KCaNb2O6F from a combined synchrotron X-ray and neutron powder diffraction study

Yoo, C.-Y.; Kim, S.-J.

doi:10.1107/S1600536807060436

KCaNb₂O₆F from a combined synchrotron X-ray and neutron powder diffraction study

Potassium calcium diniobium hexaoxide fluoride, KCaNb₂O₆F, crystallizes in the cubic pyrochlore-type structure. In the crystal structure, NbO₆ octahedra are linked together by common corners to form a three-dimensional [Nb₂O₆]^2- network. (K,Ca) and F atoms, which are located in the voids of the [Nb₂O₆]^2- network, form zigzag [(K,Ca)F]²⁺ chains. The K and Ca atoms are distributed statistically over the same crystallographic position (site-occupancy factor = 0.5), having an eightfold coordination by six O atoms from the NbO₆ octahedra and by two F atoms. All atoms lie on special positions, viz. Nb has $\overline{3}$ m, the (K,Ca) site has $\overline{3}$ m, O has 2mm and F has $\overline{4}$ 3m site symmetry.

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Supporting information

	Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536807060436/wm2150sup1.cif Contains datablocks global, I
	Rietveld powder data file (CIF format) https://doi.org/10.1107/S1600536807060436/wm2150Isup2.rtv Contains datablock I

checkCIF report

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

Comment top

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, O^2- = 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.

Related literature top

For a general description of structures and physical properties of pyrochlore-type compounds, see Subramanian et al. (1983). The 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 (von Gaertner, 1930) and LiCaNb₂O₆F (Le Berre et al., 2007). The structural variation with composition in these oxyfluoride homologues has been discussed in the literature (Kim et al., 2002). For rare earth pyrochlores of composition RE₂Sn₂O₇ (RE = La to Lu), see Kennedy et al. (1997). Bond valence parameters were taken from Brese & O'Keeffe (1991), and measured reflections of the title compound were indexed with DICVOL (Boultif & Louër, 2004).

Experimental top

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.

Computing details top

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).

Figures top

	Fig. 1. The local structure around the (K, Ca) site (a), and a schematic view projected along [101] (b). Octahedra represent NbO₆, large and small ellipsoids represent F and (K, Ca) atoms, respectively.
	Fig. 2. Rietveld refinement plots of KCaNb₂O₆F based on synchrotron X-ray (a) and neutron (b) powder diffraction data.

Potassium calcium diniobium hexaoxide fluoride top

Crystal data top

KCaNb₂O₆F	Neutron radiation, λ = 1.83480 Å
M_r = 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
D_x = 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	T_min = ?, T_max = ?
Specimen mounting: vanadium can	2θ_min = −0.5°, 2θ_max = 160°, 2θ_step = 0.05°
Data collection mode: transmission

Refinement top

Refinement on I_net	Excluded region(s): 2θ < 15°, 2θ > 140°
R_p = 4.08	Profile function: pseudo-Voigt
R_wp = 5.64	25 parameters
R_exp = 3.58	0 restraints
R_Bragg = 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
M_r = 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	T_min = ?, T_max = ?
Data collection mode: transmission	2θ_min = −0.5°, 2θ_max = 160°, 2θ_step = 0.05°
Scan method: step

Refinement top

R_p = 4.08	χ² = 2.465
R_wp = 5.64	3200 data points
R_exp = 3.58	25 parameters
R_Bragg = 2.53	0 restraints

