Key indicators
- Powder neutron study
- T = 298 K
- Mean (Nb-O) = 0.000 Å
- Disorder in main residue
- R factor = 0.000
- wR factor = 0.000
- Data-to-parameter ratio = 2.0
checkCIF/PLATON results
No syntax errors found
Alert level C
PLAT301_ALERT_3_C Main Residue Disorder ......................... 7.00 Perc.
PLAT711_ALERT_1_C BOND Unknown or Inconsistent Label .......... K,CA
(K,CA) F1
PLAT711_ALERT_1_C BOND Unknown or Inconsistent Label .......... K,CA
(K,CA) F1
PLAT711_ALERT_1_C BOND Unknown or Inconsistent Label .......... K,CA
(K,CA) F1
PLAT711_ALERT_1_C BOND Unknown or Inconsistent Label .......... K,CA
(K,CA) F1
PLAT711_ALERT_1_C BOND Unknown or Inconsistent Label .......... K,CA
(K,CA) F1
PLAT711_ALERT_1_C BOND Unknown or Inconsistent Label .......... K,CA
(K,CA) F1
PLAT711_ALERT_1_C BOND Unknown or Inconsistent Label .......... K,CA
(K,CA) F1
PLAT711_ALERT_1_C BOND Unknown or Inconsistent Label .......... K,CA
(K,CA) F1
PLAT711_ALERT_1_C BOND Unknown or Inconsistent Label .......... K,CA
(K,CA) O1
PLAT711_ALERT_1_C BOND Unknown or Inconsistent Label .......... K,CA
(K,CA) O1
PLAT711_ALERT_1_C BOND Unknown or Inconsistent Label .......... K,CA
(K,CA) O1
PLAT711_ALERT_1_C BOND Unknown or Inconsistent Label .......... K,CA
(K,CA) O1
PLAT711_ALERT_1_C BOND Unknown or Inconsistent Label .......... NB1
NB1 O1
PLAT711_ALERT_1_C BOND Unknown or Inconsistent Label .......... NB1
NB1 O1
PLAT711_ALERT_1_C BOND Unknown or Inconsistent Label .......... NB1
NB1 O1
PLAT711_ALERT_1_C BOND Unknown or Inconsistent Label .......... NB1
NB1 O1
PLAT711_ALERT_1_C BOND Unknown or Inconsistent Label .......... NB1
NB1 O1
PLAT711_ALERT_1_C BOND Unknown or Inconsistent Label .......... NB1
NB1 O1
PLAT711_ALERT_1_C BOND Unknown or Inconsistent Label .......... NB1
NB1 (K,CA)
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) F1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... O1
O1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... O1
O1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... O1
O1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... F1
F1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... O1
O1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... O1
O1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... O1
O1 (K,CA) O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... O1
O1 NB1 O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... O1
O1 NB1 O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... O1
O1 NB1 O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... O1
O1 NB1 O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... O1
O1 NB1 O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... O1
O1 NB1 O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... O1
O1 NB1 O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... O1
O1 NB1 O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... O1
O1 NB1 O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... O1
O1 NB1 O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... O1
O1 NB1 O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... O1
O1 NB1 O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... O1
O1 NB1 O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... O1
O1 NB1 O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... O1
O1 NB1 O1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... NB1
NB1 O1 NB1
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... NB1
NB1 O1 (K,CA)
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... NB1
NB1 O1 (K,CA)
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... NB1
NB1 O1 (K,CA)
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... NB1
NB1 O1 (K,CA)
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... K,CA
(K,CA) O1 (K,CA)
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... K,CA
(K,CA) F1 (K,CA)
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... K,CA
(K,CA) F1 (K,CA)
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... K,CA
(K,CA) F1 (K,CA)
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... K,CA
(K,CA) F1 (K,CA)
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... K,CA
(K,CA) F1 (K,CA)
PLAT712_ALERT_1_C ANGLE Unknown or Inconsistent Label .......... K,CA
(K,CA) F1 (K,CA)
