Abstract
The flux growth method was successfully employed to synthesize millimeter-sized single crystals of the ternary barium vanadium pnictides Ba(5)V(12)As(19+x) (x ≈ 0.02) and Ba(5)V(12)Sb(19+x) (x ≈ 0.36), using molten Pb and Sb, respectively. Both compositions crystallize in space group P 4¯ 3m and adopt a structure similar to those of the barium titanium pnictides Ba(5)Ti(12) Pn (19+x) (Pn = Sb, Bi), yet with a subtly different disorder, involving the pnictogen and barium atoms. Attempts to obtain an arsenide analog of Ba(5)Ti(12) Pn (19+x) using a Pb flux technique yielded binary arsenides. High-temperature treatment of the elements Ba, Ti, and As in Nb or Ta tubes resulted in side reactions with the crucible materials and produced two isostructural compositions Ba(8)Ti(13-x) M (x) As(21) (M = Nb, Ta; x ≈ 4), representing a new structure type. The latter structure displays fcc-type metal clusters comprised of statistically distributed Ti and M atoms (M = Nb, Ta) with multi-center and two-center bonding within the clusters, as suggested by our first-principle calculations.