research papers
The crystal structures of three polymorphs of K3GaF6 and the transition temperatures between these phases are reported for the first time. Synchrotron powder diffraction data clearly show that at 300 K α-K3GaF6 crystallizes in space group I41/a with lattice parameters of a = 19.1124 (3) Å, c = 34.4165 (6) Å, and Z = 80. The structure is based on the double perovskite but with two fifths of the GaF6 octahedra rotated by ∼45°. This phase remains stable until ∼460 K, above which it undergoes a transition to I4/m with lattice parameters of a = 13.6088 (4) Å, c = 8.6764 (3) Å, and Z = 10 at 485 K. β-K3GaF6 has a similar structure but with only one fifth of the GaF6 rotated by ∼45°. Above ∼510 K, the cubic Fm3m δ-K3GaF6 structure is stabilized, with a lattice parameter of a = 8.6649 (1) Å at 550 K. The F atoms have highly anisotropic displacement parameters which suggest dynamic octahedral tilting is occurring. This work expands the fairly small group of double perovskite compounds which display non-cooperative patterns of octahedral tilting.
Keywords: double perovskite; non-cooperative octahedral tilting; phase transitions; synchrotron powder diffraction; large unit-cell volume.
Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S2052520620009695/je5027sup1.cif | |
Rietveld powder data file (CIF format) https://doi.org/10.1107/S2052520620009695/je5027K3GaF6_alphasup2.rtv | |
Rietveld powder data file (CIF format) https://doi.org/10.1107/S2052520620009695/je5027K3GaF6_I4_msup3.rtv | |
Rietveld powder data file (CIF format) https://doi.org/10.1107/S2052520620009695/je5027K3GaF6_Fm-3msup4.rtv | |
Portable Document Format (PDF) file https://doi.org/10.1107/S2052520620009695/je5027sup4.pdf |
CCDC references: 2016758; 2016759; 2016760
Computing details top
(K3GaF6_alpha) top
Crystal data top
F120Ga20K60 | c = 34.4165 (6) Å |
Mr = 6020.04 | V = 12573.2 (4) Å3 |
Tetragonal, I41/a | Z = 4 |
a = 19.1124 (3) Å | Dx = 3.180 Mg m−3 |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
x | y | z | Uiso*/Ueq | ||
K1 | 0.00000 | 0.25000 | 0.3651 (11) | 0.0171 (14)* | |
K2 | 0.8898 (12) | 0.4468 (14) | 0.5118 (8) | 0.0171* | |
K3 | 0.1961 (14) | 0.3217 (13) | 0.4966 (7) | 0.0171* | |
K4 | 0.0861 (10) | 0.5600 (11) | 0.3780 (7) | 0.0171* | |
K5 | 0.2035 (13) | 0.3246 (14) | 0.3749 (8) | 0.0171* | |
K6 | 0.00000 | 0.25000 | 0.5040 (10) | 0.0171* | |
K7 | 0.9003 (11) | 0.4539 (11) | 0.3649 (7) | 0.0171* | |
K8 | 0.9280 (10) | 0.0938 (12) | 0.3212 (6) | 0.016 (2)* | |
K9 | 0.8680 (13) | 0.3237 (12) | 0.4340 (8) | 0.0164* | |
K10 | 0.00000 | 0.25000 | 0.62500 | 0.0171* | |
K11 | 0.6912 (14) | 0.8355 (12) | 0.7448 (7) | 0.0171* | |
K12 | 0.1663 (14) | 0.6827 (13) | 0.3051 (7) | 0.0164* | |
K13 | 0.7263 (12) | 0.5110 (15) | 0.3113 (10) | 0.0164* | |
K14 | 0.1023 (14) | 0.0447 (14) | 0.2545 (7) | 0.0171* | |
K15 | 0.00000 | 0.25000 | −0.0063 (10) | 0.0171* | |
K16 | 0.0958 (13) | 0.0480 (12) | 0.1182 (7) | 0.0171* | |
K17 | 0.00000 | 0.25000 | 0.12500 | 0.0171* | |
K18 | 0.0733 (10) | 0.9058 (12) | 0.9359 (9) | 0.0164* | |
Ga19 | 0.0543 (8) | 0.3990 (7) | 0.4367 (4) | 0.0155 (6)* | |
Ga20 | 0.6493 (8) | 0.6983 (7) | 0.8122 (5) | 0.0155* | |
