Crystal structure of Ti8Bi9O0.25 containing inter­stitial oxygen atoms

Yamane, H.; Hiraka, K.

doi:10.1107/S205698901801188X

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ISSN: 2056-9890

Volume 74| Part 9| September 2018| Pages 1366-1368

https://doi.org/10.1107/S205698901801188X

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Crystal structure of Ti₈Bi₉O_0.25 containing interstitial oxygen atoms

Hisanori Yamane ^a ^* and Keita Hiraka ^a

^aInstitute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan
^*Correspondence e-mail: hisanori.yamane.a1@tohoku.ac.jp

Edited by M. Weil, Vienna University of Technology, Austria (Received 22 July 2018; accepted 21 August 2018; online 24 August 2018)

Single crystals of Ti₈Bi₉O_0.25, titanium bismuth oxide (8/9/0.25), were obtained from a sample prepared by heating a mixture of Ti, TiO₂ and Bi powders in an Ar atmosphere. Single-crystal X-ray analysis revealed that the introduction of O atoms into the structure of Ti₈Bi₉ retains the space-group type P4/nmm. The oxygen site is located within a Ti₄ tetrahedron (point group symmetry $[\overline{4}]$ m2) that is vacant in the Ti₈Bi₉ crystal structure. The occupancy of this site is 0.25 (4), and the O—Ti distance is 1.8824 (11) Å.

Keywords: titanium bismuth oxygen; Bi flux growth; crystal structure; interstitial site.

CCDC reference: 1863407

1. Chemical context

The crystal structure of Ti₈Bi₉, having the tetragonal space group P4/nmm, a = 10.277 (1) Å, c = 7.375 (1) Å, Z = 2, was determined by Richter and Jeitschko (1997 ). This compound was identified in Ti–Bi binary phase diagrams (Okamoto, 2010 , 2015 ), and was also confirmed by powder X-ray diffraction (PXRD) in a study of the Ti–Bi phase diagram (Maruyama et al., 2013 ). Recently, the use of a Bi flux has enabled single-crystal growth of a new polymorph of TiO (∊-phase; Amano et al., 2016 ) and some new suboxides: Ti₈(Sn_xBi_1–x)O₇, Ti_11.17(Sn_0.85Bi_0.15)₃O₁₀ and Ti_12–δGa_xBi_3–xO₁₀ (Amano & Yamane, 2017 ; Yamane & Amano, 2017 ). While exploring new suboxides containing Ti using a Bi flux, we also found the title compound, Ti₈Bi₉O_0.25 where interstitial O sites are partly occupied.

In the present communication, details of single-crystal growth of Ti₈Bi₉O_0.25 and its comparison with the crystal structure of Ti₈Bi₉ (Richter & Jeitschko, 1997) are reported.

2. Structural commentary

Reflections from a single crystal of Ti₈Bi₉O_0.25 could be indexed with a primitive tetragonal cell similar to that of the oxygen-free compound Ti₈Bi₉ (Richter & Jeitschko, 1997). The differences in the lengths of the a and c axes and in the cell volume from those of Ti₈Bi₉ were +1.0%, −0.09% and +0.74%, respectively. The reflection conditions observed for the new compound were the same as for Ti₈Bi₉, revealing space group P4/nmm.

The crystal structure and atomic arrangement for Ti₈Bi₉O_0.25 are depicted in Figs. 1 and 2, respectively. In the crystal structure of Ti₈Bi₉ (Richter & Jeitschko, 1997), the Ti2 site is in a trigonal antiprism (point group symmetry. .2/m) made up from Bi atoms with Bi—Ti distances of 2.848 (1) and 2.931 (1) Å (Table 1). The Ti3 and Ti4 sites are situated in square antiprisms in which the Bi—Ti distances range from 2.937 (5) to 3.144 (6) Å. The Ti3- and Ti4-centered Bi1₄Bi2₄ square antiprisms both exhibit point group symmetry 4mm and are arranged along the c axis by sharing the square planes. The Bi1Bi2₂ triangle plane is shared by the Ti2-centered Bi1₂Bi2₄ trigonal antiprism and the Ti3-centered Bi1₄Bi2₄ square antiprism. In the crystal structure of Ti₈Bi₉, only the Ti1 site forms a Ti polyhedron. The Ti1—Ti1 distances of the Ti1₄ tetrahedron are 2.934 (6) and 3.074 (3) Å. In addition to the three Ti1 sites, each Ti1 site is surrounded by six Bi atoms at distances of 2.945 (4)–3.074 (5) Å, and by two Ti2 sites at a distance of 3.017 (2) Å. The O atom of Ti₈Bi₉O_0.25 is located in the Ti1₄ tetrahedron at a site with symmetry $[\overline{4}]$ m2 and with a site occupancy of 0.25 (4). The partial occupation by the O atoms changes the Ti1—Ti1 distances in the tetrahedron to 2.992 (2) and 3.1142 (19) Å, representing increases of 1.9% and 1.3%, respectively. The Ti1—Bi2 distance is also increased by 1.4%, although the changes in the Ti3—Bi and Ti4—Bi distances are both less than 0.4%.

