Synthesis And Thermoelectric Properties Of Type Ⅰ Ge Clathrates A₈～ⅡB₁₆～ⅢB₃₀～Ⅳ

Type I clathrates have cage-like structure which leads to their good electrical properties. Meanwhile, their thermal conductivity can be markedly reduced via filling alkaline earth or lanthanon into their cages. Therefore, they are promising thermoelectric materials. It is suggested both the filling atoms and the framework atoms must be optimized in order to further improve the thermoelectric properties.We had researched preparation method of single-phase type I Ge-based clathrates in this paper. The influences of Sb&Zn-doping and Ba/Ce dual atoms filling on the structure and thermoelectric properties of Ba₈Ga₁₆Ge₃₀ compound were investigated systematically. Meanwhile, we investigated the influences of the preparation craft on the thermoelectric properties of Ba₈Zn₈Ge₃₈ compound. Research results indicate that:In n-type Ba₈Ga_16-xSb_xGe₃₀ compounds, with the increase of Sb substitution fraction x, Seebeck coefficient is decreased gradually. The temperature, which corresponded with the peak values of Seebeck coefficient, moves to low-temperature. The electrical conductivity of compounds increases at first and then decreases with the increase of x;when x=2, it reaches the maximum. The substituting Sb for Ga has a great influence on the thermal properties of the compounds. Their thermal conductivity and lattice thermal conductivity all have a decrease in various degree. In all n-type Ba₈Ga_16-xSb_xGe₃₀ compounds, Ba₈Ga₁₄Sb₂Ge₃₀ compound has the greatest ZT value, and its maximal ZT value reaches 1.1 at about 950K.Ce-doping has not influenced the electrical conductivity of n-type Ba_8-xCe_xGa₁₆Ge₃₀ compounds notably. Seebeck coefficient increases gradually with the increase of Ce filling fraction x, but the increasing range is not very large. Their thermal conductivity and lattice thermal conductivity all have a decrease in various degree. In all n-type Ba_8-xCe_xGa₁6Ge₃₀ compounds, Ba₆Ce₂Ga₁₆Ge₃₀ compound has the greatest ZT value, and its maximal ZT value reaches 0.7 at about 1000K.The electrical conductivity of n-type Ba₈Ga_16-2xZn_xGe_30+x compounds increases gradually with the increase of Zn substitution fraction x. The Seebeck coefficient is decreased gradually with the increase of x. When Zn replace Ga entirely, the electrical conductivity of Ba₈Zn₈Ge₃₈ compound drops rapidly and its Seebeck coefficient increases suddenly. Their thermal conductivity and lattice thermal conductivity have a similar alteration law. When x<4, with the increase of x, lattice thermal conductivity is decreased gradually. When x>4, with the increase of x, lattice thermal conductivity increases gradually. In all n-type Ba₈Ga_16-2xZn_xGe_30+x compounds, Ba₈Ga₈Za₄Ge₃₄ compound has the greatest ZT value, and its maximal ZT value reaches 0.85 at about 1000K. The electrical conductivity of the compound, which was prepared by fusion-slow-cooling craft, is far greater than the compound, which was prepared by SPS. But its relatively low Seebeck coefficient leads to a low Power factor, which is slightly smaller than the compound prepared by SPS in the high-temperature part.