Article pubs.acs.org/IC
Synthesis and Crystal Structure of Suboxide Solid Solutions, Ti12−δGaxBi3−xO10 Shinsaku Amano and Hisanori Yamane* Institute of Multidisciplinary Research for Advanced Materials, Tohoku University 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan S Supporting Information *
ABSTRACT: Single crystals of suboxide solid solutions Ti12−δGaxBi3−xO10 (x = 1.42−1.74; δ = 0.77−0.62) were prepared at 900 °C with a Bi flux. Crystal structure analysis by X-ray diffraction (XRD) revealed that the solid solutions are isostructural with Ti12−δSn3O10 (cubic, space group Fm3̅m). The cell parameter a decreases from 13.5616(3) to 13.5402(5) Å with increasing Ga content, x, while the total valence electron number of Ti12−δGaxBi3−xO10 is maintained at 117.1 by decreasing Ti defects, δ. Stella octangula is formed by sharing of the edges of four supertetrahedra composed of O-centered Ti tetrahedra and trigonal bipyramids (oxide part). Another superpolyhedron is formed by sharing of the pyramidal planes of Ga/Bi-centered, Ti-monocapped square antiprisms (intermetallic part). These two parts are incorporated in the structure. A polycrystalline bulk of a solid solution with x = 2.01 and δ = 0.67 [a = 13.53772(13) Å] was synthesized by reaction sintering at 950 °C from a mixture of Ti, TiO2, Bi2O3, and Ga2O3. The resistivities measured for the bulk were (2.2−2.4) × 10−5 Ω m in the temperature range from 10 to 300 K.
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formed in a Bi flux at 900 °C.19 Ti12−δSn3O10 could not be synthesized by the Bi flux method. However, if Sn(IV) could be replaced with Ga(III) and Bi(V), a compound, Ti12−δ(Ga1/2Bi1/2)3O10, having an equivalent number of valence electrons, would be synthesized by the flux method. The present study reports new solid solutions of Ti12−δGaxBi3−xO10 prepared by the replacement of Sn in Ti12−δSn3O10 with Ga and Bi.
INTRODUCTION In the Ti−O binary system, TiO2, which has the highest valence of IV, and other various suboxides with lower valences have been investigated.1 Single crystals of the Ti−O suboxides have been grown by arc melting and by chemical vapor transport.2 There are a great variety of ternary and quaternary compounds containing Ti(IV), and many dielectric, piezoelectric, ferroelectric, ion-exchange, and electrode materials have been synthesized from Ti(IV)-containing compounds. On the other hand, there are few ternary and quaternary suboxides containing Ti with valences I−III. Representative suboxides are the Ti2Ni-type TiMOx (M = Cr, Mn, Fe, Co, Ni, Cu),3 Ti4M2Ox (x ∼ 1; M = Cr, Mn, Fe, Co, Ni, Cu, Zn, Rh, Ir, Pd, Pd), 4−12 Ti 2 Zr 6 Ni 4 O 0.6 , Ti 2 Zr 6 Co 4 O 0.6 , 13 Ti 3 NiAl 2 O, 14 Ti2Zr6Ni4O0.6, Ti2Zr6Co4O0.6,13 and Ti3NiAl2O14 and the antiperovskite-type Ti3PdO.12 In these suboxides, the O contents are the lowest among the constituent elements. In 1999, Hillebrecht and Ade reported the synthesis and crystal structure of an O-rich suboxide, Ti12−δSn3O10 (δ = 0.69, 15 cubic, a = 13.5652 (9) Å, space group Fm3m ̅ ). The crystal structure was a new type and was characterized by a combination of Ti−O oxide and Ti−Sn intermetallic features. Single crystals of this compound were prepared by heating a mixture of Ti, Al, and Sn at 1500 °C. A new compound having the same structure type had not been found for more than 10 years. Recently, however, new ternary titanium suboxides, Ba1+δTi13−δO12 (δ = 0.11)16 and Ti8BiO7,17 and a new polymorph of monosuboxide, ε-TiO,18 have been prepared in the forms of single crystals by using a Bi flux. In the study of Sn−Bi substitution in Ti 8 BiO 7 , single crystals of Ti11.17(Sn0.85Bi0.15)3O10, isotypic with Ti12−δSn3O10, were © 2017 American Chemical Society
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EXPERIMENTAL SECTION
Starting materials were Bi powder (Mitsuwa Chemicals, 99.999%), Bi2O3 powder (Mitsuwa Chemicals, 99.999%), Ti powder (for singlecrystal growth, Mitsuwa Chemicals, 99.99%,
