Structure And Thermoelectric Properties Of P-Type Cu-Ga-Te Based Defect Compounds

and Cu2Ga4Te7are all the typical semiconductors with sphalerite structure, and their bandgap are Eg=1.0eV(CuGa3Te5) and Eg=0.87eV (Cu2GauTe7) respectively. There is an inherent Coulomb attraction between charged Ga+2cu and2V-1cu in these semiconductors (a native defect pair, i.e., metal Ga-on-Cu antisites and two Cu vacancies). This defect pair is critical to the modulation of the band structure and thermoelectric performance.In this work, we prepared these materials using powder metallurgy and spark plasma sintering (SPS) technology, investigated the structures and thermoelectric properties by using the non-isoelectronic substitutions of elements in Cu-Ga-Te, The detailed achievements have been summarized below.1. The ternary single phase semiconductors CuGa3Te5was prepared with direct band gap of Eg=1.0eV. The highest thermoelectric figure of merit ZT of CuGa3Te5is0.3at717K.2. The compounds Cu1-xGa3SbxTe5(x=0,0.02,0.1,0.2) through substitution of element of Sb for Cu in CuGa3Te5have relatively low thermal conductivity, and the highest dimensionless figure of merit is0.42for Cu0.98Ga3Sb0.02Te5at 701K, which increases about40%compared with that of intrinsic CuGa3Te5.3. Upon the substitution of Sb for Cu, We have prepared quaternary compound Cu2-xGa4SbxTe7(x=0,0.05,0.1,0.2) and have attained the highest dimensionless figure of merit of0.41for Cu1.95Ga4Sb0.05Te7at719K, which increases about14%compared with that of intrinsic Cu2Ga4Te7.4. We observed that the Seebeck coefficients of the compounds Cu2-xGa4ZnxTe7(x=0,0.05,0.1,0.2) and Cu2Ga4-xZnxTe7(x=0,0.05,0.1,0.2) increase with the Zn content increasing due to the increase in the local density of states(DOS) at the Fermi level and the effective mass of the valence band. However, the electrical conductivities decrease mainly because of the widening of the bandgap (Eg). The gradual enhancement in the lattice thermal conductivity with the Zn content is due to the reduction of phonon scattering caused by the decrease of the vacancy concentration. Therefore, we have attained the maximum ZT value of0.47at770K when a proper Ga or Cu is substituted for Zn, which is about22%higher than that of intrinsic Cu2Ga4Te7.