0 ALERT level A = In general: serious problem
0 ALERT level B = Potentially serious problem
113 ALERT level C = Check and explain
0 ALERT level G = General alerts; check
112 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
0 ALERT type 2 Indicator that the structure model may be wrong or deficient
1 ALERT type 3 Indicator that the structure quality may be low
0 ALERT type 4 Improvement, methodology, query or suggestion
0 ALERT type 5 Informative message, check
KCaNb2O6F was prepared using a solid state reaction between KF and
CaNb2O6. CaNb2O6 was prepared by firing a stoichiometric mixture of
CaCO3 and Nb2O5 at 1373 K for 2 d with intermediate grinding. The
resulting CaNb2O6 was then thoroughly mixed with KF and pressed into
pellets in a glovebox under an anhydrous Ar atmosphere. The pellets were
placed inside a sealed gold tube and heated at 1023 K for 12 h, before cooled
to room temperature at a rate of 2 K min-1. The composition of the product
was confirmed with energy-dispersive X-ray analysis (Jeol JSM-5600 scanning
electron microscope fitted with a Be window detector, Oxford Instruments). The
synchrotron X-ray powder diffraction (SXPD) measurement was performed on
beamline 8 C2-HRPD at Pohang Accelerator Laboratory, Pohang, Korea. The
incident X-rays were vertically collimated by a mirror, and monochromated to
the wavelength of 1.5422 Å by a double-crystal Si(111) monochromator. A
dataset was collected in the range of 10°≤2θ≤130° with a step size of
0.01° (2θ angle). The powder neutron diffraction (PND) data were collected
on the high-resolution powder diffractometer with a 32 He-3 multi-detector
system and a Ge(331) monochromator, installed at the Korea Atomic Energy
Research Institute, Daejeon.
Measured reflections were indexed with DICVOL (Boultif & Louër, 2004) and the
cubic symmetry was confirmed from both SXRD and NPD data. Additional peaks due
to symmetry lowering or impurity phase were not detected. The figures of merit
were M(20) = 49.7, F(20) = 24.0 (0.0083, 100) for NPD and M(20)
= 55.1, F(20) = 25.5 (0.0050, 158) for SXRD measurements. Systematic absences
suggested two possible cubic space groups, viz. centrosymmetric
Fd3m (No. 227) and non-centrosymmetric Fd3 (No. 203).
Both space groups turned out later to give basically the same structure
solution. Thus, the higher symmetric Fd3m was chosen. The
positions of the (K/Ca) and Nb atoms were determined employing direct methods
using the SXRD data, for which a total of 500 'Fobs' amplitude
factors were converted into structure factors and used as an input for
SHELXS97 (Sheldrick, 1997). The positions of anions were then
determined by difference Fourier analyses of both SXRD and PND data. After
this step, the anions were removed from the refinement and the residual
density was calculated. From the difference Fourier maps it was suggested that
all atomic positions are identical with those of the classical pyrochlore
structure: 16d for (K, Ca), 16c for Nb, 48f for O and
8b for the F atom. The anion positions were confirmed from crystal
chemical considerations and from BVS calculations (Brese & O'Keeffe, 1991).
Structure refinements were carried out by the Rietveld method using Fullprof
(Rodríguez-Carvajal, 2001) with pseudo-Voigt peak shapes and refined
backgrounds. Refinement of atomic positions and isotropic displacement
parameters gave the goodness of fit, S = 2.38. The refinements of the
site occupation factors (SOFs) led to 0.502 (1), 0.502 (1) and 1.03 (2) for K, Ca
and F atoms, respectively, which were in good agreement with the nominal
composition. In the final step, the SOFs were fixed to the ideal values and
the anisotropic thermal displacement factors were refined for all atoms, with
constraints for the K and Ca atoms. The structure was refined with origin
choice 2 of space group Fd3m. The refinement plots for SXRD
and NPD data are shown Fig. 2.
Data collection: HANARO HRPD beamline software; cell refinement: FULLPROF (Rodríguez-Carvajal, 2001); data reduction: FULLPROF (Rodríguez-Carvajal, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: FULLPROF (Rodríguez-Carvajal, 2001); molecular graphics: DIAMOND (Bergerhoff, 1996); software used to prepare material for publication: FULLPROF (Rodríguez-Carvajal, 2001).
