Structure And Thermoelectric Properties Of P-Type Cu₃Ga₅Te₉Semiconductors

Cu3Ga5Te9is one of the typical Ⅰ-Ⅲ-Ⅵ2series semiconductor with chalcopyrite structure. In these semiconductors there is an inherent Coulomb attraction between charged GaCu2+and2Vcu (a native defect pair, i.e., metal Ga-on-Cu antisites and two Cu vacancies) which has a profound effect on the electronic and structural properties. Although the concentration of the donor or acceptor defect can be high, they are easily annihilated under the inherent Coulomb attraction. However, Cu3Ga5Te9semiconductor has a relatively ideal carrier concentration n (～1025m-3), it therefore has a potential to improve the thermoelectric performance. In this light, we have investigated the structures and thermoelectric properties with the non-isoelectronic substitutions of elements in Cu3Ga5Te9, and made some achievements which are summarized below in detail.1. We have employed non-isoelectronic substitution of Sb for Cu and Te in Cu3Ga5Te9, and observed an increase the Seebeck coefficient and electrical conductivity. This improvement is attributed to the enhancement in carrier concentration n and effective mass as well as the conservation of the carrier mobility μ. The enhancement of the carrier concentration is caused by the hole doping effect due to the drop of the Fermi level into the valence band when Sb occupies the Te lattice sites, and also to the increase of the copper vacancy (V-’cu) concentration when Cu content decreases. In addition, the non-isoelectronic substitution yields extra crystal structure defects. These defects, which are represented by the alterations of anion (Te2-) position displacement (u) and tetragonal deformation (η), directly govern the lattice thermal conductivity (κL) on an atomic scale. The maximum ZT value is0.6at766K with proper Sb substitution, which is about25%higher than that of Cu3Ga5Te9.2. We have prepared quaternary compound Cu3-xGa5MnxTe9(x=0.05,0.1,0.2) through substitution of element of Mn for Cu in Cu3Ga5Te9. Upon substitution, the Seebeck coefficients (a) remain almost unchanged, and the electrical conductivities increase a lot along with the significant reduction in thermal conductivity. The highest ZT value is0.79, which increases by65%compared to that of intrinsic Cu3Ga5Te9. Upon substitution of Mn for Ga in Cu3Ga5Te9, the Seebeck coefficients (a) are almost unchanged but the electrical conductivities increase by44%along with the reduction in thermal conductivities. On the other hand, the co-substitutions of Mn for Cu and Ga in Cu3Ga5Te9alter the binding energies of the Cu-Te or Ga-Te and confirm that the element Mn is incorporated into the lattice of the compound Cu3Ga5Te9, which yields a ZT value of0.59at737K.