Na-doping effects on thermoelectric properties of Cu_2-xSe nanoplates

For this work, a β-phase Cu_2-xSe nanowire and nanoplate, and a Na-doped Cu_2-xSe nanoplate were successfully synthesized using solution syntheses. The morphologies of the Cu_2-xSe nanowire and nanoplate could be easily controlled by changing the synthetic condition. The Na-doped Cu_2-xSe nanoplate was prepared by a simple treatment of the Cu_2-xSe nanoplate with a sodium hydroxide-ethylene glycol solution. The nanopowders were then consolidated to bulk materials using spark plasma sintering (SPS). The phase structure and the microstructure of all of the samples were checked using X-ray diffraction (XRD), high-resolution transmission electron microscope (HR-TEM), and scanning electron microscope (SEM) analyses. The thermoelectric transport properties, such as the electrical conductivity, Seebeck coefficient, carrier concentration, carrier mobility, and thermal conductivity, were measured at temperature ranges from 323 to 673 K. The results show that Na played two important roles: one is reducing the carrier concentration, thereby improving the Seebeck coefficient, the other is reducing the thermal conductivity. Overall, the maximum thermoelectric figure of merit (ZT) of 0.24 was achieved at 673 K in the Na-doped Cu_2-xSe nanoplate.