Solution Synthesis and Diffusion-Mediated Formation Pathway of NbTe Particles.

NbTe is an important material because of its fundamental low-temperature electronic behavior and its potential interest for thermoelectric, catalytic, and phase-change applications, especially as nano- and microscale particles. As a tellurium-rich group V transition metal telluride, bulk NbTe is typically synthesized through high-temperature solid-state or metal flux reactions and NbTe films can be made by sputtering and annealing, but NbTe is generally not amenable to the lower-temperature solution-based syntheses that yield small particles. Here, we demonstrate a solvothermal route to NbTe particles that is based on mainstream colloidal nanoparticle synthesis. We find that the reaction proceeds through a multistep pathway that begins by first forming elemental tellurium needles. NbTe then deposits on the surface of the tellurium needles through a diffusion-based process. Time-point studies throughout the reaction reveal that crystallographic relationships between Te and NbTe define how the diffusion-based reaction proceeds and help to rationalize the morphology of the resulting NbTe particles. As synthesized, NbTe particles exhibit a surface consisting of predominantly Nb-Te and reduced NbO species, but after storage, surface oxidation transforms these species to primarily NbO and TeO, while the NbTe remains unchanged. These synthetic capabilities and reaction pathway insights for NbTe, made using a solvothermal method, will help to advance future studies on the properties and applications of this and related tellurides.