The commensurate composite σ-structure of β-tantalum

Arakcheeva, A.; Chapuis, G.; Birkedal, H.; Pattison, P.; Grinevitch, V.

doi:10.1107/S0108768103009005

The commensurate composite σ-structure of β-tantalum

A. Arakcheeva, G. Chapuis, H. Birkedal, P. Pattison and V. Grinevitch

The single-crystal investigation of the self-hosting σ-structure of β-tantalum (β-Ta) at 120 K (low-temperature, LT, structure) and at 293 K (RT-I before cooling and RT-II after cooling and rewarming; RT represents room temperature) shows that this structure is indeed a specific two-component composite where the components have the same (or an integer multiple) lattice constants but different space groups. The space groups of both host (H) and guest (G) components cause systematic absences, which result from their intersection. The highest symmetry of a σ-structure can be described as [H: P4₂/mnm; G: P4/mbm (c_G = 0.5c_H); composite: P4₂/mnm]. A complete analysis of possible symmetries is presented in the Appendix. In β-Ta, two components modify their symmetry during the thermal process 293 K (RT-I) ⇒ 120 K (LT) ⇒ 293 K (RT-II): [H: P $\bar 4$ 2₁m; G: P $\bar 4$ 2₁m; composite: P $\bar 4$ 2₁m] ⇒ [H: P $\bar 4$ , G: P4/mbm (c_G = 0.5c_H), composite: P $\bar 4$ ] ⇒ [H: P $\bar 4$ 2₁m, G: P4/mbm (c_G = 0.5c_H), composite: P $\bar 4$ 2₁m]. Thus, the phase transition is reversible with respect to H and irreversible with respect to G.

Keywords: low-temperature σ phase of β-Ta; commensurate composite structure; synchrotron radiation; phase transition; thermal process.

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Supporting information

	Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768103009005/sn0032sup1.cif Contains datablocks global, I, II
	Structure factor file (CIF format) https://doi.org/10.1107/S0108768103009005/sn0032Isup2.hkl Contains datablock I
	Structure factor file (CIF format) https://doi.org/10.1107/S0108768103009005/sn0032IIsup3.hkl Contains datablock II

Computing details top

For both compounds, program(s) used to refine structure: (Jana2000; Petricek and Dusek, 2000); software used to prepare material for publication: (Jana2000; Petricek and Dusek, 2000).

(I) top

Crystal data top

Ta₃₀	Z = 1
M_r = 5428.4	F(000) = 2190
Tetragonal, P4₂1m	D_x = 16.316 (3) Mg m⁻³
a = 10.201 (1) Å	Mo Kα radiation, λ = 0.71073 Å
c = 5.3075 (5) Å	µ = 147.75 mm⁻¹
V = 552.30 (9) Å³

Data collection top

Oxford Instruments CCD diffractometer	R_int = 0.094
Absorption correction: for a sphere (Jana2000; Petricek and Dusek, 2000)	θ_max = 28.1°, θ_min = 3.8°
T_min = 0.028, T_max = 0.050	h = −13→13
5271 measured reflections	k = −11→13
683 independent reflections	l = −6→6
474 reflections with I > 3σ(I)

Refinement top

Refinement on F	Weighting scheme based on measured s.u.'s w = 1/σ²(F)
R[F² > 2σ(F²)] = 0.058	(Δ/σ)_max = 0.001
wR(F²) = 0.040	Δρ_max = 24.22 e Å⁻³
S = 3.93	Δρ_min = −11.35 e Å⁻³
474 reflections	Extinction correction: B-C type 1 Gaussian isotropic (Becker & Coppens, 1974)
24 parameters	Extinction coefficient: 0.000648

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

	x	y	z	U_iso*/U_eq
Ta1	0.5	0	0.247	0.0050 (15)
Ta2	0.7611 (3)	0.0674 (3)	0.2463	0.005
Ta3	0.0343 (3)	0.1286 (3)	0.2415	0.0041 (9)
Ta4	0.1043 (3)	−0.6043 (3)	0.245	0.0046 (10)
Ta5	0.81862 (16)	0.31863 (16)	0	0.0058 (5)
Ta6	0.81862 (16)	0.31863 (16)	0.5	0.0058 (5)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Ta1	0.0069 (19)	0.0069 (19)	0.001 (4)	0.001 (2)	0	0
Ta2	0.005588	0.007159	0.002218	0.000216	−0.00034	−0.003739
Ta3	0.0078 (14)	0.0037 (15)	0.0007 (17)	−0.0015 (10)	0.000 (5)	−0.001 (5)
Ta4	0.0066 (14)	0.0066 (14)	0.001 (2)	−0.0002 (17)	0.001 (6)	−0.001 (6)
Ta5	0.0076 (6)	0.0076 (6)	0.0022 (11)	0.0022 (14)	0	0
Ta6	0.0076 (6)	0.0076 (6)	0.0022 (11)	0.0022 (14)	0	0

