Thermoelectric conversion via laser-induced voltage in highly textured polycrystalline NaxCoO2 ceramic

We have studied and analyzed the laser-induced voltage effect in highly c-axis-oriented polycrystalline NaxCoO2. The textured and layered stacking NaxCoO2 (x ∼ 0.7) bulks were prepared by a solid-state reaction process. Under the irradiation on Na0.67CoO2 bulk surface with pulsed laser (λ = 248 nm), the induced voltage signals were observed on the inclined surface with rise time 30 ns-43 ns and peak voltage 200 mV-500 mV; the voltage peak values show a linear dependence of laser energy densities. The crystal grains orientation plays a critical role in voltage peak value whether in film or texture bulk. The transverse voltage signal brings the information of thermoelectric anisotropy. In NaxCoO2 band structure, the Fermi surface is different in the ab plane and along the c axis, leading to anisotropy of Seebeck coefficient. Additionally, the artificial structure of the inclined surface for highly textured bulk enables us to obtain a transverse voltage on inclined surface. These results demonstrated the layered textured bulk has potential applications in waste-heat conversion via transverse thermoelectric effect.