Coexistence of High Electron Conduction and Low Heat Conduction in Tungsten Oxide Epitaxial Films with 1D Atomic Defect Tunnels

Materials showing unusual electron and heat conduction such as the coexistence of high electron conduction and low heat conduction are essentially important to realize efficient thermal management systems. Although introducing point defects or layers is known as an effective way to reduce the thermal conductivity, the coexistence of high electron conduction and low heat conduction is still challenging because of the fact that electrons and phonons are scattered simultaneously by impurities, defects, and boundaries. Although oxygen-deficient tungsten oxide (WOx) films (2.7 < x < 3.0) show the desired properties, the origin is still unclear. Here, we report that one-dimensional (1D) atomic defect tunnels give rise to the coexistence of low thermal conductivity and high electrical conductivity of WOx films. We fabricated WOx epitaxial films on LaAlO3 substrates under a precisely controlled oxygen atmosphere. Crystallographic analyses revealed that 1D atomic defect tunnels are formed randomly along the rectangular-shaped grains in the in-plane direction. The cross-plane thermal conductivity of the WOx films dramatically decreased with decreasing x, while the electrical conductivity drastically increased because of an increase of carrier electrons, and high electron conduction and low heat conduction coexist when x < 2.9. The present finding would be useful to design efficient thermal management materials.