摘要
Bi 2 Te 3 -based materials are the most commonly used materials in commercial thermoelectric devices. There are many joints in thermoelectric devices, thus knowledge of interfacial reactions with Bi 2 Te 3 substrate is important. Interfacial reactions are examined in the following couples, Sn/Bi 2 Te 3 at 160 °C, In/Bi 2 Te 3 at 140 °C and Cu/Bi 2 Te 3 at 350 °C. The reaction temperatures are all lower than the melting points of the respective reaction substrates, so all these couples are solid/solid couples; however, liquation phenomena are observed in these couples. A reaction zone composed of two regions is formed in the Sn/Bi 2 Te 3 couple reacted at 160 °C. The phase region adjacent to Sn is liquid phase and that adjacent to Bi 2 Te 3 is SnTe with Bi solubility. The liquid phase is of near Bi-Sn eutectic composition and is formed due to alloying between Sn and Bi. The reaction path is Sn/liquid/SnTe/Bi 2 Te 3 . In the In/Bi 2 Te 3 couple reacted at 140 °C, a liquid phase is formed among various reaction phases. The reaction path is In/In 4 Te 3 /liquid/Bi/(Bi 2 ) m (Bi 2 Te 3 ) n /Bi 2 Te 3 . Te atoms diffuse toward In and an In 4 Te 3 phase is formed. Liquid phase is formed due to the alloying between In and remaining Bi. A metastable Cu x Bi 2 Te 3 , an oversaturated Bi 2 Te 3 phase, is formed adjacent to the Bi 2 Te 3 substrate in the Cu/Bi 2 Te 3 couple reacted at 350 °C. The oversaturated phase decomposes, and a stable Cu 2 Te phase is formed. The remaining Bi adjacent to Cu x Bi 2 Te 3 phase is molten at 350 °C, and the remaining Bi in contact with Cu, alloying with Cu and is also molten. Once the liquid phase is formed, the reaction rates become very fast. The reaction paths in the couples are illustrated with the proposed related phase equilibria isothermal sections.