Adjustment Of Electrical And Thermal Transport Properties In Antimony-based Cage-like Thermoelectric Compounds

Thermoelectric?TE?material is a type of functional materials,which can interconvert waste heat into useful electricity directly by the movement of carriers.TE devices?included thermal gradient-power-generation devices and TE cooling devices?constructed by TE materials have many advantages,such as working safely and reliably,emission without polluted matters and noise,no-moving-parts,and easier to maintain,which attract much scientific interest.Due to rich structural features?layered and cage-like substructure?and promising thermoelectric performances,antimony-based Zintl compounds AM₂Sb₂?A=alkaline earth elements or divalent rare earth elements,M=transition elements?have attracted much attention for fundamental researches in recent years.BaZn₂Sb₂?orthorhombic,space group Pnma?which consists of network of Zn-Sb and Ba ions,is a typical Phonon Glass-Electric Crystal?PGEC?model.Earlier investigations reveal that this compound exhibit considerable electrical and thermal transport properties and is one of promising middle-temperature TE materials.In this paper,BaZn₂Sb₂ compounds(Ba_1-xNa_x Zn₂Sb₂?0?x?0.1?,Ba_1-ySr_yZn₂Sb₂?0?y?0.1?,Ba_0.94-xNa_0.06Sr_xZn₂Sb₂?0?x?0.1?,Ba(Zn_1-xAg_x)₂Sb₂?0?x?0.01?and Ba(Zn_1-yCu_y)₂Sb₂?0?y?0.01?)were successfully prepared by solid state reaction method and hot-pressing sintering.The crystal structure and corresponding thermoelectric parameters were characterized in order to understand the structure-properties relationship.Simultaneously,the effects of substitution at different sites in Ba Zn₂Sb₂ on the TE properties were investigated systematically.The main results are as followed:1.Dopant Na was rationally introduced in BaZn₂Sb₂ with the aim to tune carrier concentration.The electric and thermal transport properties of Ba_1-xNa_x Zn₂Sb₂?x=0,0.03,0.06,0.08,0.09,0.10?at the temperature range of300⁷23 K show that when x?0.06,the electric conductivity increases with the increasing Na content while the variation tendency of Seebeck coefficient is opposite to the electrical conductivity.The power factor is 10.46?Wcm^-1K^-2 for Ba_0.94Na_0.06Zn₂Sb₂ at 697 K,which is almost twice as large as the highest value of undoped BaZn₂Sb₂ sample(5.39?Wcm^-1K^-2,464 K).The thermal conductivity increases gradually with Na amounts increasing?x?0.06?and varies from 1.27Wm^-1K^-1 to 2.71 Wm^-1K^-1 at the room temperature.Finally,the ZT value for Ba_0.94Na_0.06Zn₂Sb₂ sample reaches to 0.53 at 697 K.2.Dopant Na was rationally introduced in BaZn₂Sb₂ with the aim to tune the lattice thermal conductivity.The cell parameter a,b,c for Ba_1-ySr_yZn₂Sb₂?y=0,0.02,0.04,0.06,0.08,0.10?decrease with y increasing.The electric and thermal transport properties at the temperature of 300 K⁷23 K show that the electric conductivity firstly increases?0?y?0.04?and then decreases?y>0.04?with increasing Sr contents.The variation of seebeck coefficient with Sr amounts is opposite to the electrical conductivity-firstly decreases and then increases.The power factor slightly increases.After doping Sr,the lattice thermal conductivity of Ba Zn₂Sb₂-based samples decreases obviously.At 696 K,the ZT value of the Ba_0.98Sr_0.02Zn₂Sb₂ sample is 0.45.3.Due to the distinguishing fuction of Na and Sr on BaZn₂Sb₂,the electric and thermal transport properties of Na/Sr codoped Ba_0.94-yNa_0.06Sr_yZn₂Sb₂?y=0,0.02,0.04,0.06?samples are investigated.The results show that the power factor of Ba_0.92Na_0.06Sr_0.02Zn₂Sb₂ sample reaches to 12.46?Wcm^-1K^-2 at 704 K and the thermal conductivity also decrease at the room temperature.Finally,the ZT value is the highest for Ba_0.92Na_0.06Sr_0.02Zn₂Sb₂ sample,reached to 0.58,which is greater than that for undoped Ba Zn₂Sb₂ sample at the same temperature by 66%.4.The doped effects in Zn site are investigated.respectively,The electric and thermal properties of Ba(Zn_1-x Ag_x)₂Sb₂?x=0,0.002,0.004,0.006,0.008,0.01?and Ba(Zn_1-xCu_x)₂Sb₂?x=0,0.002,0.004,0.006,0.008,0.01?at the temperature range of300 K⁷73 K show that the electric conductivity of Ba(Zn_1-xAg_x)₂Sb₂ samples increase constantly with the Ag fraction increasing,Seebeck coefficient decrease constantly and the thermal conductivity increase constantly.The ZT value of Ba(Zn_0.996Ag_0.004)₂Sb₂ sample is 0.63 at 760 K.The variation tendency of the electric and thermal transport properties for Ba(Zn_1-yCu_y)₂Sb₂ samples is similar to Ba(Zn_1-xAg_x)₂Sb₂ samples,but the efficiency is slightly poor.The ZT value of Ba(Zn_0.996Cu_0.004)₂Sb₂ sample reaches to 0.53 at 762 K.5.The electric and thermal properties at the temperature range of 300 K⁷73K for p-type BaCu₂Te₂ TE materials show that BaCu₂Te₂ TE materials possess better electric properties,because the order of magnitude of electric conductivity is at 10⁴.And the thermal conductivity also is lower.Thus,the ZT value reaches to 0.77 at 762K,which demonstrates BaCu₂Te₂ is a new Zintl phase cage-like TE material having superior TE materials.