Potassium calcium diniobium hexaoxide fluoride
top
Crystal data top
KCaNb2O6F | Neutron radiation, λ = 1.83480 Å |
Mr = 380 | µ = 0.09 mm−1 |
Cubic, Fd3m | T = 298 K |
Hall symbol: -F 4vw 2vw 3 | Particle morphology: particle |
a = 10.55376 (12) Å | white |
V = 1175.50 (2) Å3 | cylinder, 10 × 10 mm |
Z = 8 | Specimen preparation: Prepared at 1023 K and 101 kPa |
Dx = 4.294 Mg m−3 | |
Data collection top
HANARO high-resolution powder diffractometer | Scan method: step |
Radiation source: neutron | Absorption correction: for a cylinder mounted on the ϕ axis (Rodríguez-Carvajal, 1990) |
Ge(331) monochromator | Tmin = ?, Tmax = ? |
Specimen mounting: vanadium can | 2θmin = −0.5°, 2θmax = 160°, 2θstep = 0.05° |
Data collection mode: transmission | |
Refinement top
Refinement on Inet | Excluded region(s): 2θ < 15°, 2θ > 140° |
Rp = 4.08 | Profile function: pseudo-Voigt |
Rwp = 5.64 | 25 parameters |
Rexp = 3.58 | 0 restraints |
RBragg = 2.53 | Weighting scheme based on measured s.u.'s |
χ2 = 2.465 | (Δ/σ)max < 0.001 |
3200 data points | Preferred orientation correction: none |
Crystal data top
KCaNb2O6F | Z = 8 |
Mr = 380 | Neutron radiation, λ = 1.83480 Å |
Cubic, Fd3m | µ = 0.09 mm−1 |
a = 10.55376 (12) Å | T = 298 K |
V = 1175.50 (2) Å3 | cylinder, 10 × 10 mm |
Data collection top
HANARO high-resolution powder diffractometer | Absorption correction: for a cylinder mounted on the ϕ axis (Rodríguez-Carvajal, 1990) |
Specimen mounting: vanadium can | Tmin = ?, Tmax = ? |
Data collection mode: transmission | 2θmin = −0.5°, 2θmax = 160°, 2θstep = 0.05° |
Scan method: step | |
Refinement top
Rp = 4.08 | χ2 = 2.465 |
Rwp = 5.64 | 3200 data points |
Rexp = 3.58 | 25 parameters |
RBragg = 2.53 | 0 restraints |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | Occ. (<1) |
K | 0.25000 | 0.25000 | 0.50000 | 0.0180 (7) | 0.50000 |
Ca | 0.25000 | 0.25000 | 0.50000 | 0.0180 (7) | 0.50000 |
Nb | 0.50000 | 0.00000 | 0.50000 | 0.0124 (3) | |
O | 0.31488 (7) | 0.12500 | 0.12500 | 0.0118 (4) | |
F | 0.37500 | 0.37500 | 0.37500 | 0.0399 (8) | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
K | 0.0180 (7) | 0.0180 (7) | 0.0180 (7) | −0.0013 (5) | −0.0013 (5) | −0.0013 (5) |
Ca | 0.0180 (7) | 0.0180 (7) | 0.0180 (7) | −0.0013 (5) | −0.0013 (5) | −0.0013 (5) |
Nb | 0.0124 (3) | 0.0124 (3) | 0.0124 (3) | −0.0002 (4) | −0.0002 (4) | −0.0002 (4) |
O | 0.0128 (4) | 0.0114 (3) | 0.0114 (3) | 0.00000 | 0.00000 | 0.0046 (4) |
F | 0.0399 (8) | 0.0399 (8) | 0.0399 (8) | 0.00000 | 0.00000 | 0.00000 |
