Structure And Thermoelectric Properties Of Ag-containing Ternary Chalcogenides

Ever-growing energy consumption and increasingly severe environmental issues have drawn extensive attention in recent years.Thermoelectric materials,based on the direct energy conversion between heat and electricity,have been considered as a promising alternative solution to the challenges of the global energy dilemma.AgBiSe₂belongs to a Ag-containing ternary n-type?-?-?₂chalcogenides.Due to the low-cost of the elements,this compound has attracted much attention in thermoelectrics.In this work,AgBiSe₂is selected as the target material,based on which the relationships between the thermoelectric properties and the structure have been investigated.The main results are summarized below.(1)A series of materials(Ag_1-yIn_yBiSe_2-zS_z)_1-x(Ag₂Se)_xwere synthesized by sequential doping to engineer the chemical compositions.This engineering is realized by doping Ag₂Se at first and then In and S in succession,which leads to the creation of impurity levels within the gap.The reduction in?_Lis ascribed to the mass/size mismatch and/or structure anharmonicity.As a result,the material(Ag_0.995In_0.005BiSe_1.99S_0.01)_0.95(Ag₂Se)_0.05gives the highest ZT value of?0.94 at 770 K.(2)Upon addition of Ag₂Te in AgBiSe₂,Ag₂Te has successfully incorporated into the crystal lattice,which allows the dilation of the lattice structure.As a result,we attain the highest ZT value(?1.0)for the sample(AgBiSe₂)_0.925(Ag₂Te)_0.075at 770 K,which is 1.82 times that of the pristine material.This result reveals that an appropriate doping of Ag₂Te in AgBiSe₂can effectively improve the thermoelectric performance.(3)Upon Cu addition in AgBiSe₂,we attain the solid solutions Ag Cu_xBiSe₂.XRD analysis reveals that the peaks shift toward high diffraction angles with Cu content increasing,indicating that the lattice structure suffers contraction.At 770 K,the power factor of Ag Cu_0.075BiSe₂increases from 2.8?W cm^-1K^-2to 3.92?W cm^-1K^-2,but the thermal conductivity is almost comparable to that of the pristine AgBiSe₂.Eventually,the TE performance improves with the highest ZT value of?0.64,increasing by?16%compared to that of the pristine AgBiSe₂.