Anisotropic Electrical Conductivity of Oxygen-Deficient Tungsten Oxide Films with Epitaxially Stabilized 1D Atomic Defect Tunnels

Materials having an anisotropic crystal structure often exhibit anisotropy in the electrical conductivity. Compared to complex transition-metal oxides (TMOs), simple TMOs rarely show large anisotropic electrical conductivity due to their simple crystal structure. Here, we focus on the anisotropy in the electrical conductivity of a simple TMO, oxygen-deficient tungsten oxide (WOx) with an anisotropic crystal structure. We fabricated several WOx films by the pulsed laser deposition technique on the lattice-matched (110)-oriented LaAlO3 substrate under a controlled oxygen atmosphere. The crystallographic analyses of the WOx films revealed that highly dense atomic defect tunnels were aligned one-dimensionally (1D) along [001] LaAlO3. The electrical conductivity along the 1D atomic defect tunnels was similar to 5 times larger than that across the tunnels. The present approach, introduction of 1D atomic defect tunnels, might be useful to design simple TMOs exhibiting anisotropic electrical conductivity.