Table 1
Selected interatomic distances (Å) for Ti₈Bi₉ (Richter & Jeitschko, 1997) and Ti₈Bi₉O_0.25 (this study)

	Ti₈Bi₉	Ti₈Bi₉O_0.25
Ti1—Ti1	2.934 (6)	2.992 (2)
Ti1—Ti1	3.074 (3) × 2	3.1142 (19) × 2
Ti1—Ti2	3.017 (2) × 2	3.0228 (6) × 2
Ti1—Bi1	2.971 (4) × 2	2.9610 (9) × 2
Ti1—Bi2	2.848 (1)	2.8305 (11)
Ti1—Bi2	3.074 (5) × 2	3.1175 (6) × 2
Ti1—Bi3	2.945 (4)	2.9491 (11)
Ti2—Bi1	2.848 (1) × 2	2.8488 (2) × 2
Ti2—Bi2	2.931 (1) × 4	2.94278 (11) × 4
Ti3—Bi1	3.122 (6) × 4	3.1227 (16) × 4
Ti3—Bi2	3.144 (6) × 4	3.1434 (16) × 4
Ti4—Bi1	2.937 (5) × 4	2.9398 (13) × 4
Ti4—Bi2	2.985 (5) × 4	2.9771 (13) × 4
O1—Ti1		1.8824 (11) × 4

Figure 1
Crystal structure of Ti₈Bi₉O_0.25 drawn with Ti- and O-centered Bi polyhedra. The red part of the O1 sphere in the Ti1₄ tetrahedron shows the occupancy.

Figure 2
Atomic arrangement around Ti and Bi atoms in the structure of Ti₈Bi₉O_0.25. Displacement ellipsoids are drawn at the 99% probability level. [Symmetry codes: (i) −y, −x + $[{1\over 2}]$ , −z; (ii) y + 1, −x + $[{1\over 2}]$ , z − 1; (iii) −x + $[{1\over 2}]$ , −y + $[{1\over 2}]$ , z − 1; (iv) y, −x + $[{1\over 2}]$ , z; (v) −x + $[{1\over 2}]$ , −y + $[{1\over 2}]$ , z; (vi) −x + $[{1\over 2}]$ , −y + $[{1\over 2}]$ , z − 1; (vii) −x + 1, −y + 1, -z; (viii) −y, x + $[{1\over 2}]$ , −z + 1; (ix) x + $[{1\over 2}]$ , y − $[{1\over 2}]$ , −z; (x) −y + $[{3\over 2}]$ , x, z; (xi) −y + $[{1\over 2}]$ , x, z − 1; (xii) y, −x + $[{1\over 2}]$ , z − 1; (xiii) x + $[{1\over 2}]$ , y − $[{1\over 2}]$ , −z + 1; (xiv) x, y, z − 1; (xv) −y + $[{1\over 2}]$ , x, z.]

The O1—Ti1 distance of 1.8824 (11) Å is intermediate between the sums of ionic radii for Ti³⁺ and O²⁻ (1.91 Å) and Ti²⁺—O²⁻ (1.845 Å), based on ionic radii of 0.67 and 0.605 Å for Ti³⁺ and Ti²⁺, respectively, in sixfold coordination, and an O²⁻ radius of 1.24 Å in fourfold coordination (Shannon, 1976 ). The bond-valence sums (BVSs) calculated for the O1 site in the Ti1₄ tetrahedron using bond-valence parameters (R₀) for Ti⁴⁺ (1.815 Å), Ti³⁺ (1.815 Å) and Ti²⁺ (1.734 Å) and B = 0.37 (Brese & O'Keeffe, 1991 ; Amano & Yamane, 2017) are 3.33, 3.12 and 2.68 valence units (v.u.), respectively. All of these values are considerably greater than the expected valence value of 2 for an O atom, which may suggest that the O1 site is not fully occupied, or that bond-valence parameters for titanium in lower oxidation states (and/or tetrahedral coordination) need revision. Complete occupation of O atoms in tetrahedral sites surrounded by Ti atoms has been reported for the crystal structures of Ti_12-δGa_xBi_3–xO₁₀. In these structures, the Ti—O distances range from 1.957 (3) to 2.291 (3) Å, all of which exceed the value of 1.8824 (11) Å for O1—Ti1 in Ti₈Bi₉O_0.25. The BVSs calculated for the O sites in Ti_12–δGa_xBi_3–xO₁₀ using the parameters for Ti³⁺ and Ti²⁺ were found to be in the ranges 2.18–2.21 and 1.87–1.89 v.u., respectively (Amano & Yamane, 2017).

3. Synthesis and crystallization

A sample containing the title compound was prepared by combining 0.85 mmol Ti powder (99.99%, Mitsuwa Chemical Co., Ltd), 0.125 mol TiO₂ powder (rutile, 99.99%, Rare Metallic Co., Ltd) and 1.5 mmol Bi powder (99.999%, Mitsuwa Chemical Co., Ltd) in an agate mortar and subsequent pressing into a pellet (Ø 6 mm) under atmospheric conditions. The pellet was placed in a Ta boat that was then transferred into a stainless-steel tube and sealed with a cap in an Ar-filled glove box (MBRAUN; O₂ and H₂O < 1 ppm). The sealed stainless-steel tube was heated to 1073 K at a rate of approximately 400 K h⁻¹, maintained at this temperature for 10 h, and subsequently cooled to 723 K at a rate of 10 K h⁻¹. Below 723 K, the sample was cooled to room temperature by shutting off the electric power to the heater of the furnace. The resulting sample was crushed and single-crystal fragments of Ti₈Bi₉O_0.25 were extracted. A single crystal for XRD analysis was sealed in a glass capillary. The crushed sample was also analyzed by electron probe microanalysis (EPMA, JEOL, JXA-8200). Only Bi, Ti and O were found in the bulk. The O concentration was greater than the expected values, indicating that some oxidation had occurred while transferring the specimens to the EPMA instrument. In addition to fragments with a Ti:Bi atomic ratio of approximately 8:9, some Bi-rich (>85%) portions and fragments with a Ti:Bi ratio of approximately 3:2 were also identified.

4. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. The diffraction data of Ti₈Bi₉O_0.25 were initially analyzed using the Ti₈Bi₉ model (Richter & Jeitschko, 1997), and a residual electron density of 8.4 e Å⁻³ was observed at (3/4, 1/4, 0), which corresponds to the 2a site in the Ti1₄ tetrahedron. The O-atom occupancy of this site was refined to be 0.25 (4), resulting in a decrease in R[F² > 2σ (F²)] from 0.045 to 0.020. For this site an isotropic atomic displacement parameter was considered.

Table 2
Experimental details

Crystal data
Chemical formula	Ti₈Bi₉O_0.25
M_r	2267.94
Crystal system, space group	Tetragonal, P4/nmm
Temperature (K)	301
a, c (Å)	10.3198 (2), 7.3684 (1)
V (Å³)	784.72 (3)
Z	2
Radiation type	Mo Kα
μ (mm⁻¹)	104.26
Crystal size (mm)	0.10 × 0.08 × 0.06

Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Numerical (SADABS; Krause et al., 2015 )
T_min, T_max	0.011, 0.075
No. of measured, independent and observed [I > 2σ(I)] reflections	14767, 1101, 1079
R_int	0.059
(sin θ/λ)_max (Å⁻¹)	0.833

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.020, 0.044, 1.36
No. of reflections	1101
No. of parameters	34
Δρ_max, Δρ_min (e Å⁻³)	1.55, −1.61
Computer programs: APEX3 and SAINT (Bruker, 2015 ), SHELXT (Sheldrick, 2015a ), SHELXL2014 (Sheldrick, 2015b ), VESTA (Momma & Izumi, 2011 ) and publCIF (Westrip, 2010 ).

Supporting information

CCDC reference: 1863407

Crystal structure: contains datablocks I, Ti8Bi9O0.25. DOI: https://doi.org/10.1107/S205698901801188X/wm5456sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S205698901801188X/wm5456Isup4.hkl

checkCIF report

Computing details top

Data collection: APEX3 (Bruker, 2015); cell refinement: SAINT (Bruker, 2015); data reduction: SAINT (Bruker, 2015); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015b); molecular graphics: VESTA (Momma & Izumi, 2011); software used to prepare material for publication: publCIF (Westrip, 2010).

Titanium bismuth oxide (8/9/0.25) top

Crystal data top

Ti₈Bi₉O_0.25	D_x = 9.598 Mg m⁻³
M_r = 2267.94	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, P4/nmm	Cell parameters from 9927 reflections
a = 10.3198 (2) Å	θ = 2.8–36.3°
c = 7.3684 (1) Å	µ = 104.26 mm⁻¹
V = 784.72 (3) Å³	T = 301 K
Z = 2	Granule, black
F(000) = 1850	0.10 × 0.08 × 0.06 mm

Data collection top

Bruker APEXII CCD diffractometer	1101 independent reflections
Radiation source: micro focus sealed tube	1079 reflections with I > 2σ(I)
Detector resolution: 7.4074 pixels mm^-1	R_int = 0.059
ω– and φ–scans	θ_max = 36.3°, θ_min = 2.8°
Absorption correction: numerical (SADABS; Krause et al., 2015)	h = −17→17
T_min = 0.011, T_max = 0.075	k = −16→17
14767 measured reflections	l = −11→12

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	w = 1/[σ²(F_o²) + 5.5451P] where P = (F_o² + 2F_c²)/3
R[F² > 2σ(F²)] = 0.020	(Δ/σ)_max < 0.001
wR(F²) = 0.044	Δρ_max = 1.55 e Å⁻³
S = 1.36	Δρ_min = −1.61 e Å⁻³
1101 reflections	Extinction correction: SHELXL2014 (Sheldrick, 2015b), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
34 parameters	Extinction coefficient: 0.00132 (8)

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

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

	x	y	z	U_iso*/U_eq	Occ. (<1)
Ti1	0.2500	0.60505 (11)	0.15508 (15)	0.00985 (18)
Ti2	0.0000	0.0000	0.0000	0.0082 (2)
Ti3	0.2500	0.2500	0.0782 (3)	0.0161 (4)
Ti4	0.2500	0.2500	0.5769 (3)	0.0094 (3)
Bi1	0.08500 (2)	0.08500 (2)	0.34804 (3)	0.00996 (6)
Bi2	0.2500	0.01379 (2)	0.80886 (3)	0.00990 (6)
Bi3	0.7500	0.2500	0.5000	0.01392 (9)
O1	0.7500	0.2500	0.0000	0.001 (6)*	0.25 (4)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Ti1	0.0095 (4)	0.0098 (4)	0.0102 (4)	0.000	0.000	−0.0005 (3)
Ti2	0.0073 (3)	0.0073 (3)	0.0099 (6)	0.0006 (4)	0.0002 (3)	0.0002 (3)
Ti3	0.0180 (6)	0.0180 (6)	0.0122 (9)	0.000	0.000	0.000
Ti4	0.0081 (5)	0.0081 (5)	0.0119 (8)	0.000	0.000	0.000
Bi1	0.01015 (7)	0.01015 (7)	0.00956 (10)	−0.00054 (6)	−0.00099 (4)	−0.00099 (4)
Bi2	0.00785 (9)	0.01194 (10)	0.00990 (10)	0.000	0.000	0.00110 (6)
Bi3	0.01626 (13)	0.01626 (13)	0.00924 (17)	0.000	0.000	0.000

