Novel Refractory Phase, Ta7Si2(SixB1-x)(2)

Author(s)

Romaka, V. ^[1] ; Fosodeder, V. ^[1] ; Rogl, P. F. ^[1] ; Ramos, E. C. T. ^[2] ; Nunes, C. A. ^[3] ; Coelho, G. C. ^{[3, 4]} ; Giester, G. ^[5]

Affiliation

^[1] Univ Vienna, Inst Phys Chem, A-1090 Vienna - Austria

^[2] Univ Fed Alfenas, BR-37715400 Pocos De Caldas, MG - Brazil

^[3] Univ Sao Paulo, Escola Engn Lorena, Dept Engn Mat DEMAR, BR-12600000 Sao Paulo - Brazil

^[4] Ctr Univ Volta Redonda, BR-27240560 Rio De Janeiro - Brazil

^[5] Univ Vienna, Inst Mineral & Crystallog, A-1090 Vienna - Austria

• Document type: Journal article
• Source: Inorganic Chemistry; v. 52, n. 19, p. 11295-11301, OCT 7 2013.
• Web of Science Citations: 0

Abstract

X-ray single crystal (XSC) and powder diffraction data (XPD) were used to elucidate the crystal structure of a new refractory silicon boride Ta7Si2(SixB1-x)(2) (x = 0.12). Tetragonal Ta7Si2(SixB1-x)(2) (space group P4/mbm; a = 0.62219(2) nm, c = 0.83283(3) nm) with B atoms randomly sharing the 4g site with Si atoms is isotypic with the boride structure of (Re,Co)(7)B-4. The architecture of the structure of Ta7Si2(SixB1-x)(2) combines layers of three-capped triangular metal prisms (Si,B){[}Ta6+2(Si,B)] alternating with double layers of two-capped Si{[}Ta8+1Si] Archimedian metal antiprisms. Consequently, the metal framework contains (B/Si) pairs and Si-Si dumbbells. These two types of coordination figures around the nonmetal atoms are typical for the system-inherent structures of Ta2B (or Ta2Si) and Ta3B2. DFT calculations showed strong B(Si)-B(Si) and Si-Si bonding and represent Ta7Si2(SixB1-x)(2) as a covalent-ionic compound. This bonding behavior is reflected in the high hardness value of 1750 HV. The Sommerfeld constant, gamma = 7.58 mJ/mol K-2, as derived from the electronic density of states, calculated at the Fermi level, suggests typical metallic behavior. (AU)