Energy-Efficient Synthesis and High Thermoelectric Performance of α-Cu_2-y Se_1-x Te_x

The high-temperature phase of β-Cu₂ Se always appears as the major phase for the reaction carried out using chemical solution methods. Here, a procedure was developed that could fabricate a single phase of α-Cu₂ Se_1-x Te_x (x=0.02 and 0.04) by room-temperature aqueous synthesis using NaBH₄ as reducing agent followed by cold pressing and sintering at 650 °C for 6 h in a flowing gas mixture of 20 % H₂ and 80 % N₂ . The energy-efficient synthesis carried out at room temperature abides by the 6th principle for green chemistry with less energy consumption. The reaction mechanism was studied, and evidence was provided of α-Cu₂ Se being formed via the reaction between elemental Cu and Se atoms at room temperature. The resulting materials were characterized by powder X-ray diffraction, field-emission scanning electron microscopy, thermoelectric transport measurements, and Hall measurements. Cu_1.96 Se_0.96 Te_0.04 had the highest power factor of 11 μW cm^-1 K^-2 at 818 K, and Cu₂ Se_0.96 Te_0.04 had the maximum zT≥1.4 at T≥920 K among this series of materials.