Geometric parameters (Å, º) top

Ti1—O1ⁱ	1.8824 (11)	Ti4—Bi1^v	2.9398 (13)
Ti1—Bi2ⁱⁱ	2.8305 (11)	Ti4—Bi1	2.9399 (13)
Ti1—Bi3ⁱⁱⁱ	2.9491 (11)	Ti4—Bi2^xviii	2.9771 (13)
Ti1—Bi1^iv	2.9610 (9)	Ti4—Bi2^v	2.9771 (13)
Ti1—Bi1^v	2.9610 (9)	Ti4—Bi2^iv	2.9771 (13)
Ti1—Ti1^vi	2.992 (2)	Ti4—Bi2	2.9771 (13)
Ti1—Ti2^iv	3.0228 (6)	Bi1—Ti1^xviii	2.9610 (9)
Ti1—Ti2^v	3.0227 (6)	Bi1—Ti1^v	2.9610 (9)
Ti1—Ti1^vii	3.1142 (19)	Bi1—Bi1^xiv	3.3423 (4)
Ti1—Ti1^viii	3.1142 (19)	Bi1—Bi1^iv	3.4054 (3)
Ti1—Bi2^ix	3.1175 (6)	Bi1—Bi1^xviii	3.4054 (3)
Ti1—Bi2^x	3.1175 (6)	Bi2—Ti1^xx	2.8305 (11)
Ti2—Bi1	2.8488 (2)	Bi2—Ti2^xxi	2.9428 (1)
Ti2—Bi1^xi	2.8488 (2)	Bi2—Ti2^xxii	2.9428 (1)
Ti2—Bi2^xii	2.9428 (1)	Bi2—Ti1^xxiii	3.1175 (6)
Ti2—Bi2^xiii	2.9428 (1)	Bi2—Ti1^xxiv	3.1175 (6)
Ti2—Bi2^xiv	2.9428 (1)	Bi2—Ti3^xxii	3.1434 (16)
Ti2—Bi2^xv	2.9428 (1)	Bi2—Bi2^xviii	3.4474 (3)
Ti2—Ti1^xvi	3.0228 (6)	Bi2—Bi2^iv	3.4474 (3)
Ti2—Ti1^v	3.0228 (6)	Bi2—Bi3^xxv	3.5482 (2)
Ti2—Ti1^xvii	3.0228 (6)	Bi3—Ti1^iv	2.9491 (11)
Ti2—Ti1^xviii	3.0228 (6)	Bi3—Ti1ⁱⁱⁱ	2.9491 (11)
Ti3—Bi1^v	3.1227 (16)	Bi3—Ti1^xxvi	2.9491 (11)
Ti3—Bi1^iv	3.1227 (16)	Bi3—Ti1^xxvii	2.9491 (11)
Ti3—Bi1^xviii	3.1227 (16)	Bi3—Bi2^xxviii	3.5482 (2)
Ti3—Bi1	3.1228 (16)	Bi3—Bi2^xxv	3.5482 (2)
Ti3—Bi2^xiii	3.1434 (16)	Bi3—Bi2^xxix	3.5482 (2)
Ti3—Bi2^xv	3.1434 (16)	Bi3—Bi2^xviii	3.5482 (2)
Ti3—Bi2ⁱⁱ	3.1434 (16)	O1—Ti1^xxvii	1.8824 (11)
Ti3—Bi2^xix	3.1434 (16)	O1—Ti1^xxx	1.8824 (11)
Ti4—Bi1^iv	2.9398 (13)	O1—Ti1^iv	1.8824 (11)
Ti4—Bi1^xviii	2.9398 (13)	O1—Ti1ⁱ	1.8824 (11)

