WO2 triggered nucleation and growth of ultra-long W18O49 structures, from nanobundles to single-crystalline microrod

Abstract W18O49 has exceptional electronic and electro-chromic properties and has been synthesized in various morphologies for applications in nanodevices. Nevertheless, the controlled growth of nanostructured W18O49 with desirable morphology is not yet achieved, and the growth mechanism is not yet clear. In this work, we synthesized ultra-long single-crystalline W18O49 micron-rods via heating W matrix under an atmosphere-Ar flow, and systematically investigated the nucleation and growth by detailed microstructural characterization. The presence of WO2 interlayer above the W matrix was reported for the first time, which was confirmed to play a key role in the epitaxial nucleation of W18O49. Extensive annealing led to the growth of WO2 grain and W18O49 nanostructures into micron-rods, which suggests that W18O49 diameter is controlled by WO2 grain size. This study is helpful in the design of W18O49 nanostructures for various applications.