Strontium-deficient Sr$_x$CoO$_2$–CoO$_2$ nanotubes as a high ampacity and high conductivity material

Continuous miniaturization of electronics demands the development of interconnectors with high ampacity and high conductivity, which conventional conductors such as copper and gold cannot offer. Here we report the synthesis of Sr-deficient misfit Sr$_x$CoO$_2$–CoO$_2$ nanotubes by a novel crystal conversion method and investigate their electrical properties. Bulk Sr$_6$Co$_5$O$_{15}$ having a quasi-one-dimensional CoO$_6$ polyhedral structure (face-sharing octahedron and trigonal prismatic CoO$_6$ arranged in one-dimension) is converted to Sr$_x$CoO$_2$–CoO$_2$ nanotubes where CoO2 adopts a two-dimensional edge-sharing CoO$_2$ layered structure in a basic hydrothermal process. Electrical properties measured on individual nanotubes demonstrate that these nanotubes are semiconducting with a conductivity of 1.28 × 10$^4$ S cm$^{−1}$ and an ampacity of 10$^9$ A cm$^{−2}$, which is the highest reported ampacity value to date of any inorganic oxide-based material. The nanotubes also show a breakdown power per unit channel length (P/L) of ∼38.3 W cm$^{−1}$, the highest among the regularly used interconnect materials. The above results demonstrate that Sr$_x$CoO$_2$–CoO$_2$ nanotubes are potential building blocks for high-power electronic applications.