O1ⁱ—Ti1—Bi2ⁱⁱ	78.30 (4)	Bi2^xv—Ti3—Bi2^xix	66.51 (4)
O1ⁱ—Ti1—Bi3ⁱⁱⁱ	96.90 (4)	Bi2ⁱⁱ—Ti3—Bi2^xix	66.51 (4)
Bi2ⁱⁱ—Ti1—Bi3ⁱⁱⁱ	175.19 (4)	Bi1^iv—Ti4—Bi1^xviii	109.99 (7)
O1ⁱ—Ti1—Bi1^iv	144.872 (13)	Bi1^iv—Ti4—Bi1^v	70.79 (4)
Bi2ⁱⁱ—Ti1—Bi1^iv	98.38 (3)	Bi1^xviii—Ti4—Bi1^v	70.79 (4)
Bi3ⁱⁱⁱ—Ti1—Bi1^iv	85.54 (3)	Bi1^iv—Ti4—Bi1	70.79 (4)
O1ⁱ—Ti1—Bi1^v	144.872 (13)	Bi1^xviii—Ti4—Bi1	70.79 (4)
Bi2ⁱⁱ—Ti1—Bi1^v	98.38 (3)	Bi1^v—Ti4—Bi1	109.99 (7)
Bi3ⁱⁱⁱ—Ti1—Bi1^v	85.54 (3)	Bi1^iv—Ti4—Bi2^xviii	143.472 (1)
Bi1^iv—Ti1—Bi1^v	70.21 (3)	Bi1^xviii—Ti4—Bi2^xviii	81.667 (5)
O1ⁱ—Ti1—Ti1^vi	37.37 (3)	Bi1^v—Ti4—Bi2^xviii	81.667 (5)
Bi2ⁱⁱ—Ti1—Ti1^vi	115.67 (2)	Bi1—Ti4—Bi2^xviii	143.471 (2)
Bi3ⁱⁱⁱ—Ti1—Ti1^vi	59.52 (2)	Bi1^iv—Ti4—Bi2^v	81.667 (5)
Bi1^iv—Ti1—Ti1^vi	131.482 (19)	Bi1^xviii—Ti4—Bi2^v	143.472 (1)
Bi1^v—Ti1—Ti1^vi	131.482 (19)	Bi1^v—Ti4—Bi2^v	81.667 (5)
O1ⁱ—Ti1—Ti2^iv	93.18 (3)	Bi1—Ti4—Bi2^v	143.471 (1)
Bi2ⁱⁱ—Ti1—Ti2^iv	60.259 (18)	Bi2^xviii—Ti4—Bi2^v	70.76 (4)
Bi3ⁱⁱⁱ—Ti1—Ti2^iv	120.510 (18)	Bi1^iv—Ti4—Bi2^iv	81.667 (5)
Bi1^iv—Ti1—Ti2^iv	56.850 (12)	Bi1^xviii—Ti4—Bi2^iv	143.472 (1)
Bi1^v—Ti1—Ti2^iv	115.77 (3)	Bi1^v—Ti4—Bi2^iv	143.472 (1)
Ti1^vi—Ti1—Ti2^iv	111.02 (2)	Bi1—Ti4—Bi2^iv	81.667 (5)
O1ⁱ—Ti1—Ti2^v	93.18 (3)	Bi2^xviii—Ti4—Bi2^iv	109.93 (7)
Bi2ⁱⁱ—Ti1—Ti2^v	60.259 (18)	Bi2^v—Ti4—Bi2^iv	70.76 (4)
Bi3ⁱⁱⁱ—Ti1—Ti2^v	120.510 (18)	Bi1^iv—Ti4—Bi2	143.472 (1)
Bi1^iv—Ti1—Ti2^v	115.77 (3)	Bi1^xviii—Ti4—Bi2	81.668 (5)
Bi1^v—Ti1—Ti2^v	56.850 (12)	Bi1^v—Ti4—Bi2	143.472 (2)
Ti1^vi—Ti1—Ti2^v	111.02 (2)	Bi1—Ti4—Bi2	81.667 (5)
Ti2^iv—Ti1—Ti2^v	117.19 (4)	Bi2^xviii—Ti4—Bi2	70.76 (4)
O1ⁱ—Ti1—Ti1^vii	34.188 (17)	Bi2^v—Ti4—Bi2	109.93 (7)
Bi2ⁱⁱ—Ti1—Ti1^vii	63.05 (3)	Bi2^iv—Ti4—Bi2	70.76 (4)
Bi3ⁱⁱⁱ—Ti1—Ti1^vii	112.88 (4)	Ti2—Bi1—Ti4	150.82 (4)
Bi1^iv—Ti1—Ti1^vii	113.225 (13)	Ti2—Bi1—Ti1^xviii	62.668 (16)
Bi1^v—Ti1—Ti1^vii	161.22 (5)	Ti4—Bi1—Ti1^xviii	109.028 (19)
Ti1^vi—Ti1—Ti1^vii	61.29 (2)	Ti2—Bi1—Ti1^v	62.668 (16)
Ti2^iv—Ti1—Ti1^vii	58.99 (2)	Ti4—Bi1—Ti1^v	109.028 (19)
Ti2^v—Ti1—Ti1^vii	107.75 (4)	Ti1^xviii—Bi1—Ti1^v	122.09 (4)
O1ⁱ—Ti1—Ti1^viii	34.188 (17)	Ti2—Bi1—Ti3	76.27 (4)
Bi2ⁱⁱ—Ti1—Ti1^viii	63.05 (3)	Ti4—Bi1—Ti3	74.55 (5)
Bi3ⁱⁱⁱ—Ti1—Ti1^viii	112.88 (4)	Ti1^xviii—Bi1—Ti3	75.04 (2)
Bi1^iv—Ti1—Ti1^viii	161.22 (5)	Ti1^v—Bi1—Ti3	75.04 (2)
Bi1^v—Ti1—Ti1^viii	113.225 (13)	Ti2—Bi1—Bi1^xiv	106.253 (10)
Ti1^vi—Ti1—Ti1^viii	61.29 (2)	Ti4—Bi1—Bi1^xiv	102.93 (4)
Ti2^iv—Ti1—Ti1^viii	107.75 (4)	Ti1^xviii—Bi1—Bi1^xiv	106.02 (2)
Ti2^v—Ti1—Ti1^viii	58.99 (2)	Ti1^v—Bi1—Bi1^xiv	106.02 (2)
Ti1^vii—Ti1—Ti1^viii	57.42 (4)	Ti3—Bi1—Bi1^xiv	177.48 (4)
O1ⁱ—Ti1—Bi2^ix	70.76 (2)	Ti2—Bi1—Bi1^iv	107.934 (3)
Bi2ⁱⁱ—Ti1—Bi2^ix	106.54 (2)	Ti4—Bi1—Bi1^iv	54.606 (18)
Bi3ⁱⁱⁱ—Ti1—Bi2^ix	71.53 (2)	Ti1^xviii—Bi1—Bi1^iv	54.897 (13)
Bi1^iv—Ti1—Bi2^ix	141.17 (3)	Ti1^v—Bi1—Bi1^iv	131.480 (19)
Bi1^v—Ti1—Bi2^ix	76.984 (10)	Ti3—Bi1—Bi1^iv	56.957 (19)
Ti1^vi—Ti1—Bi2^ix	61.325 (18)	Bi1^xiv—Bi1—Bi1^iv	121.663 (4)
Ti2^iv—Ti1—Bi2^ix	161.73 (4)	Ti2—Bi1—Bi1^xviii	107.934 (3)
Ti2^v—Ti1—Bi2^ix	57.249 (4)	Ti4—Bi1—Bi1^xviii	54.606 (18)
Ti1^vii—Ti1—Bi2^ix	104.57 (2)	Ti1^xviii—Bi1—Bi1^xviii	131.480 (19)
Ti1^viii—Ti1—Bi2^ix	54.03 (3)	Ti1^v—Bi1—Bi1^xviii	54.897 (13)
O1ⁱ—Ti1—Bi2^x	70.76 (2)	Ti3—Bi1—Bi1^xviii	56.957 (19)
Bi2ⁱⁱ—Ti1—Bi2^x	106.54 (2)	Bi1^xiv—Bi1—Bi1^xviii	121.663 (4)
Bi3ⁱⁱⁱ—Ti1—Bi2^x	71.53 (2)	Bi1^iv—Bi1—Bi1^xviii	90.0
Bi1^iv—Ti1—Bi2^x	76.984 (10)	Ti1^xx—Bi2—Ti2^xxi	63.110 (6)
Bi1^v—Ti1—Bi2^x	141.17 (3)	Ti1^xx—Bi2—Ti2^xxii	63.110 (6)
Ti1^vi—Ti1—Bi2^x	61.325 (18)	Ti2^xxi—Bi2—Ti2^xxii	122.496 (7)
Ti2^iv—Ti1—Bi2^x	57.249 (5)	Ti1^xx—Bi2—Ti4	150.71 (4)
Ti2^v—Ti1—Bi2^x	161.73 (4)	Ti2^xxi—Bi2—Ti4	108.320 (15)
Ti1^vii—Ti1—Bi2^x	54.03 (3)	Ti2^xxii—Bi2—Ti4	108.320 (14)
Ti1^viii—Ti1—Bi2^x	104.57 (2)	Ti1^xx—Bi2—Ti1^xxiii	62.93 (4)
Bi2^ix—Ti1—Bi2^x	121.67 (4)	Ti2^xxi—Bi2—Ti1^xxiii	109.73 (2)
Bi1—Ti2—Bi1^xi	180.0	Ti2^xxii—Bi2—Ti1^xxiii	59.756 (18)
Bi1—Ti2—Bi2^xii	81.606 (5)	Ti4—Bi2—Ti1^xxiii	139.81 (3)
Bi1^xi—Ti2—Bi2^xii	98.393 (5)	Ti1^xx—Bi2—Ti1^xxiv	62.93 (4)
Bi1—Ti2—Bi2^xiii	98.394 (5)	Ti2^xxi—Bi2—Ti1^xxiv	59.756 (18)
Bi1^xi—Ti2—Bi2^xiii	81.607 (5)	Ti2^xxii—Bi2—Ti1^xxiv	109.73 (2)