Geometric parameters (Å, º) top
(K,Ca)—F1i | 2.2850 (1) | (K,Ca)—O1x | 2.7014 (5) |
(K,Ca)—F1ii | 2.2850 (1) | (K,Ca)—O1xi | 2.7014 (5) |
(K,Ca)—F1iii | 2.2850 (1) | Nb1—O1xii | 1.9873 (3) |
(K,Ca)—F1iv | 2.2850 (1) | Nb1—O1xiii | 1.9873 (3) |
(K,Ca)—F1v | 2.2850 (1) | Nb1—O1xiv | 1.9873 (3) |
(K,Ca)—F1 | 2.2850 (1) | Nb1—O1xi | 1.9873 (3) |
(K,Ca)—F1vi | 2.2850 (1) | Nb1—O1xv | 1.9873 (3) |
(K,Ca)—F1vii | 2.2850 (1) | Nb1—O1xvi | 1.9873 (3) |
(K,Ca)—O1viii | 2.7014 (5) | Nb1—(K,Ca)xvii | 3.7313 (4) |
(K,Ca)—O1ix | 2.7014 (5) | | |
| | | |
F1i—(K,Ca)—F1ii | 180.000 (12) | F1iii—(K,Ca)—O1x | 81.59 (1) |
F1i—(K,Ca)—F1iii | 9.6 (3) | F1iv—(K,Ca)—O1x | 98.42 (1) |
F1ii—(K,Ca)—F1iii | 180.00 | F1v—(K,Ca)—O1x | 81.59 (1) |
F1i—(K,Ca)—F1iv | 180.00 | F1—(K,Ca)—O1x | 98.42 (1) |
F1ii—(K,Ca)—F1iv | 9.6 (3) | F1vi—(K,Ca)—O1x | 81.6 (2) |
F1iii—(K,Ca)—F1iv | 180 (4) | F1vii—(K,Ca)—O1x | 98.42 (1) |
F1i—(K,Ca)—F1v | 9.6 (3) | O1viii—(K,Ca)—O1x | 62.11 (1) |
F1ii—(K,Ca)—F1v | 180.00 | O1ix—(K,Ca)—O1x | 117.89 (1) |
F1iii—(K,Ca)—F1v | 9.6 (3) | F1i—(K,Ca)—O1xi | 98.42 (1) |
F1iv—(K,Ca)—F1v | 180.00 | F1ii—(K,Ca)—O1xi | 81.59 (1) |
F1i—(K,Ca)—F1 | 180.00 | F1iii—(K,Ca)—O1xi | 98.42 (1) |
F1ii—(K,Ca)—F1 | 9.6 (3) | F1iv—(K,Ca)—O1xi | 81.59 (1) |
F1iii—(K,Ca)—F1 | 180.00 | F1v—(K,Ca)—O1xi | 98.42 (1) |
F1iv—(K,Ca)—F1 | 9.6 (3) | F1—(K,Ca)—O1xi | 81.59 (1) |
F1v—(K,Ca)—F1 | 180.000 (8) | F1vi—(K,Ca)—O1xi | 98.42 (1) |
F1i—(K,Ca)—F1vi | 5.5 (3) | F1vii—(K,Ca)—O1xi | 81.6 (2) |
F1ii—(K,Ca)—F1vi | 180.00 | O1viii—(K,Ca)—O1xi | 117.89 (1) |
F1iii—(K,Ca)—F1vi | 5.5 (3) | O1ix—(K,Ca)—O1xi | 62.11 (1) |
F1iv—(K,Ca)—F1vi | 180.00 | O1x—(K,Ca)—O1xi | 180.000 (13) |
F1v—(K,Ca)—F1vi | 5.5 (3) | O1xii—Nb1—O1xiii | 180.000 (12) |
F1—(K,Ca)—F1vi | 180.00 | O1xii—Nb1—O1xiv | 89.04 (2) |
F1i—(K,Ca)—F1vii | 180.00 | O1xiii—Nb1—O1xiv | 90.96 (2) |
F1ii—(K,Ca)—F1vii | 5.5 (3) | O1xii—Nb1—O1xi | 90.96 (2) |
F1iii—(K,Ca)—F1vii | 180.00 | O1xiii—Nb1—O1xi | 89.04 (2) |
F1iv—(K,Ca)—F1vii | 5.5 (3) | O1xiv—Nb1—O1xi | 180.000 (5) |
F1v—(K,Ca)—F1vii | 180.00 | O1xii—Nb1—O1xv | 90.96 (2) |
F1—(K,Ca)—F1vii | 5.5 (3) | O1xiii—Nb1—O1xv | 89.04 (2) |
F1vi—(K,Ca)—F1vii | 180.000 (8) | O1xiv—Nb1—O1xv | 89.04 (2) |
F1i—(K,Ca)—O1viii | 98.42 (1) | O1xi—Nb1—O1xv | 90.96 (2) |
F1ii—(K,Ca)—O1viii | 81.59 (1) | O1xii—Nb1—O1xvi | 89.04 (2) |
F1iii—(K,Ca)—O1viii | 98.42 (1) | O1xiii—Nb1—O1xvi | 90.96 (2) |
F1iv—(K,Ca)—O1viii | 81.59 (1) | O1xiv—Nb1—O1xvi | 90.96 (2) |
