PREPARATION AND CHARACTERIZATION OF CRYSTALS OF MX- AND MX2-TYPE ARSENIDES OF NIOBIUM AND TANTALUM

Abstract

Phase analytical work on the systems niobium–arsenic and tantalum–arsenic has established the existence of mono- and di-arsenides as the only phases on the arsenic-rich side of the composition 50 atomic % As. Single crystals of these phases were grown by halide vapor transport reactions. The monoarsenides are tetragonal and isostructural. The lattice parameters of NbAs are a = 3.453 ± 0.002 Å, c = 11.672 ± 0.005 Å and of TaAs, a = 3.436 ± 0.002 Å, c = 11.644 ± 0.005 Å. The diarsenides are isostructural and have a C-face centered mono- clinic cell with a = 9.354 ± 0.002 Å, b = 3.381 ± 0.002 Å, c = 7.799 ± 0.002 Å, β = 119°26′ ± 5′ for NbAs2 and a = 9.350 ± 0.002 Å, b = 3.388 ± 0.002 Å, c = 7.760 ± 0.002 Å, β = 119°45′ ± 5′ for TaAs2.