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In this work we synthesized BaTaO
2N and SrTaO
2N using a two-step high-temperature solid-state reaction method and analysed the structural distortions, relative to the ideal cubic perovskite structure, according to group theory. From a complete distortion analysis/refinement using high-resolution neutron diffraction data in the temperature range 8 to 613 K, we identified tetragonal structures for BaTaO
2N [
P4/
mmm (No. 123)] and SrTaO
2N [
I4/
mcm (No. 140)]. In contrast to an anion-disordered cubic perovskite (
No. 221) with Ta at the cell center, both systems show a site preference for oxygen anions in the two opposite corners (along the
c axis) of the Ta–O/N octahedra rather than the four square corners in the
ab plane (
Γ3+ occupancy distortion), which induces a tetragonal elongation of the unit cell with the
c axis being longer than the
a axis. A further Ta–O/N octahedra displacement [
R5−(
a,0,0), rotation about the
c axis] distortion was observed in SrTaO
2N. This distortion mode is accompanied by an increased unit-cell distortion that decreases as the temperature increases. Ultimately a second-order phase transition caused by the loss of the
R5−(
a,0,0) mode was observed at 400–450 K.
Supporting information
| Crystallographic Information File (CIF) https://doi.org/10.1107/S2052520617001123/dq5022sup1.cif Contains datablocks I, II, III, IV, V, VI, VII, VIII |
| Rietveld powder data file (CIF format) https://doi.org/10.1107/S2052520617001123/dq5022Isup2.rtv Contains datablock I |
| Rietveld powder data file (CIF format) https://doi.org/10.1107/S2052520617001123/dq5022IIsup3.rtv Contains datablocks II, pxrd_../data/hrp63851_b2_tof.dat |
| Rietveld powder data file (CIF format) https://doi.org/10.1107/S2052520617001123/dq5022IIIsup4.rtv Contains datablocks III, pxrd_../data/hrp63855_b2_tof.dat |
| Rietveld powder data file (CIF format) https://doi.org/10.1107/S2052520617001123/dq5022IVsup5.rtv Contains datablocks IV, pxrd_../data/hrp63855_b2_tof.dat |
| Rietveld powder data file (CIF format) https://doi.org/10.1107/S2052520617001123/dq5022Vsup6.rtv Contains datablock V |
| Rietveld powder data file (CIF format) https://doi.org/10.1107/S2052520617001123/dq5022VIsup7.rtv Contains datablocks VI, pxrd_../data/hrp63965_b2_tof.dat |
| Rietveld powder data file (CIF format) https://doi.org/10.1107/S2052520617001123/dq5022VIIsup8.rtv Contains datablocks VII, pxrd_../data/hrp63963_b2_tof.dat |
| Rietveld powder data file (CIF format) https://doi.org/10.1107/S2052520617001123/dq5022VIIIsup9.rtv Contains datablocks VIII, pxrd_../data/hrp63963_b2_tof.dat |
Crystal data top
P4/mmm | β = 90° |
a = 4.10502 (6) Å | γ = 90° |
b = 4.10502 (6) Å | V = 69.24 (1) Å3 |
c = 4.10874 (12) Å | T = 9 K |
α = 90° | |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Biso*/Beq | Occ. (<1) |
Ba1 | 0 | 0 | 0 | 0.220 (17) | |
Ta1 | 0.5 | 0.5 | 0.5 | 0.671 (18) | |
O1 | 0 | 0.5 | 0.5 | 0.578 (15) | 0.579 (8) |
O2 | 0.5 | 0.5 | 0 | 0.578 (15) | 0.844 (17) |
N1 | 0 | 0.5 | 0.5 | 0.578 (15) | 0.421 (8) |
N2 | 0.5 | 0.5 | 0 | 0.578 (15) | 0.156 (17) |
Crystal data top
P4/mmm | β = 90° |
a = 4.11061 (6) Å | γ = 90° |
b = 4.11061 (6) Å | V = 69.53 (1) Å3 |