Bond lengths (Å) top

Ta1—Ta1ⁱ	5.3075	Ta2—Ta4^viii	5.646 (5)
Ta1—Ta1ⁱⁱ	5.3075	Ta2—Ta5	2.936 (3)
Ta1—Ta2ⁱ	5.9813 (15)	Ta2—Ta5ⁱⁱ	4.786 (2)
Ta1—Ta2	2.751 (3)	Ta2—Ta5ⁱⁱⁱ	4.841 (3)
Ta1—Ta2ⁱⁱ	5.9747 (15)	Ta2—Ta5^xxxviii	5.950 (4)
Ta1—Ta2ⁱⁱⁱ	5.680 (3)	Ta2—Ta5^xl	5.967 (4)
Ta1—Ta2^iv	5.713 (3)	Ta2—Ta5^xiii	2.969 (3)
Ta1—Ta2^v	5.680 (3)	Ta2—Ta5^xiv	4.807 (2)
Ta1—Ta2^vi	5.713 (3)	Ta2—Ta6ⁱ	4.754 (2)
Ta1—Ta2^vii	5.9813 (15)	Ta2—Ta6	2.953 (3)
Ta1—Ta2^viii	2.751 (3)	Ta2—Ta6^iv	4.851 (3)
Ta1—Ta2^ix	5.9747 (15)	Ta2—Ta6^xxxix	5.959 (4)
Ta1—Ta2^x	5.9813 (15)	Ta2—Ta6^xl	5.975 (4)
Ta1—Ta2^xi	2.751 (3)	Ta2—Ta6^xiii	4.774 (2)
Ta1—Ta2^xii	5.9747 (15)	Ta2—Ta6^xiv	2.986 (3)
Ta1—Ta2^xiii	5.680 (3)	Ta3—Ta3ⁱ	5.3075
Ta1—Ta2^xiv	5.713 (3)	Ta3—Ta3ⁱⁱ	5.3075
Ta1—Ta2^xv	5.680 (3)	Ta3—Ta3^xxi	3.203 (3)
Ta1—Ta2^xvi	5.713 (3)	Ta3—Ta3^xxii	3.349 (3)
Ta1—Ta2^xvii	5.9813 (15)	Ta3—Ta3^xliv	5.962 (2)
Ta1—Ta2^xviii	2.751 (3)	Ta3—Ta3^xxv	2.716 (5)
Ta1—Ta2^xix	5.9747 (15)	Ta3—Ta3^xlv	5.962 (2)
Ta1—Ta3	4.929 (3)	Ta3—Ta3^xi	4.863 (5)
Ta1—Ta3^xx	5.606 (3)	Ta3—Ta3^xlvi	3.203 (3)
Ta1—Ta3^xxi	4.604 (3)	Ta3—Ta3^xlvii	3.349 (3)
Ta1—Ta3^xxii	4.674 (3)	Ta3—Ta3^xlviii	5.852 (5)
Ta1—Ta3^xxiii	4.604 (3)	Ta3—Ta4^xlix	5.992 (2)
Ta1—Ta3^xxiv	4.674 (3)	Ta3—Ta4^xxxii	2.816 (5)
Ta1—Ta3^xxv	5.606 (3)	Ta3—Ta4^xxxiii	5.090 (4)
Ta1—Ta3^viii	4.929 (3)	Ta3—Ta4^xxxiv	5.164 (4)
Ta1—Ta3^xxvi	5.606 (3)	Ta3—Ta4^l	5.096 (4)
Ta1—Ta3^xi	4.929 (3)	Ta3—Ta4^li	5.170 (4)
Ta1—Ta3^xxvii	4.604 (3)	Ta3—Ta4^lii	5.532 (5)
Ta1—Ta3^xxviii	4.674 (3)	Ta3—Ta4^xxv	5.054 (5)
Ta1—Ta3^xxix	4.604 (3)	Ta3—Ta5^liii	3.200 (3)
Ta1—Ta3^xxx	4.674 (3)	Ta3—Ta5^liv	4.980 (2)
Ta1—Ta3^xviii	4.929 (3)	Ta3—Ta5ⁱⁱⁱ	3.216 (3)
Ta1—Ta3^xxxi	5.606 (3)	Ta3—Ta5^iv	4.991 (2)
Ta1—Ta4^xxxii	5.708 (3)	Ta3—Ta5^viii	4.971 (4)
Ta1—Ta4^xxxiii	3.0141 (16)	Ta3—Ta5^lv	5.974 (4)
Ta1—Ta4^xxxiv	3.0875 (16)	Ta3—Ta5^lvi	4.960 (4)
Ta1—Ta4^xxxv	3.0141 (16)	Ta3—Ta6^lvii	4.908 (2)
Ta1—Ta4^xxxvi	3.0875 (16)	Ta3—Ta6^liii	3.237 (3)
Ta1—Ta4^xxxvii	5.708 (3)	Ta3—Ta6ⁱⁱⁱ	4.918 (2)
Ta1—Ta5	4.7799 (15)	Ta3—Ta6^iv	3.253 (3)
