Anomalous Defect Dependence of Thermal Conductivity in Epitaxial WO3 Thin Films

다국어 초록 (Multilingual Abstract)

Lattice defects typically reduce lattice thermal conductivity, which has been widely exploited in applications such as thermoelectric energy conversion. Here, an anomalous dependence of the lattice thermal conductivity on point defects is demonstrated in epitaxial WO3 thin films. Depending on the substrate, the lattice of epitaxial WO3 expands or contracts as protons are intercalated by electrolyte gating or oxygen vacancies are introduced by adjusting growth conditions. Surprisingly, the observed lattice volume, instead of the defect concentration, plays the dominant role in determining the thermal conductivity. In particular, the thermal conductivity increases significantly with proton intercalation, which is contrary to the expectation that point defects typically lower the lattice thermal conductivity. The thermal conductivity can be dynamically varied by a factor of ≈1.7 via electrolyte gating, and tuned over a larger range, from 7.8 to 1.1 W m−1 K−1, by adjusting the oxygen pressure during film growth. The electrolyte‐gating‐induced changes in thermal conductivity and lattice dimensions are reversible through multiple cycles. These findings not only expand the basic understanding of thermal transport in complex oxides, but also provide a path to dynamically control the thermal conductivity.
An anomalous dependence of thermal conductivity on point defects is observed in epitaxial WO3 thin films. In particular, an increase of the lattice thermal conductivity found in WO3/YAO is accompanied by a lattice contraction upon the introduction of point defects, suggesting that the lattice volume rather than defect concentration plays the dominant role in determining the thermal conductivity.