c = 4.11475 (11) Å | T = 300 K |
α = 90° | |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Biso*/Beq | Occ. (<1) |
Ba1 | 0 | 0 | 0 | 0.48 (2) | |
Ta1 | 0.5 | 0.5 | 0.5 | 0.84 (2) | |
O1 | 0 | 0.5 | 0.5 | 0.752 (17) | 0.565 (4) |
O2 | 0.5 | 0.5 | 0 | 0.752 (17) | 0.872 (9) |
N1 | 0 | 0.5 | 0.5 | 0.752 (17) | 0.435 (4) |
N2 | 0.5 | 0.5 | 0 | 0.752 (17) | 0.128 (9) |
Crystal data top
C12/m1 | β = 135.09 (4)° |
a = 8.0579 (12) Å | γ = 90° |
b = 8.0305 (16) Å | V = 259.9 (3) Å3 |
c = 5.690 (4) Å | T = 8 K |
α = 90° | |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Biso*/Beq | Occ. (<1) |
Sr1 | 0.25 | 0 | 0 | 0.50 (3) | |
Ta1 | 0.25 | 0.25 | 0.5 | 0.41 (3) | |
O1 | 0 | 0.27283 (18) | 0 | 1.26 (3) | 0.21 (2) |
O2 | 0 | 0.25 | 0.5 | 1.26 (3) | 0.84 (3) |
O3 | 0.22717 (18) | 0 | 0.4543 (4) | 1.26 (3) | 0.95 (2) |
N1 | 0 | 0.27283 (18) | 0 | 1.26 (3) | 0.79 (2) |
N2 | 0 | 0.25 | 0.5 | 1.26 (3) | 0.16 (3) |
N3 | 0.22717 (18) | 0 | 0.4543 (4) | 1.26 (3) | 0.05 (2) |
Crystal data top
I4/mcm | β = 90° |
a = 5.6837 (8) Å | γ = 90° |
b = 5.6837 (8) Å | V = 260.47 (11) Å3 |
c = 8.0630 (12) Å | T = 8 K |
α = 90° | |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Biso*/Beq | Occ. (<1) |
Sr1 | 0 | 0.5 | 0.25 | 0.54 (3) | |
Ta1 | 0 | 0 | 0 | 0.34 (3) | |
O1 | 0.77213 (14) | 0.27213 (14) | 0 | 1.27 (3) | 0.5 |
O2 | 0 | 0 | 0.25 | 1.27 (3) | |
N1 | 0.77213 (14) | 0.27213 (14) | 0 | 1.27 (3) | 0.5 |
Crystal data top
I4/mcm | β = 90° |
a = 5.6949 (9) Å | γ = 90° |
b = 5.6949 (9) Å | V = 261.66 (13) Å3 |
c = 8.0681 (14) Å | T = 286 K |
α = 90° | |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Biso*/Beq | Occ. (<1) |
Sr1 | 0 | 0.5 | 0.25 | 0.86 (4) | |
Ta1 | 0 | 0 | 0 | 0.55 (4) | |
O1 | 0.76655 (14) | 0.26655 (14) | 0 | 1.50 (4) | 0.5 |
O2 | 0 | 0 | 0.25 | 1.50 (4) | |
N1 | 0.76655 (14) | 0.26655 (14) | 0 | 1.50 (4) | 0.5 |
Crystal data top
I4/mcm | β = 90° |
a = 5.7137 (2) Å | γ = 90° |
b = 5.7137 (2) Å | V = 264.06 (5) Å3 |
c = 8.0885 (10) Å | T = 418 K |
α = 90° | |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Biso*/Beq | Occ. (<1) |
Sr1 | 0 | 0.5 | 0.25 | 0.95 (4) | |
Ta1 | 0 | 0 | 0 | 0.52 (4) | |
O1 | 0.75950 (18) | 0.24050 (18) | 0 | 1.61 (4) | 0.5 |
O2 | 0 | 0 | 0.25 | 1.61 (4) | |
N1 | 0.75950 (18) | 0.24050 (18) | 0 | 1.61 (4) | 0.5 |
Crystal data top
I4/mcm | β = 90° |
a = 5.7224 (3) Å | γ = 90° |
b = 5.7224 (3) Å | V = 265.27 (5) Å3 |
c = 8.1010 (12) Å | T = 603 K |
α = 90° | |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Biso*/Beq | Occ. (<1) |
Sr1 | 0 | 0.5 | 0.25 | 1.24 (5) | |
Ta1 | 0 | 0 | 0 | 0.72 (5) | |
O1 | 0.7551 (4) | 0.2551 (4) | 0 | 1.84 (5) | 0.5 |
O2 | 0 | 0 | 0.25 | 1.84 (5) | |
N1 | 0.7551 (4) | 0.2551 (4) | 0 | 1.84 (5) | 0.5 |
Crystal data top
P4/mmm | β = 90° |
a = 4.04633 (11) Å | γ = 90° |
b = 4.04633 (11) Å | V = 66.32 (1) Å3 |
c = 4.0506 (4) Å | T = 603 K |
α = 90° | |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Biso*/Beq | Occ. (<1) |
Sr1 | 0.00000 | 0.00000 | 0.00000 | 1.26 (5) | |
Ta1 | 0.50000 | 0.50000 | 0.50000 | 0.73 (6) | |
O1 | 0.00000 | 0.50000 | 0.50000 | 1.89 (5) | 0.5 |
O2 | 0.50000 | 0.50000 | 0.00000 | 1.89 (5) | |
N1 | 0.00000 | 0.50000 | 0.50000 | 1.89 (5) | 0.5 |
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