Ta1—Ta5ⁱⁱⁱ	2.9267 (14)	Ta3—Ta6^viii	4.995 (4)
Ta1—Ta5^iv	4.7768 (9)	Ta3—Ta6^lv	5.994 (4)
Ta1—Ta5^viii	4.7799 (15)	Ta3—Ta6^lviii	4.984 (4)
Ta1—Ta5^xiii	2.9267 (14)	Ta4—Ta4ⁱ	5.3075
Ta1—Ta5^xiv	4.7768 (9)	Ta4—Ta4ⁱⁱ	5.3075
Ta1—Ta6	4.7887 (15)	Ta4—Ta4^lii	3.010 (5)
Ta1—Ta6ⁱⁱⁱ	4.7504 (9)	Ta4—Ta5^lix	3.287 (3)
Ta1—Ta6^iv	2.9409 (14)	Ta4—Ta5^lx	5.017 (2)
Ta1—Ta6^viii	4.7887 (15)	Ta4—Ta5^xxi	3.354 (3)
Ta1—Ta6^xiii	4.7504 (9)	Ta4—Ta5^xxii	5.061 (2)
Ta1—Ta6^xiv	2.9409 (14)	Ta4—Ta5^viii	3.287 (3)
Ta2—Ta2ⁱ	5.3075	Ta4—Ta5^ix	5.017 (2)
Ta2—Ta2ⁱⁱ	5.3075	Ta4—Ta6^lxi	4.975 (2)
Ta2—Ta2^xxxviii	4.434 (4)	Ta4—Ta6^lix	3.308 (3)
Ta2—Ta2^xxxix	4.481 (4)	Ta4—Ta6^xxi	5.019 (2)
Ta2—Ta2^viii	5.502 (5)	Ta4—Ta6^xxii	3.375 (3)
Ta2—Ta2^xl	5.065 (5)	Ta4—Ta6^vii	4.975 (2)
Ta2—Ta2^xi	4.740 (5)	Ta4—Ta6^viii	3.308 (3)
Ta2—Ta2^xiii	4.434 (4)	Ta5—Ta5ⁱ	5.3075
Ta2—Ta2^xiv	4.481 (4)	Ta5—Ta5ⁱⁱ	5.3075
Ta2—Ta2^xv	5.736 (4)	Ta5—Ta5ⁱⁱⁱ	5.289 (2)
Ta2—Ta2^xvi	5.772 (4)	Ta5—Ta5^xxxviii	5.289 (2)
Ta2—Ta2^xli	5.736 (4)	Ta5—Ta5^lxii	5.233 (2)
Ta2—Ta2^xlii	5.772 (4)	Ta5—Ta5^xiii	5.289 (2)
Ta2—Ta2^xvii	5.998 (2)	Ta5—Ta5^xxvii	5.289 (2)
Ta2—Ta2^xviii	2.794 (5)	Ta5—Ta6ⁱ	2.6537
Ta2—Ta2^xix	5.998 (2)	Ta5—Ta6	2.6537
Ta2—Ta3^xx	2.856 (5)	Ta5—Ta6ⁱⁱⁱ	5.918 (2)
Ta2—Ta3^xxxiii	4.673 (4)	Ta5—Ta6^iv	5.918 (2)
Ta2—Ta3^xxxiv	4.746 (4)	Ta5—Ta6^xxxviii	5.918 (2)
Ta2—Ta3^xxiii	4.655 (4)	Ta5—Ta6^xxxix	5.918 (2)
Ta2—Ta3^xxiv	4.728 (4)	Ta5—Ta6^lxiii	5.868 (2)
Ta2—Ta3^viii	2.891 (5)	Ta5—Ta6^lxii	5.868 (2)
Ta2—Ta3^xi	5.684 (5)	Ta5—Ta6^xiii	5.918 (2)
Ta2—Ta3^xxvii	2.8433 (19)	Ta5—Ta6^xiv	5.918 (2)
Ta2—Ta3^xxviii	2.9612 (19)	Ta5—Ta6^xxvii	5.918 (2)
Ta2—Ta3^xxix	5.985 (4)	Ta5—Ta6^xxviii	5.918 (2)
Ta2—Ta3^xviii	5.604 (5)	Ta6—Ta6ⁱ	5.3075
Ta2—Ta3^xxxi	4.951 (5)	Ta6—Ta6ⁱⁱ	5.3075
Ta2—Ta4^xliii	4.845 (5)	Ta6—Ta6^iv	5.289 (2)
Ta2—Ta4^xxxiii	4.875 (4)	Ta6—Ta6^xxxix	5.289 (2)
Ta2—Ta4^xxxiv	4.925 (4)	Ta6—Ta6^lxii	5.233 (2)
Ta2—Ta4^xxxv	3.082 (2)	Ta6—Ta6^xiv	5.289 (2)
Ta2—Ta4^xxxvi	3.160 (2)	Ta6—Ta6^xxviii	5.289 (2)
Ta2—Ta4^xxxvii	4.920 (5)

