Structure and Crystal Chemistry of M0.5Ta0.5B (M = Ti, Zr, and Hf)
I Talmy, J Zaykoski, J A. Kudak, Winnie Wong-Ng
During the development of refractory composites (cermets) combining MB2 (M=Ti, Zr, or Hf) ceramics and Ta metal, three new phases of compositions M0.5Ta0.5B were discovered. Preliminary determination of lattice parameters using x-ray powder diffraction indicated that the structure of the new phases to be isostrucural with FeB (orthorhombic Pnma). The final FeB-type structure was confirmed using the x-ray Rietveld refinement technique. The lattice parameters were found to be a=6.12969(6) , b=3.08700(4) , c=4.63558(7) , and V= 87.716(2) 3 for Ti0.5Ta0.5B, a=6.27439(8) , b=3.16370(4) , c=4.78060(7) , and V= 94.897(3) 3 for Zr0.5Ta0.5B, and a=6.30325(8) , b=3.15748(6) , c=4.79499(6) , and V= 95.432(2) 3 for Hf0.5Ta0.5B. In the M0.5Ta0.5B (M=Ti, Zr, or Hf) structure, Ta was found to share the same metallic site of Ti, Zr and Hf in a disordered fashion. The structure is characterized by trigonal prisms and quadrilateral channels of (M,Ta) throughout the lattice. Zigzag chains of boron were found running parallel to the b-direction in the quadrilateral channels. Each boron site is surrounded by seven (M,Ta) sites with distances ranging from 2.272(6) to 2.606(6) for Ti0.5Ta0.5B, 2.271(4) to 2.665(6) for Zr0.5Ta0.5B, and 2.223(4) to 2.720(6) for Hf0.5Ta0.5B. Each metal site is surrounded by 10 metal neighbors, ranging from 2.9303(3) A to 3.2801(3) for Ti0.5Ta0.5B, 2.9612(6) to 3.3556(2)A for Zr0.5Ta0.5B, and 2.9787(6) to 3.37808(2) for Hf0.5Ta0.5B. Reference x-ray powder patterns for these three phases were prepared and were submitted to the International Centre for Diffraction Data (ICDD) to be included in the Powder Diffraction File (PDF).
, Zaykoski, J.
, Kudak, J.
and Wong-Ng, W.
Structure and Crystal Chemistry of M<sub>0.5</sub>Ta<sub>0.5</sub>B (M = Ti, Zr, and Hf), Acta Crystallographica Section B-Structural Science
(Accessed December 4, 2023)