Experimental Study of the Binary Nb-Te System

Transition metal dichalcogenides have been receiving considerable attention in the literature due to their great variety of physical properties. Recently, some compounds of this family have been pointed out as new examples of Dirac and Weyl semimetals. However, the lack of thermodynamic data or experimental studies on these binary systems makes the synthesis of high-quality samples purely empirical. This report investigates the binary Nb-Te phase diagram. Results of x-ray diffraction, Rietveld refinement, scanning electron microscopy, and differential thermal analysis strongly suggest that Nb5Te4 and Nb3Te4 are stable only at high temperatures. These phases decompose according to the following eutectoid reactions: Nb3Te4(s)→ Nbss + NbTe2(s) at 735 °C and Nb5Te4(s)→ Nbss + Nb3Te4(s) at 839 °C. Furthermore, the results presented in this study show that NbTe2 and NbTe4 are the only stable compounds in the Te-rich portion of the phase diagram (> 60 at.% of Te) at temperatures below 735 °C.