Symmetry codes: (i) x, y, z−1; (ii) x, y, z+1; (iii) y, −x+1, −z; (iv) y, −x+1, −z+1; (v) x−1/2, −y+1/2, −z; (vi) x−1/2, −y+1/2, −z+1; (vii) −x+1, −y, z−1; (viii) −x+1, −y, z; (ix) −x+1, −y, z+1; (x) −y+1/2, −x+1/2, z−1; (xi) −y+1/2, −x+1/2, z; (xii) −y+1/2, −x+1/2, z+1; (xiii) −y+1, x−1, −z; (xiv) −y+1, x−1, −z+1; (xv) −x+3/2, y−1/2, −z; (xvi) −x+3/2, y−1/2, −z+1; (xvii) y+1/2, x−1/2, z−1; (xviii) y+1/2, x−1/2, z; (xix) y+1/2, x−1/2, z+1; (xx) x+1, y, z; (xxi) y, −x, −z; (xxii) y, −x, −z+1; (xxiii) x+1/2, −y+1/2, −z; (xxiv) x+1/2, −y+1/2, −z+1; (xxv) −x, −y, z; (xxvi) −y+1/2, −x−1/2, z; (xxvii) −y+1, x, −z; (xxviii) −y+1, x, −z+1; (xxix) −x+1/2, y−1/2, −z; (xxx) −x+1/2, y−1/2, −z+1; (xxxi) y+1/2, x+1/2, z; (xxxii) x, y+1, z; (xxxiii) y+1, −x, −z; (xxxiv) y+1, −x, −z+1; (xxxv) x+1/2, −y−1/2, −z; (xxxvi) x+1/2, −y−1/2, −z+1; (xxxvii) −x+1, −y−1, z; (xxxviii) y+1, −x+1, −z; (xxxix) y+1, −x+1, −z+1; (xl) −x+2, −y, z; (xli) −x+3/2, y+1/2, −z; (xlii) −x+3/2, y+1/2, −z+1; (xliii) x+1, y+1, z; (xliv) −x, −y, z−1; (xlv) −x, −y, z+1; (xlvi) −y, x, −z; (xlvii) −y, x, −z+1; (xlviii) y−1/2, x+1/2, z; (xlix) x, y+1, z−1; (l) x−1/2, −y−1/2, −z; (li) x−1/2, −y−1/2, −z+1; (lii) −x, −y−1, z; (liii) x−1, y, z; (liv) x−1, y, z+1; (lv) −x+1, −y+1, z; (lvi) −y, x−1, −z; (lvii) x−1, y, z−1; (lviii) −y, x−1, −z+1; (lix) x−1, y−1, z; (lx) x−1, y−1, z+1; (lxi) x−1, y−1, z−1; (lxii) −x+2, −y+1, z; (lxiii) −x+2, −y+1, z−1.