F1v—(K,Ca)—O1viii | 98.42 (1) | O1xi—Nb1—O1xvi | 89.04 (2) |
F1—(K,Ca)—O1viii | 81.59 (1) | O1xv—Nb1—O1xvi | 180.00 (2) |
F1vi—(K,Ca)—O1viii | 98.42 (1) | Nb1ii—O1—Nb1xviii | 139.69 (4) |
F1vii—(K,Ca)—O1viii | 81.6 (2) | Nb1ii—O1—(K,Ca)ii | 104.44 (1) |
F1i—(K,Ca)—O1ix | 81.59 (1) | Nb1xviii—O1—(K,Ca)ii | 104.44 (1) |
F1ii—(K,Ca)—O1ix | 98.42 (1) | Nb1ii—O1—(K,Ca)xviii | 104.44 (1) |
F1iii—(K,Ca)—O1ix | 81.59 (1) | Nb1xviii—O1—(K,Ca)xviii | 104.44 (1) |
F1iv—(K,Ca)—O1ix | 98.42 (1) | (K,Ca)ii—O1—(K,Ca)xviii | 87.36 (2) |
F1v—(K,Ca)—O1ix | 81.59 (1) | (K,Ca)—F1—(K,Ca)iv | 109.47 |
F1—(K,Ca)—O1ix | 98.42 (1) | (K,Ca)—F1—(K,Ca)ii | 109.47 |
F1vi—(K,Ca)—O1ix | 81.6 (2) | (K,Ca)iv—F1—(K,Ca)ii | 109.47 |
F1vii—(K,Ca)—O1ix | 98.42 (1) | (K,Ca)—F1—(K,Ca)vii | 109.47 |
O1viii—(K,Ca)—O1ix | 180.000 (1) | (K,Ca)iv—F1—(K,Ca)vii | 109.47 |
F1i—(K,Ca)—O1x | 81.59 (1) | (K,Ca)ii—F1—(K,Ca)vii | 109.47 |
F1ii—(K,Ca)—O1x | 98.42 (1) | | |
Symmetry codes: (i) x−1/4, −y+1/2, z+1/4; (ii) −x+3/4, y, −z+3/4; (iii) −x+1/2, y−1/4, z+1/4; (iv) x, −y+3/4, −z+3/4; (v) −x+1/2, −y+1/2, −z+1; (vi) x−1/4, y−1/4, −z+1; (vii) −x+3/4, −y+3/4, z; (viii) −y+1/2, −z+1/2, −x+1; (ix) y, z, x; (x) y, −x+3/4, −z+3/4; (xi) −y+1/2, x−1/4, z+1/4; (xii) −y+1/2, z−1/4, x+1/4; (xiii) y+1/2, −z+1/4, −x+3/4; (xiv) y+1/2, −x+1/4, −z+3/4; (xv) x+1/4, y−1/4, −z+1/2; (xvi) −x+3/4, −y+1/4, z+1/2; (xvii) −x+3/4, y−1/2, −z+5/4; (xviii) −x+3/4, −y+1/4, z−1/2. |
Experimental details
Crystal data |
Chemical formula | KCaNb2O6F |
Mr | 380 |
Crystal system, space group | Cubic, Fd3m |
Temperature (K) | 298 |
a (Å) | 10.55376 (12) |
V (Å3) | 1175.50 (2) |
Z | 8 |
Radiation type | Neutron, λ = 1.83480 Å |
µ (mm−1) | 0.09 |
Specimen shape, size (mm) | Cylinder, 10 × 10 |
|
Data collection |
Diffractometer | HANARO high-resolution powder diffractometer |
Specimen mounting | Vanadium can |
Data collection mode | Transmission |
Scan method | Step |
Absorption correction | For a cylinder mounted on the ϕ axis (Rodríguez-Carvajal, 1990) |
2θ values (°) | 2θmin = −0.5 2θmax = 160 2θstep = 0.05 |
|
Refinement |
R factors and goodness of fit | Rp = 4.08, Rwp = 5.64, Rexp = 3.58, RBragg = 2.53, χ2 = 2.465 |
No. of data points | 3200 |
No. of parameters | 25 |
Selected bond lengths (Å) top(K,Ca)—F1 | 2.2850 (1) | Nb1—O1ii | 1.9873 (3) |
(K,Ca)—O1i | 2.7014 (5) | | |
Symmetry codes: (i) y, z, x; (ii) −x+3/4, −y+1/4, z+1/2. |