Bi2^xii—Ti2—Bi2^xiii	180.0	Ti4—Bi2—Ti1^xxiv	139.81 (3)
Bi1—Ti2—Bi2^xiv	81.606 (5)	Ti1^xxiii—Bi2—Ti1^xxiv	57.35 (4)
Bi1^xi—Ti2—Bi2^xiv	98.393 (5)	Ti1^xx—Bi2—Ti3^xxii	76.52 (4)
Bi2^xii—Ti2—Bi2^xiv	71.710 (9)	Ti2^xxi—Bi2—Ti3^xxii	74.653 (16)
Bi2^xiii—Ti2—Bi2^xiv	108.290 (9)	Ti2^xxii—Bi2—Ti3^xxii	74.653 (16)
Bi1—Ti2—Bi2^xv	98.394 (5)	Ti4—Bi2—Ti3^xxii	74.19 (5)
Bi1^xi—Ti2—Bi2^xv	81.607 (5)	Ti1^xxiii—Bi2—Ti3^xxii	128.56 (3)
Bi2^xii—Ti2—Bi2^xv	108.290 (9)	Ti1^xxiv—Bi2—Ti3^xxii	128.56 (3)
Bi2^xiii—Ti2—Bi2^xv	71.710 (9)	Ti1^xx—Bi2—Bi2^xviii	107.841 (15)
Bi2^xiv—Ti2—Bi2^xv	180.0	Ti2^xxi—Bi2—Bi2^xviii	54.145 (4)
Bi1—Ti2—Ti1^xvi	119.52 (2)	Ti2^xxii—Bi2—Bi2^xviii	130.853 (4)
Bi1^xi—Ti2—Ti1^xvi	60.48 (2)	Ti4—Bi2—Bi2^xviii	54.621 (18)
Bi2^xii—Ti2—Ti1^xvi	117.005 (19)	Ti1^xxiii—Bi2—Bi2^xviii	163.087 (18)
Bi2^xiii—Ti2—Ti1^xvi	62.995 (19)	Ti1^xxiv—Bi2—Bi2^xviii	106.151 (18)
Bi2^xiv—Ti2—Ti1^xvi	56.632 (18)	Ti3^xxii—Bi2—Bi2^xviii	56.746 (19)
Bi2^xv—Ti2—Ti1^xvi	123.369 (18)	Ti1^xx—Bi2—Bi2^iv	107.841 (15)
Bi1—Ti2—Ti1^v	60.48 (2)	Ti2^xxi—Bi2—Bi2^iv	130.853 (4)
Bi1^xi—Ti2—Ti1^v	119.52 (2)	Ti2^xxii—Bi2—Bi2^iv	54.145 (4)
Bi2^xii—Ti2—Ti1^v	62.995 (19)	Ti4—Bi2—Bi2^iv	54.621 (18)
Bi2^xiii—Ti2—Ti1^v	117.005 (19)	Ti1^xxiii—Bi2—Bi2^iv	106.151 (18)
Bi2^xiv—Ti2—Ti1^v	123.369 (18)	Ti1^xxiv—Bi2—Bi2^iv	163.087 (18)
Bi2^xv—Ti2—Ti1^v	56.632 (18)	Ti3^xxii—Bi2—Bi2^iv	56.746 (19)
Ti1^xvi—Ti2—Ti1^v	180.00 (4)	Bi2^xviii—Bi2—Bi2^iv	90.0
Bi1—Ti2—Ti1^xvii	119.52 (2)	Ti1^xx—Bi2—Bi3^xxv	104.22 (2)
Bi1^xi—Ti2—Ti1^xvii	60.48 (2)	Ti2^xxi—Bi2—Bi3^xxv	105.657 (5)
Bi2^xii—Ti2—Ti1^xvii	56.631 (18)	Ti2^xxii—Bi2—Bi3^xxv	105.657 (5)
Bi2^xiii—Ti2—Ti1^xvii	123.369 (18)	Ti4—Bi2—Bi3^xxv	105.07 (4)
Bi2^xiv—Ti2—Ti1^xvii	117.005 (19)	Ti1^xxiii—Bi2—Bi3^xxv	52.029 (19)
Bi2^xv—Ti2—Ti1^xvii	62.995 (19)	Ti1^xxiv—Bi2—Bi3^xxv	52.029 (19)
Ti1^xvi—Ti2—Ti1^xvii	117.99 (4)	Ti3^xxii—Bi2—Bi3^xxv	179.25 (4)
Ti1^v—Ti2—Ti1^xvii	62.01 (4)	Bi2^xviii—Bi2—Bi3^xxv	122.853 (2)
Bi1—Ti2—Ti1^xviii	60.48 (2)	Bi2^iv—Bi2—Bi3^xxv	122.853 (2)
Bi1^xi—Ti2—Ti1^xviii	119.52 (2)	Ti1^iv—Bi3—Ti1ⁱⁱⁱ	137.96 (3)
Bi2^xii—Ti2—Ti1^xviii	123.369 (18)	Ti1^iv—Bi3—Ti1^xxvi	137.96 (3)
Bi2^xiii—Ti2—Ti1^xviii	56.631 (18)	Ti1ⁱⁱⁱ—Bi3—Ti1^xxvi	60.96 (4)
Bi2^xiv—Ti2—Ti1^xviii	62.995 (19)	Ti1^iv—Bi3—Ti1^xxvii	60.96 (4)
Bi2^xv—Ti2—Ti1^xviii	117.005 (19)	Ti1ⁱⁱⁱ—Bi3—Ti1^xxvii	137.96 (3)
Ti1^xvi—Ti2—Ti1^xviii	62.01 (4)	Ti1^xxvi—Bi3—Ti1^xxvii	137.96 (3)
Ti1^v—Ti2—Ti1^xviii	117.99 (4)	Ti1^iv—Bi3—Bi2^xxviii	160.38 (2)
Ti1^xvii—Ti2—Ti1^xviii	180.00 (4)	Ti1ⁱⁱⁱ—Bi3—Bi2^xxviii	56.443 (9)
Bi1^v—Ti3—Bi1^iv	66.09 (4)	Ti1^xxvi—Bi3—Bi2^xxviii	56.443 (9)
Bi1^v—Ti3—Bi1^xviii	66.09 (4)	Ti1^xxvii—Bi3—Bi2^xxviii	99.42 (2)
Bi1^iv—Ti3—Bi1^xviii	100.91 (7)	Ti1^iv—Bi3—Bi2^xxv	56.443 (9)
Bi1^v—Ti3—Bi1	100.91 (7)	Ti1ⁱⁱⁱ—Bi3—Bi2^xxv	160.38 (2)
Bi1^iv—Ti3—Bi1	66.09 (4)	Ti1^xxvi—Bi3—Bi2^xxv	99.42 (2)
Bi1^xviii—Ti3—Bi1	66.09 (4)	Ti1^xxvii—Bi3—Bi2^xxv	56.443 (9)
Bi1^v—Ti3—Bi2^xiii	145.571 (2)	Bi2^xxviii—Bi3—Bi2^xxv	114.292 (4)
Bi1^iv—Ti3—Bi2^xiii	88.805 (5)	Ti1^iv—Bi3—Bi2^xxix	56.443 (9)
Bi1^xviii—Ti3—Bi2^xiii	145.571 (2)	Ti1ⁱⁱⁱ—Bi3—Bi2^xxix	99.42 (2)
Bi1—Ti3—Bi2^xiii	88.805 (5)	Ti1^xxvi—Bi3—Bi2^xxix	160.38 (2)
Bi1^v—Ti3—Bi2^xv	145.571 (2)	Ti1^xxvii—Bi3—Bi2^xxix	56.443 (9)
Bi1^iv—Ti3—Bi2^xv	145.571 (2)	Bi2^xxviii—Bi3—Bi2^xxix	114.292 (4)
Bi1^xviii—Ti3—Bi2^xv	88.805 (5)	Bi2^xxv—Bi3—Bi2^xxix	100.208 (7)
Bi1—Ti3—Bi2^xv	88.805 (5)	Ti1^iv—Bi3—Bi2^xviii	99.42 (2)
Bi2^xiii—Ti3—Bi2^xv	66.51 (4)	Ti1ⁱⁱⁱ—Bi3—Bi2^xviii	56.443 (9)
Bi1^v—Ti3—Bi2ⁱⁱ	88.805 (5)	Ti1^xxvi—Bi3—Bi2^xviii	56.443 (9)
Bi1^iv—Ti3—Bi2ⁱⁱ	88.805 (5)	Ti1^xxvii—Bi3—Bi2^xviii	160.38 (2)
Bi1^xviii—Ti3—Bi2ⁱⁱ	145.571 (2)	Bi2^xxviii—Bi3—Bi2^xviii	100.208 (7)
Bi1—Ti3—Bi2ⁱⁱ	145.571 (2)	Bi2^xxv—Bi3—Bi2^xviii	114.292 (4)
Bi2^xiii—Ti3—Bi2ⁱⁱ	66.51 (4)	Bi2^xxix—Bi3—Bi2^xviii	114.292 (4)
Bi2^xv—Ti3—Bi2ⁱⁱ	101.70 (7)	Ti1^xxvii—O1—Ti1^xxx	111.62 (3)
Bi1^v—Ti3—Bi2^xix	88.805 (5)	Ti1^xxvii—O1—Ti1^iv	105.25 (7)
Bi1^iv—Ti3—Bi2^xix	145.571 (2)	Ti1^xxx—O1—Ti1^iv	111.62 (3)
Bi1^xviii—Ti3—Bi2^xix	88.805 (5)	Ti1^xxvii—O1—Ti1ⁱ	111.62 (3)
Bi1—Ti3—Bi2^xix	145.571 (2)	Ti1^xxx—O1—Ti1ⁱ	105.25 (7)
Bi2^xiii—Ti3—Bi2^xix	101.70 (7)	Ti1^iv—O1—Ti1ⁱ	111.62 (3)