(II) Metal top

Crystal data top

30.0Ta	D_x = 16.417 (1) Mg m⁻³
M_r = 5428.4	Synchrotron radiation, λ = 0.70013 Å
Tetragonal, P4	Cell parameters from 8379 reflections
a = 10.1815 (5) Å	θ = 3.8–30.5°
c = 5.2950 (1) Å	µ = 148.66 mm⁻¹
V = 548.90 (4) Å³	T = 120 K
Z = 1	Isometric irregular, silver
F(000) = 2190	0.02 × 0.02 × 0.02 × 0.02 (radius) mm

Data collection top

MAR345 diffractometer	1708 independent reflections
Radiation source: bending magnet 1 at ESRF	1530 reflections with I > 3σ(I)
Si(111) double crystal monochromator with bent second crystal for sagital focusing	R_int = 0.082
Detector resolution: 6.667 pixels mm^-1	θ_max = 30.5°, θ_min = 3.8°
φ–scans	h = −14→14
Absorption correction: for a sphere	k = −14→14
T_min = 0.024, T_max = 0.049	l = −7→7
8379 measured reflections

Refinement top

Refinement on F	Weighting scheme based on measured s.u.'s w = 1/(σ²(F) + 0.0001F²)
R[F² > 2σ(F²)] = 0.036	(Δ/σ)_max = 0.001
wR(F²) = 0.050	Δρ_max = 11.04 e Å⁻³
S = 1.74	Δρ_min = −9.89 e Å⁻³
1530 reflections	Extinction correction: B-C type 1 Gaussian isotropic (Becker & Coppens, 1974)
72 parameters	Extinction coefficient: 0.0009 (3)

Special details top

Experimental. The wavelength was calibrated with a standard Si powder pattern. All reflections were involved in a global scaling procedure to correct for beam decay (the measurements were performed on a synchrotron) and inhomogeneities (in beam, sample mount absorption etc.). No assumptions were made about the sample symmetry were made in the scaling procedure, i.e. only repeated measurements were considered equivalent and Friedel's law was not assumed valid.

Cell parameters were determined in a refinement of cell parameters, setting angles and mosaicity after scaling (Otwinowski & Minor, 1997).

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

	x	y	z	U_iso*/U_eq
Ta1	0.5	0	0.2548 (5)	0.0054 (3)
Ta2a	0.75963 (10)	0.06646 (7)	0.2493 (4)	0.0055 (3)
Ta2b	0.43251 (8)	−0.26252 (9)	0.2521 (5)	0.0056 (3)
Ta3a	0.03408 (9)	0.12735 (10)	0.2519 (5)	0.0054 (3)
Ta3b	0.37007 (9)	−0.53527 (9)	0.2488 (5)	0.0057 (3)
Ta4	0.10620 (9)	−0.60509 (9)	0.2513 (4)	0.0056 (3)
Ta5	0.81809 (3)	0.31809 (3)	0	0.00567 (15)
Ta6	0.81809 (3)	0.3181	0.5	0.00567 (15)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Ta1	0.0035 (7)	0.0071 (7)	0.0056 (3)	−0.0009 (2)	0	0
Ta2a	0.0066 (5)	0.0057 (6)	0.0040 (6)	−0.0048 (3)	0.0013 (9)	−0.0010 (9)
Ta2b	0.0054 (5)	0.0039 (5)	0.0075 (6)	0.0040 (3)	0.0012 (9)	0.0006 (8)
Ta3a	0.0064 (4)	0.0062 (5)	0.0036 (5)	−0.0008 (3)	−0.0010 (8)	−0.0010 (9)
Ta3b	0.0035 (5)	0.0052 (4)	0.0083 (7)	0.0006 (3)	−0.0036 (8)	0.0006 (9)
Ta4	0.0068 (5)	0.0041 (5)	0.0059 (3)	−0.00047 (16)	−0.0002 (10)	0.0009 (10)
Ta5	0.0056 (3)	0.0062 (3)	0.0052 (3)	0.00029 (9)	0	0
Ta6	0.0056 (3)	0.0062 (3)	0.0052 (3)	0.00029 (9)	0	0

