Unraveling the Structure and Properties of Layered and Mixed ReO-WO Thin Films Deposited by Reactive DC Magnetron Sputtering.

Tungsten trioxide (WO) is a well-known electrochromic material with a wide band gap, while rhenium trioxide (ReO) is a "covalent metal" with an electrical conductivity comparable to that of pure metals. Since both WO and ReO oxides have perovskite-type structures, the formation of their solid solutions (ReO-WO or Re W O) can be expected, which may be of significant academic and industrial interest. In this study, layered WO/ReO, ReO/WO, and mixed ReO-WO thin films were produced by reactive DC magnetron sputtering and subsequent annealing in air at 450 °C. The structure and properties of the films were characterized by X-ray diffraction, optical spectroscopy, Hall conductivity measurements, conductive atomic force microscopy, scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoemission spectroscopy. First-principles density functional theory calculations were performed for selected compositions of Re W O solid solutions to model their crystallographic structure and electronic properties. The calculations predict metallic conductivity and tetragonal distortion of solid solutions in agreement with the experimental results. In contrast to previously reported methods, our approach allows us to produce the WO-ReO alloy with a high Re content (>50%) at moderate temperatures and without the use of high pressures.