Exploring the Morphology Control and Formation Mechanisms of Ultra-High Temperature Ceramic Particles: A Study on Tantalum Carbide
Tantalum carbide (TaC) belongs to a class of materials known as ultra-high temperatureceramics (UHTCs) with unique combinations of physical, chemical and electronic properties. The following study presents for the first time the morphologically controlled synthesis of TaC nanoparticles using a modified solvothermal method. X-ray diffraction revealed that highly crystalline TaC can be obtained with excellent phase purity. Doping by metallic species is shown to have significant impact on the final morphology of TaC nanoparticles. The shape selectivity and morphology evolution from round/irregular shapes to cubes and cuboctahedrons varies with the type of dopant, including Ni, Fe, Co, Y and Ni-Ti co-doping. Statistical abundance of over 80% particles with high-faceted morphologies were observed, significantly surpassing that of undoped samples (around 10%). Experimental interpretation was coupled by the Density Functional Theory (DFT) based calculation to probe the fundamental mechanisms responsible for the dopant-induced change in the growth habit of TaC nanoparticles. It was found that the major formation mechanisms include surface segregation of dopants, atomic orbital interaction between dopants and carbon, which caused the change in relative growth rate of facets. The probability of forming one type of faceted particles over another is governed by the surface energy distributions. The mechanisms and techniques explored herein are expected to be generally applicable to other transition metal-based ceramics thereby providing an unprecedented pathway towards the morphology tailoring of high-temperature materials. Principles of crystal growth and prior works for morphologically controlled synthesis of a variety of inorganic materials were also thoroughly reviewed.