Symmetry codes: (i) −x+1, −y+1, −z; (ii) −x+1/2, −y+1/2, z−1; (iii) −x+1, −y+1, −z+1; (iv) y, −x+1/2, z; (v) −x+1/2, −y+1/2, z; (vi) −x+1/2, −y+3/2, z; (vii) y−1/2, −x+1, −z; (viii) −y+1, x+1/2, −z; (ix) y+1/2, −x+1, −z+1; (x) −y, x+1/2, −z+1; (xi) −x, −y, −z; (xii) −y, x−1/2, −z+1; (xiii) y, −x+1/2, z−1; (xiv) −x, −y, −z+1; (xv) x, y, z−1; (xvi) x−1/2, y−1/2, −z; (xvii) y−1/2, −x, −z; (xviii) −y+1/2, x, z; (xix) −y+1/2, x, z−1; (xx) −x+1/2, −y+1/2, z+1; (xxi) −y+1/2, x, z+1; (xxii) x, y, z+1; (xxiii) y−1/2, −x, −z+1; (xxiv) −y+1, x−1/2, −z+1; (xxv) −x+1, −y, −z+1; (xxvi) x+1/2, y−1/2, −z+1; (xxvii) −y+3/2, x, z; (xxviii) y+1, −x+1/2, z; (xxix) x+1/2, y+1/2, −z+1; (xxx) x+1/2, y−1/2, −z.

