Rapid and Scalable Synthesis, Structure, and Physical Properties of Solid-Solution Layered Titanium Niobium Carbosulfide “Ti x Nb2– x SC”

Abstract

We demonstrate rapid, scalable synthesis of solid-solution layered transition metal carbosulfides, TixNb2–xSC (0 ≤ x ≤ 2). Thermogravimetric analysis confirmed superior thermal stability of Ti2SC vs Nb2SC; oxidation of Nb2SC in air (750 °C) produced an accordion-like sulfur-bearing niobium oxide. Room-temperature X-ray diffraction and temperature-dependent neutron diffraction revealed linear contraction of lattice parameters with increasing Ti content. Strong anisotropic thermal expansion behavior arises from metallic basal planes vs nonmetallic M–S bonds, with Nb2SC showing larger volumetric expansion than Ti2SC. Specific heat measurments confirm that Ti2SC is stiffer than Nb2SC. In both thermal expansion and specific heat, nonmonotonic behaviors are linked to the critical role of Ti/Nb mixing. SQUID measurements show diamagnetic shielding in high-Nb samples, which, lacking an anomaly in specific heat, is ascribed to trace, percolating superconducting impurities rather than bulk superconductivity.