Superconducting tantalum disulfide nanotapes; growth, structure and stoichiometry

Abstract

Superconducting tantalum disulfidenanowires have been synthesised by surface-assisted chemical vapour transport (SACVT) methods and their crystal structure, morphology and stoichiometry studied by powder X-ray diffraction (PXD), scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and nanodiffraction. The evolution of morphology, stoichiometry and structure of materials grown by SACVT methods in the Ta–S system with reaction temperature was investigated systematically. High-aspect-ratio, superconducting disulfidenanowires are produced at intermediate reaction temperatures (650 °C). The superconducting wires are single crystalline, adopt the 2H polytypic structure (hexagonal space group P6₃/mmc: a = 3.32(2) Å, c = 12.159(2) Å; c/a = 3.66) and grow in the <20> direction. The nanowires are of rectangular cross-section forming nanotapes composed of bundles of much smaller fibres that grow cooperatively. At lower reaction temperatures nanowires close to a composition of TaS₃ are produced whereas elevated temperatures yield platelets of 1T TaS₂.