Selected interatomic distances (Å) for Ti₈Bi₉ (Richter & Jeitschko, 1997) and Ti₈Bi₉O_0.25 (this study) top

	Ti₈Bi₉	Ti₈Bi₉O_0.25
Ti1—Ti1	2.934 (6)	2.992 (2)
Ti1—Ti1	3.074 (3) × 2	3.1142 (19) × 2
Ti1—Ti2	3.017 (2) × 2	3.0228 (6) × 2
Ti1—Bi1	2.971 (4) × 2	2.9610 (9) × 2
Ti1—Bi2	2.848 (1)	2.8305 (11)
Ti1—Bi2	3.074 (5) × 2	3.1175 (6) × 2
Ti1—Bi3	2.945 (4)	2.9491 (11)
Ti2—Bi1	2.848 (1) × 2	2.8488 (2) × 2
Ti2—Bi2	2.931 (1) × 4	2.94278 (11) × 4
Ti3—Bi1	3.122 (6) × 4	3.1227 (16) × 4
Ti3—Bi2	3.144 (6) × 4	3.1434 (16) × 4
Ti4—Bi1	2.937 (5) × 4	2.9398 (13) × 4
Ti4—Bi2	2.985 (5) × 4	2.9771 (13) × 4
O1—Ti1		1.8824 (11) × 4

Acknowledgements

The authors wish to thank Takashi Kamaya for performing the EPMA analysis.

Funding information

This work was supported in part by a Grant-in-Aid for Scientific Research (B) (No. 16H04494) from the Ministry of Education, Culture, Sports and Technology (MEXT), Japan.

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