Ga21 | 0.5502 (7) | 0.8987 (7) | 0.1882 (5) | 0.0155* | |
Ga22 | 0.2474 (8) | 0.5008 (7) | 0.0618 (5) | 0.0155* | |
Ga23 | 0.5483 (6) | 0.8979 (7) | 0.6874 (4) | 0.0155* | |
F1 | 0.107 (2) | 0.425 (3) | 0.4788 (12) | 0.0150 (15)* | |
F2 | −0.017 (2) | 0.378 (3) | 0.3967 (12) | 0.0150* | |
F3 | 0.736 (2) | 0.740 (2) | 0.8148 (17) | 0.0150* | |
F4 | 0.555 (2) | 0.649 (2) | 0.8112 (15) | 0.0150* | |
F5 | 0.636 (2) | 0.937 (2) | 0.1814 (15) | 0.0150* | |
F6 | 0.022 (2) | 0.4921 (19) | 0.4381 (17) | 0.0150* | |
F7 | 0.098 (3) | 0.315 (2) | 0.4299 (15) | 0.0150* | |
F8 | 0.606 (3) | 0.784 (2) | 0.8145 (17) | 0.0150* | |
F9 | 0.687 (2) | 0.6064 (19) | 0.8127 (17) | 0.0150* | |
F10 | 0.505 (2) | 0.985 (2) | 0.1863 (19) | 0.0150* | |
F11 | 0.554 (3) | 0.912 (3) | 0.2413 (11) | 0.0150* | |
F12 | −0.019 (2) | 0.371 (3) | 0.4743 (13) | 0.0150* | |
F13 | 0.120 (2) | 0.426 (2) | 0.3959 (12) | 0.0150* | |
F14 | 0.651 (3) | 0.696 (3) | 0.8675 (11) | 0.0150* | |
F15 | 0.660 (3) | 0.692 (3) | 0.7582 (11) | 0.0150* | |
F16 | 0.468 (2) | 0.848 (2) | 0.1861 (15) | 0.0150* | |
F17 | 0.598 (2) | 0.814 (2) | 0.1867 (17) | 0.0150* | |
F18 | 0.549 (3) | 0.889 (3) | 0.1340 (10) | 0.0150* | |
F19 | 0.279 (2) | 0.5946 (19) | 0.0640 (16) | 0.0150* | |
F20 | 0.162 (2) | 0.533 (2) | 0.0623 (16) | 0.0150* | |
F21 | 0.2579 (19) | 0.501 (3) | 0.1156 (10) | 0.0150* | |
F22 | 0.225 (2) | 0.402 (2) | 0.0684 (13) | 0.0150* | |
F23 | 0.337 (2) | 0.467 (2) | 0.0626 (15) | 0.0150* | |
F24 | 0.261 (2) | 0.495 (3) | 0.0092 (10) | 0.0150* | |
F25 | 0.629 (2) | 0.956 (3) | 0.6879 (19) | 0.0150* | |
F26 | 0.496 (2) | 0.982 (2) | 0.6918 (17) | 0.0150* | |
F27 | 0.562 (3) | 0.901 (3) | 0.7461 (10) | 0.0150* | |
F28 | 0.468 (2) | 0.854 (3) | 0.7054 (12) | 0.0150* | |
F29 | 0.600 (2) | 0.812 (2) | 0.6869 (16) | 0.0150* | |
F30 | 0.526 (2) | 0.894 (3) | 0.6360 (11) | 0.0150* |
(K3GaF6_I4_m) top
Crystal data top
F30Ga5K15 | c = 8.6764 (3) Å |
Mr = 1505.01 | V = 1606.9 (1) Å3 |
Tetragonal, I4/m | Z = 2 |
a = 13.6088 (4) Å | Dx = 3.111 Mg m−3 |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
x | y | z | Uiso*/Ueq | ||
K1 | 0.8033 (4) | 0.0972 (4) | 0.2500 | 0.0711 (6)* | |
K2 | 0.5000 | 0.0000 | 0.7500 | 0.0711* | |
K3 | 0.0000 | 0.0000 | 0.5000 | 0.0757 (11)* | |
K4 | 0.9114 (7) | 0.2745 (7) | 0.0000 | 0.0757* | |
Ga1 | 0.0000 | 0.0000 | 0.0000 | 0.0203 (4)* | |
Ga2 | 0.6996 (3) | 0.9003 (2) | 0.5000 | 0.0203* | |
F1 | 0.0545 (18) | 0.1291 (12) | 0.0000 | 0.0468 (9)* | |
F2 | 0.8443 (19) | 0.4690 (9) | 0.0000 | 0.0468* | |
F3 | 0.1767 (9) | 0.0473 (16) | 0.5000 | 0.0468* | |
F4 | 0.3144 (8) | 0.0651 (7) | 0.7089 (6) | 0.0468* | |
F5 | 0.7594 (19) | 0.7740 (9) | 0.5000 | 0.0468* | |
F6 | 0.8566 (16) | 0.4264 (9) | 0.5000 | 0.0468* | |
F7 | 0.0000 | 0.0000 | 0.2089 (6) | 0.0468* |
(K3GaF6_Fm-3m) top
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
x | y | z | Uiso*/Ueq | ||
Ka | 0.25000 | 0.25000 | 0.25000 | 0.0737 (7)* | |
Kb | 0.00000 | 0.00000 | 0.00000 | 0.0972 (12)* | |
Ga | 0.50000 | 0.50000 | 0.50000 | 0.0209 (5)* | |
F | 0.2902 (2) | 0.00000 | 0.00000 | 0.121 |
Atomic displacement parameters (Å2) top
U11 | U22 | U33 | U12 | U13 | U23 | |
F | 0.0285 (18) | 0.1670 (18) | 0.1670 (18) | 0.0000 | 0.0000 | 0.0000 |