Synthesis and material properties of polymer-derived niobium carbide and niobium nitride nanocrystalline ceramics

Abstract

Abstract Nanocrystalline niobium carbide (NbC) ceramics and niobium carbide-niobium nitride (NbC/NbN) composites were synthesized at low temperatures without high-pressure sintering using a single-step polymer-derived approach from a meltable pre-ceramic blend. Niobium hydride (NbH5) and 1,2,4,5-tetrakis(phenylethynyl)benzene (TPEB) reacted at 1500\xa0°C under argon or nitrogen in a tube furnace to form NbC or NbC/NbN with high purities and nanosized grains. Superconductivity measurements indicated that NbC/NbN ceramics exhibited a mixed phase system with two distinct Tc values, and higher elemental niobium content within solids yielded lower Tc. The resulting ceramic monoliths exhibited homogeneous morphologies and controllable amounts of free carbon in the composite matrix. Niobium carbide and nitride composites demonstrated good air oxidation stability up to 450\xa0°C.