4 (6)
O2—Ce—O2iii96.6 (3)O4—Ce—O6i60.56 (15)
O2—Ce—O358.26 (19)O4—Ce—O6v118.1 (5)
O2—Ce—O455.9 (3)O5v—Ce—O5iv90.0 (6)
O2—Ce—O5i121.72 (19)O5i—Ce—O6i59.86 (13)
O2—Ce—O6i116.5 (4)O5i—Ce—O6v121.8 (4)
O2—Ce—O2ii81.9 (3)O6i—Ce—O6v93.3 (3)
O2i—Ce—O3126.4 (4)O1—Nb—O2179.1 (5)
O2i—Ce—O4119.4 (2)O1—Nb—O395.7 (3)
O2i—Ce—O5i62.6 (3)O1—Nb—O497.7 (5)
O2i—Ce—O6i59.4 (2)O1—Nb—O595.4 (5)
O2ii—Ce—O2iii172.7 (6)O1—Nb—O696.6 (2)
O2ii—Ce—O3124.8 (4)O2—Nb—O384.26 (16)
O2ii—Ce—O460.6 (3)O2—Nb—O483.2 (4)
O2ii—Ce—O5i117.8 (3)O2—Nb—O583.7 (5)
O2ii—Ce—O6i58.2 (2)O2—Nb—O683.4 (2)
O2iii—Ce—O360.0 (3)O3—Nb—O488.69 (17)
O2iii—Ce—O4124.0 (3)O3—Nb—O588.09 (18)
O2iii—Ce—O5i58.0 (3)O3—Nb—O6167.6 (2)
O2iii—Ce—O6i117.9 (4)O4—Nb—O5166.8 (2)
O3—Ce—O3iv79.1 (3)O4—Nb—O690.98 (19)
O3—Ce—O464.18 (16)O5—Nb—O689.43 (15)
O3—Ce—O4v114.1 (4)Nb—O1—Nbvi166.0 (4)
O3—Ce—O5i63.88 (17)Nb—O2—Nbvii165.7 (3)
O3—Ce—O5iv117.4 (5)Nb—O3—Nbiii154.8 (3)
O3—Ce—O6i93.75 (9)Nb—O4—Nbii162.3 (5)
O3—Ce—O6v172.7 (3)Nb—O5—Nbviii171.2 (6)
O4—Ce—O4v82.9 (6)Nb—O6—Nbix179.4 (3)
Symmetry codes: (i) x, y, z+1; (ii) x, y, z+1; (iii) x+1, y, z+1; (iv) x+1, y, z+1; (v) x, y, z+1; (vi) x, y+1, z; (vii) x, y, z; (viii) x+1, y, z; (ix) x, y, z.
 

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