Low thermal conductivity of $CsBiNb2O7$ epitaxial layers

The thermal conductivity of an epitaxial layer of $CsBiNb2O7$ grown by pulsed-laser deposition is measured by time-domain thermoreflectance in the temperature range $100<T<600K$⁠. Characterization by x-ray diffraction and cross-sectional transmission electron microscopy show that the sample has the $n=2$ structure of the Dion–Jacobson series of phases. The conductivity of this layered oxide is $≈60%$ of the predicted minimum thermal conductivity in this temperature range; the thermal conductivity at room temperature, $0.4Wm−1K−1$⁠, is comparable to the lowest conductivity ever observed in an oxide crystal.