Abstract
Nanowire crystals of a tantalum nitride phase have been grown from epsilon-tantalum nitride and ammonium halide precursors at high pressures exceeding several gigapascals. Synchrotron x-ray diffraction and Transmission Electron Microscopy (TEM) observations revealed that they had crystallized in an unreported hexagonal structure with lattice parameters of a = 3.050(1) Å and c = 2.909(2) Å. The one-dimensional growth orientation was along the crystallographic [001] direction. Scanning TEM–EDX elemental analyses showed that the nanowire crystals were composed of tantalum and nitrogen with small amounts of oxygen. The presence of the melted ammonium halides combined with supercritical ammonia acting as a reactive flux at high pressure and temperature played a significant role in the nanowire crystal growth. Raman spectroscopy performed on several single crystal nanowires pointed toward metallic properties, and the temperature dependence of the magnetization measured by Superconducting Quantum Interference Device magnetometry suggested a superconducting transition about 6.2 K. The analysis of the compression behavior revealed an incompressible nature, and the bulk modulus was determined to be 363(6) GPa.
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