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

	x	y	z	U_iso*/U_eq	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)—O1^x	2.7014 (5)
(K,Ca)—F1ⁱⁱ	2.2850 (1)	(K,Ca)—O1^xi	2.7014 (5)
(K,Ca)—F1ⁱⁱⁱ	2.2850 (1)	Nb1—O1^xii	1.9873 (3)
(K,Ca)—F1^iv	2.2850 (1)	Nb1—O1^xiii	1.9873 (3)
(K,Ca)—F1^v	2.2850 (1)	Nb1—O1^xiv	1.9873 (3)
(K,Ca)—F1	2.2850 (1)	Nb1—O1^xi	1.9873 (3)
(K,Ca)—F1^vi	2.2850 (1)	Nb1—O1^xv	1.9873 (3)
(K,Ca)—F1^vii	2.2850 (1)	Nb1—O1^xvi	1.9873 (3)
(K,Ca)—O1^viii	2.7014 (5)	Nb1—(K,Ca)^xvii	3.7313 (4)
(K,Ca)—O1^ix	2.7014 (5)

F1ⁱ—(K,Ca)—F1ⁱⁱ	180.000 (12)	F1ⁱⁱⁱ—(K,Ca)—O1^x	81.59 (1)
F1ⁱ—(K,Ca)—F1ⁱⁱⁱ	9.6 (3)	F1^iv—(K,Ca)—O1^x	98.42 (1)
F1ⁱⁱ—(K,Ca)—F1ⁱⁱⁱ	180.00	F1^v—(K,Ca)—O1^x	81.59 (1)
F1ⁱ—(K,Ca)—F1^iv	180.00	F1—(K,Ca)—O1^x	98.42 (1)
F1ⁱⁱ—(K,Ca)—F1^iv	9.6 (3)	F1^vi—(K,Ca)—O1^x	81.6 (2)
F1ⁱⁱⁱ—(K,Ca)—F1^iv	180 (4)	F1^vii—(K,Ca)—O1^x	98.42 (1)
F1ⁱ—(K,Ca)—F1^v	9.6 (3)	O1^viii—(K,Ca)—O1^x	62.11 (1)
F1ⁱⁱ—(K,Ca)—F1^v	180.00	O1^ix—(K,Ca)—O1^x	117.89 (1)
F1ⁱⁱⁱ—(K,Ca)—F1^v	9.6 (3)	F1ⁱ—(K,Ca)—O1^xi	98.42 (1)
F1^iv—(K,Ca)—F1^v	180.00	F1ⁱⁱ—(K,Ca)—O1^xi	81.59 (1)
F1ⁱ—(K,Ca)—F1	180.00	F1ⁱⁱⁱ—(K,Ca)—O1^xi	98.42 (1)
F1ⁱⁱ—(K,Ca)—F1	9.6 (3)	F1^iv—(K,Ca)—O1^xi	81.59 (1)
F1ⁱⁱⁱ—(K,Ca)—F1	180.00	F1^v—(K,Ca)—O1^xi	98.42 (1)
F1^iv—(K,Ca)—F1	9.6 (3)	F1—(K,Ca)—O1^xi	81.59 (1)
F1^v—(K,Ca)—F1	180.000 (8)	F1^vi—(K,Ca)—O1^xi	98.42 (1)
F1ⁱ—(K,Ca)—F1^vi	5.5 (3)	F1^vii—(K,Ca)—O1^xi	81.6 (2)
F1ⁱⁱ—(K,Ca)—F1^vi	180.00	O1^viii—(K,Ca)—O1^xi	117.89 (1)
F1ⁱⁱⁱ—(K,Ca)—F1^vi	5.5 (3)	O1^ix—(K,Ca)—O1^xi	62.11 (1)
F1^iv—(K,Ca)—F1^vi	180.00	O1^x—(K,Ca)—O1^xi	180.000 (13)
F1^v—(K,Ca)—F1^vi	5.5 (3)	O1^xii—Nb1—O1^xiii	180.000 (12)
F1—(K,Ca)—F1^vi	180.00	O1^xii—Nb1—O1^xiv	89.04 (2)
F1ⁱ—(K,Ca)—F1^vii	180.00	O1^xiii—Nb1—O1^xiv	90.96 (2)
F1ⁱⁱ—(K,Ca)—F1^vii	5.5 (3)	O1^xii—Nb1—O1^xi	90.96 (2)
F1ⁱⁱⁱ—(K,Ca)—F1^vii	180.00	O1^xiii—Nb1—O1^xi	89.04 (2)
