Preparation And Thermoelectric Properties Of P-type Bi-Te Based Alloys

With the continuous development of human society,the contradiction between the demand for energy and green development has become increasingly fierce.In recent years,the scientific community has paid attention to the research on new energy conversion materials such as thermoelectric materials.At present,the more mature thermoelectric materials are Bi-Te based binary and ternary alloys,which are mainly used in industrial refrigeration applications.However,the actual industrial demand is thermoelectric power generation.Nearly 60%of the global energy resources are supplied by fossil fuels 40%of the heat generated by the combustion is converted,and the remaining energy cannot be effectively collected and utilized.If a new technology and product is developed,this part of energy can be efficiently collected and utilized,which may make a significant contribution to the growing energy crisis and environmental protection.In this paper,p-type Bi_0.5Sb_1.5Te₃?BST?is selected as the matrix.BST was annealed at different temperature,coated with Ag and prepared by different methods.The influence of thermoelectric properties and mechanical properties of materials were studied,specific as follows:?1?The thermal stability of p-type Bi_0.5Sb_1.5Te₃ was simulated by prolonged annealing.The results show that the annealing process is accompanied by the interaction between the antisite-defects and its interactions,the maximum thermal stability temperature can reach 473K,the thermoelectric figure of merit of the sample annealed at low temperature increases up to 1.05,an increase of 8%and annealing at 523K,the performance deterioration significantly;?2?The effects of electroless plating Ag on the thermoelectric properties of p-type Bi_0.5Sb_1.5Te₃ were explored.The results show that the chemical deposition of Ag on the surface of BST can diffuse into the matrix during the sintering process to replace the Bi and Sb atoms and generate the second phase of Ag₂Te.The results are:?1?Defects such as2)^?₄??7??and2)^??₄??7??cause a large increase in electrical conductivity.The greatly increased carrier concentration effectively suppresses bipolar excitation;?2?Phonon scattering is strengthened,the lattice thermal conductivity is reduced.?3?The maximum zT=1.0 and 0.969 of the electroless silver samples did not significantly improve compared with the zT=0.97 of the original BST sample,while the average zT?0.9 and0.88?of the samples in the range of 300 to 423K were significantly 41%higher than that of BST?0.64?;?,for evaluating the energy conversion efficiency of thermoelectric devices,the maximum value reached 9.68%,34.6%higher than that of the BST sample.?3?The effects of different preparation processes on the thermoelectric properties of Ag/Bi_0.5Sb_1.5Te₃ were explored.The results show that the Ag/BST samples prepared by simple mechanical mixing have the same thermoelectric properties as the BST;the preparation of Ag/BST by electroless plating and mechanical alloying can effectively shift the optimum temperature range of thermoelectric properties of BST?form 323K to400K and 423K?;the average thermoelectric figures of merit are higher than the original value.