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The ReO3-type structure NbO2F, niobium dioxyfluoride, has been studied at high pressures using diamond anvil cells and synchrotron X-ray radiation. High-pressure powder diffraction measurements have been performed up to 40.1 GPa. A phase transition from the cubic (Pm3m) ambient pressure structure to a rhombohedral (R3c) structure at 0.47 GPa has been observed. Rietveld refinements at 1.38, 1.96, 3.20, 6.23, 9.00 and 10.5 GPa showed that the transition involves an a-a-a- tilting of the cation-anion coordination octahedra and a change of the anion-anion arrangement to approach hexagonal close packing. Compression and distortion of the Nb(O/F)6 octahedra is also revealed by the Rietveld refinements. At 17-18 GPa, the diffraction pattern disappears and the structure becomes X-ray amorphous.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768199015311/ad0088sup1.cif
Contains datablocks global, ambient, 1.38, 1.96, 3.20, 6.23, 9.00, 10.5

Computing details top

(ambient) top
Crystal data top
FNbO2a = 5.52 Å
Mr = 143.9c = 13.52 Å
Trigonal, R3cV = 356.46 Å3
Hall symbol: -R 3 2"cZ = 6
Data collection top
h = l =
k =
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Nb0000.079 (11)
O0.500.250.016 (3)
F0.500.250.016 (3)
Geometric parameters (Å, º) top
Nb—O1.951Nb—Nb3.902
Nb—F1.951O—F2.759
O—Nb—F90Nb—O—Nb180
O—Nb—F180
(1.38) top
Crystal data top
FNbO2a = 5.3067 (4) Å
Mr = 143.9c = 13.5495 (8) Å
Trigonal, R3cV = 330.45 (3) Å3
Hall symbol: -R 3 2"cZ = 6
Data collection top
h = l =
k =
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Nb0000.079 (11)
O0.4232 (17)00.250.016 (3)
F0.4232 (17)00.250.016 (3)
Geometric parameters (Å, º) top
Nb—O1.946 (1)O—F2.746 (5)
Nb—F1.946 (1)O—F2.759 (4)
Nb—Nb3.8061 (4)O—F3.290 (4)
O—F2.745 (6)
O—Nb—F89.7O—Nb—F180.0 (5)
O—Nb—F90.3Nb—O—Nb155.8 (3)
(1.96) top
Crystal data top
FNbO2a = 5.2357 (3) Å
Mr = 143.9c = 13.5542 (12) Å
Trigonal, R3cV = 321.78 (2) Å3
Hall symbol: -R 3 2"cZ = 6
Data collection top
h = l =
k =
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Nb0000.0266 (8)
O0.4112 (9)00.250.0031 (18)
F0.4112 (9)00.250.0031 (18)
Geometric parameters (Å, º) top
Nb—O1.943 (1)O—F2.757 (3)
Nb—F1.944 (4)O—F2.758 (4)
Nb—Nb3.7737 (3)O—F3.119 (4)
O—F2.739 (6)
O—Nb—F89.6 (2)O—Nb—F180.0 (5)
O—Nb—F90.4 (2)Nb—O—Nb152.3 (3)
(3.20) top
Crystal data top
FNbO2a = 5.1232 (4) Å
Mr = 143.9c = 13.6017 (17) Å
Trigonal, R3cV = 309.18 (2) Å3
Hall symbol: -R 3 2"cZ = 6
Data collection top
h = l =
k =
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Nb0000.0208 (5)
O0.3912 (8)00.250.0074 (18)
F0.3912 (8)00.250.0074 (18)
Geometric parameters (Å, º) top
Nb—O1.945 (2)O—F2.738 (4)
Nb—F1.945 (5)O—F2.763 (3)
Nb—Nb3.7267O—F2.764 (4)
O—F2.737 (5)
O—Nb—F89.5 (1)O—Nb—F180.0 (7)
O—Nb—F90.5 (1)Nb—O—Nb146.7 (2)
(6.23) top
Crystal data top
FNbO2a = 4.9462 (4) Å
Mr = 143.9c = 13.6689 (18) Å
Trigonal, R3cV = 289.60 (2) Å3
Hall symbol: -R 3 2"cZ = 6
Data collection top
h = l =
k =
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Nb0000.0359 (6)
O0.3748 (6)00.250.0143 (12)
F0.3748 (6)00.250.0143 (12)
Geometric parameters (Å, º) top
Nb—O1.929 (1)O—F2.759 (2)
Nb—F1.929 (2)O—F2.958 (2)
Nb—Nb3.6531 (3)O—F3.211 (2)
O—F2.696 (6)
O—Nb—F88.7 (1)O—Nb—F180 (1)
O—Nb—F91.3 (1)Nb—O—Nb142.5 (2)
(9.00) top
Crystal data top
FNbO2a = 4.8552 (3) Å
Mr = 143.9c = 13.7000 (14) Å
Trigonal, R3cV = 279.68 (2) Å3
Hall symbol: -R 3 2"cZ = 6
Data collection top
h = l =
k =
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Nb0000.0315 (7)
O0.3674 (6)00.250.0127 (13)
F0.3674 (6)00.250.0127 (13)
Geometric parameters (Å, º) top
Nb—O1.919 (1)O—F2.672 (3)
Nb—F1.991 (2)O—F2.755 (2)
Nb—Nb3.6154 (4)O—F2.756 (2)
O—F2.671 (4)O—F2.912 (2)
O—Nb—F88.2 (1)O—Nb—F180.0 (2)
O—Nb—F91.8 (1)Nb—O—Nb140.8 (2)
(10.5) top
Crystal data top
FNbO2a = 4.8232 (3) Å
Mr = 143.9c = 13.7125 (18) Å
Trigonal, R3cV = 276.26 (2) Å3
Hall symbol: -R 3 2"cZ = 6
Data collection top
h = l =
k =
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Nb0000.0302 (8)
O0.3675 (7)00.250.0130 (15)
F0.3675 (7)00.250.0130 (15)
Geometric parameters (Å, º) top
Nb—O1.911 (1)O—F2.654 (4)
Nb—F1.911 (3)O—F2.751 (2)
Nb—Nb3.6024 (5)O—F2.752 (3)
O—F2.653 (4)O—F2.906 (2)
O—Nb—F87.9 (1)O—Nb—F180.0 (1)
O—Nb—F92.1 (1)Nb—O—Nb140.9 (2)
 

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