F1^iv—(K,Ca)—F1^vii	5.5 (3)	O1^xiv—Nb1—O1^xi	180.000 (5)
F1^v—(K,Ca)—F1^vii	180.00	O1^xii—Nb1—O1^xv	90.96 (2)
F1—(K,Ca)—F1^vii	5.5 (3)	O1^xiii—Nb1—O1^xv	89.04 (2)
F1^vi—(K,Ca)—F1^vii	180.000 (8)	O1^xiv—Nb1—O1^xv	89.04 (2)
F1ⁱ—(K,Ca)—O1^viii	98.42 (1)	O1^xi—Nb1—O1^xv	90.96 (2)
F1ⁱⁱ—(K,Ca)—O1^viii	81.59 (1)	O1^xii—Nb1—O1^xvi	89.04 (2)
F1ⁱⁱⁱ—(K,Ca)—O1^viii	98.42 (1)	O1^xiii—Nb1—O1^xvi	90.96 (2)
F1^iv—(K,Ca)—O1^viii	81.59 (1)	O1^xiv—Nb1—O1^xvi	90.96 (2)
F1^v—(K,Ca)—O1^viii	98.42 (1)	O1^xi—Nb1—O1^xvi	89.04 (2)
F1—(K,Ca)—O1^viii	81.59 (1)	O1^xv—Nb1—O1^xvi	180.00 (2)
F1^vi—(K,Ca)—O1^viii	98.42 (1)	Nb1ⁱⁱ—O1—Nb1^xviii	139.69 (4)
F1^vii—(K,Ca)—O1^viii	81.6 (2)	Nb1ⁱⁱ—O1—(K,Ca)ⁱⁱ	104.44 (1)
F1ⁱ—(K,Ca)—O1^ix	81.59 (1)	Nb1^xviii—O1—(K,Ca)ⁱⁱ	104.44 (1)
F1ⁱⁱ—(K,Ca)—O1^ix	98.42 (1)	Nb1ⁱⁱ—O1—(K,Ca)^xviii	104.44 (1)
F1ⁱⁱⁱ—(K,Ca)—O1^ix	81.59 (1)	Nb1^xviii—O1—(K,Ca)^xviii	104.44 (1)
F1^iv—(K,Ca)—O1^ix	98.42 (1)	(K,Ca)ⁱⁱ—O1—(K,Ca)^xviii	87.36 (2)
F1^v—(K,Ca)—O1^ix	81.59 (1)	(K,Ca)—F1—(K,Ca)^iv	109.47
F1—(K,Ca)—O1^ix	98.42 (1)	(K,Ca)—F1—(K,Ca)ⁱⁱ	109.47
F1^vi—(K,Ca)—O1^ix	81.6 (2)	(K,Ca)^iv—F1—(K,Ca)ⁱⁱ	109.47
F1^vii—(K,Ca)—O1^ix	98.42 (1)	(K,Ca)—F1—(K,Ca)^vii	109.47
O1^viii—(K,Ca)—O1^ix	180.000 (1)	(K,Ca)^iv—F1—(K,Ca)^vii	109.47
F1ⁱ—(K,Ca)—O1^x	81.59 (1)	(K,Ca)ⁱⁱ—F1—(K,Ca)^vii	109.47
F1ⁱⁱ—(K,Ca)—O1^x	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
M_r	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 (°)	2θ_min = −0.5 2θ_max = 160 2θ_step = 0.05

Refinement
R factors and goodness of fit	R_p = 4.08, R_wp = 5.64, R_exp = 3.58, R_Bragg = 2.53, χ² = 2.465
No. of data points	3200
No. of parameters	25

Computer programs: HANARO HRPD beamline software, FULLPROF (Rodríguez-Carvajal, 2001), SHELXS97 (Sheldrick, 1997), DIAMOND (Bergerhoff, 1996).

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.

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