KCaNb2O6F is isotypic with NaCaNb2O6F (von Gaertner, 1930), typical examples of cubic pyrochlore-type structures. A general description of structures and physical properties of pyrochlore-type compounds was given by Subramanian et al. (1983). Oxyfluoride compounds with general composition A2Nb2O6F (A = alkali metal and alkaline-earth metal) crystallize in different structural types, depending on the size of the A-cation. The layered perovskite-type structure is the most stable structure for large cations as observed in KSrNb2O6F (Yoo et al., 2007) and RbSrNb2O6F (Choy et al., 2001), while the pyrochlore structure is favorable for small A-cations as in NaCaNb2O6F and LiCaNb2O6F (Le Berre et al., 2007). The structural variation on composition in these oxyfluoride homologues has been discussed in the literature (Kim et al. 2002).
In the title compound, the (K, Ca) atoms are located at 16d sites, Nb atoms at 16c, O atoms at 48f and F atoms at 8b sites. (K, Ca) atoms are coordinated to two F atoms and six O atoms, forming a puckered hexagonal bipyramid which is axially compressed with the two F atoms being at considerably shorter distances than the six O atoms. The bond compression inhibits the displacement of the (K, Ca) atoms toward the two closest F atoms, which results in the large anisotropic displacement ellipsoid of the F atom as shown in Fig. 1(a). The Nb atoms are bonded to six O atoms at equal distances forming nearly regular octahedra. By neglecting the K/Ca—O interaction, the structure can be regarded as two interpenetrating networks of Nb2O6 and (K, Ca)2F units, the latter with an anti-cristobalite type arrangement (Fig. 1 b). The bond valence sums (BVS) calculated from the bond distances using the parameters of Brese and O'Keeffe (1991) are (K+, Ca2+) = 1.81, Nb5+ = 4.86, O2- = 1.97 and F- = 1.51. These values imply that the (K, Ca)–F bond is compressed while the Nb—O bond is slightly stretched. Such strong bond compression has been commonly observed in A2B2O7 pyrochlores containing large A-cations. For example, the BVS for O at the 8b site shows a variation from 2.00 for Lu2Sn2O7 to 2.60 for La2Sn2O7 (Kennedy et al., 1997). Taking into consideration that KCaNb2O6F is located near the upper boundary of the stability range for the pyrochlore structures due to the large size of the A-cations, the strong compression of the K/Ca–F bond could be anticipated. The origin of the large variation in BVS for the F ion is, however, still unclear. In this regard, solid state 19F-NMR spectroscopy may be helpful for further studies.