Fabrication of nanotubules of thermoelectric γ-Na0.7CoO2 using porous aluminum oxide membrane as supporting template

We report the successful synthesis of nanotubules of thermoelectric materials γ-NaxCoO2 using two different sol–gel routes aided by porous anodized aluminium oxide (AAO) membrane as supporting templates. The γ-NaxCoO2 nanotubule using urea-based route can be achieved at 650 °C at a heating rate of 1 °C min−1 and held for 4 h. The γ-NaxCoO2 nanotubule using citric acid-based route can be achieved at 500 °C using a rapid-heat-up procedure and held for 30 min. The products were investigated using various techniques including XRD, SEM and TEM. Electron diffraction pattern taken along [0 0 1] zone axis direction on the nanotubule shows that all the diffraction spots can be indexed using a hexagonal unit cell with a = b = 0.56 nm, which can be considered as a superstructure with cell doubling within the ab plane.