Bond lengths (Å) top

Ta1—Ta2a	2.7289 (10)	Ta2b—Ta6ⁱ	2.9245 (13)
Ta1—Ta2aⁱ	2.7289 (10)	Ta2b—Ta6^ix	2.9739 (13)
Ta1—Ta2b	2.7598 (9)	Ta3a—Ta3a^xiv	3.274 (3)
Ta1—Ta2bⁱ	2.7598 (9)	Ta3a—Ta3a^xv	3.242 (3)
Ta1—Ta4ⁱⁱ	3.081 (3)	Ta3a—Ta3a^xvi	2.6844 (14)
Ta1—Ta4ⁱⁱⁱ	3.026 (3)	Ta3a—Ta3a^iv	3.274 (3)
Ta1—Ta4^iv	3.081 (3)	Ta3a—Ta3a^v	3.242 (3)
Ta1—Ta4^v	3.026 (3)	Ta3a—Ta4^xvii	2.8214 (14)
Ta1—Ta5^vi	2.9462 (12)	Ta3a—Ta5^xviii	3.2227 (13)
Ta1—Ta5^vii	2.9462 (12)	Ta3a—Ta5^vi	3.2325 (13)
Ta1—Ta6^viii	2.9235 (11)	Ta3a—Ta6^xviii	3.2146 (13)
Ta1—Ta6^ix	2.9235 (11)	Ta3a—Ta6^viii	3.2244 (13)
Ta2a—Ta2bⁱ	2.7950 (12)	Ta3b—Ta3bⁱⁱ	3.271 (3)
Ta2a—Ta3a^x	2.8622 (14)	Ta3b—Ta3bⁱⁱⁱ	3.291 (3)
Ta2a—Ta3aⁱ	2.8819 (13)	Ta3b—Ta3b^xiii	2.7414 (13)
Ta2a—Ta3a^xi	2.911 (3)	Ta3b—Ta3b^xix	3.271 (3)
Ta2a—Ta3a^xii	2.900 (3)	Ta3b—Ta3b^xx	3.291 (3)
Ta2a—Ta4^iv	3.109 (3)	Ta3b—Ta4	2.7791 (13)
Ta2a—Ta4^v	3.103 (3)	Ta3b—Ta5^xiv	3.2106 (14)
Ta2a—Ta5	2.9430 (12)	Ta3b—Ta5ⁱ	3.2087 (14)
Ta2a—Ta5^vii	2.9604 (12)	Ta3b—Ta6^xv	3.2157 (14)
Ta2a—Ta6	2.9461 (12)	Ta3b—Ta6ⁱ	3.2138 (14)
Ta2a—Ta6^ix	2.9635 (12)	Ta4—Ta4^xxi	3.0424 (13)
Ta2b—Ta3b	2.8489 (13)	Ta4—Ta5^xxii	3.3146 (12)
Ta2b—Ta3bⁱⁱ	2.888 (3)	Ta4—Ta5^xiv	3.3358 (12)
Ta2b—Ta3bⁱⁱⁱ	2.879 (3)	Ta4—Ta5ⁱ	3.3019 (12)
Ta2b—Ta3b^xiii	2.8773 (13)	Ta4—Ta6^xxii	3.3092 (12)
Ta2b—Ta4ⁱⁱ	3.128 (3)	Ta4—Ta6^xv	3.3304 (12)
Ta2b—Ta4ⁱⁱⁱ	3.097 (3)	Ta4—Ta6ⁱ	3.2965 (12)
Ta2b—Ta5ⁱ	2.9347 (13)	Ta5—Ta6^xxiii	2.6475
Ta2b—Ta5^vii	2.9839 (13)	Ta5—Ta6	2.6475

Symmetry codes: (i) −x+1, −y, z; (ii) y+1, −x, −z; (iii) y+1, −x, −z+1; (iv) −y, x, −z; (v) −y, x, −z+1; (vi) y, −x+1, −z; (vii) −y+1, x−1, −z; (viii) y, −x+1, −z+1; (ix) −y+1, x−1, −z+1; (x) x+1, y, z; (xi) −y+1, x, −z; (xii) −y+1, x, −z+1; (xiii) −x+1, −y−1, z; (xiv) y, −x, −z; (xv) y, −x, −z+1; (xvi) −x, −y, z; (xvii) x, y+1, z; (xviii) x−1, y, z; (xix) −y, x−1, −z; (xx) −y, x−1, −z+1; (xxi) −x, −y−1, z; (xxii) x−1, y−1, z; (xxiii) x, y, z−1.

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