Growth, Structure, and Stability of KxWO3 Nanorods on Mica Substrate

KxWO3 nanorods, interesting as gas sensors, were elaborated on mica muscovite substrate and characterized by atomic force microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and mainly transmission electron microscopy. A combination of structural analyses allowed determining the morphology of these rods, and selected area electron diffraction experiments pointed out the simultaneous presence of the exotic hexagonal and stable monoclinic phases. Moreover, the presence of potassium inside the nanorods, coming from the mica substrate, was revealed. By combining all the observations, a growth model is proposed, consisting of the stacking of two different crystallographic structures. An interfacial hexagonal KxWO3 tungsten bronze grows in epitaxy on the mica substrate, followed by the growth of monoclinic trioxide tungsten. The stability of these nanometric objects was studied by annealing up to 870 K, indicating that the transformation of the presumed metastable hexagonal phase never occurred.