Structure Transformation And Thermoelectric Performance Based On Defect Engineering In Ca_1-x-?Sr_?La_xAg_1-ySb?0???0.7?

With the development of the industrialization,the traditional fossil energy will be difficult to meet the needs of human production and living,at the same time,large amounts of energy in the form of heat overflow due to the low energy conversion efficiency,then produced more environmental problems.In this situation,thermoelectric materials,as a kind of functional semiconductor which can realize the convert from heat to electricity,have attracted more and more attention in recent years.The thermoelectric materials involve a lot of material systems,so cover a wider temperature range of application,which can realize low temperature refrigeration,power generation of waste heat in life and industrial,as well as deep space detection.In conclusion,the TE materials are helpful for realizing more efficient use of limited resources.Zintl phase Ca1-xRExAg1-ySb(RE = La,Ce,Pr,Nd,Sm;0?x?1;0?y?1)has been proved to exhibited potential thermoelectric performance,due to the transformation from TiNiSi-type to LiGaGe-type with Ag-defects introduced.Further,the crystal structure can be adjusted by more Ag-defects introduced by controlling RE content.This flexible defect structure provides more possibility in boosting thermoelectric performance.However,the exploration of these structural transformation is not complete,and the relevant results and mechanisms are not clear.In this work,we continue to boost the TE performance of Zintl phase compound Ca1-xRExAg1-ySb(0?x?1;0?y?1)and the "1-1-1" materials system has been discussed in depth,summarized as follows.1.The Ag-defects have been proved to have important influence on the electronic band structure and transport performance of the material,which is decisive for controlling thermoelectric properties.We further controlled the Ag-defects in the Zintl phase Ca0.85La0.15Ag1-ySb,designed and synthetic materials Ca0.85La0.15Ag1-ySb(0.11?y?0.13)through a home-made micro induction furnace.We obtained the optimal Ag-defects concentration at about 0.11,and the zT value was about 0.52 at 860 K.2.A series of materials Ca0.85-?Sr?La0.15Ag1-ySb(0.1???0.7)have been designed to explore more structural mechanism related based on the defect engineering and control the defects.The complete coplanar[AgSb]layers occurred during a continuous structural transformation from LiGaGe-type to ZrBeSi-type,which further impacts the carrier concentration significantly and enhance the thermoelectric performance.For material Ca0.55Sr0.3La0.15Ag0.89Sb,a maximum zT of 0.7 obtained at 823 K and the average figure of merit is about 0.66 over a temperature range from 774 to 1068 K,which processes a good application prospect.3.Further extended the "1-1-1" materials system,we obtained a series of Mg-/Na-doped SrAgSb materials with different contents and explored the thermoelectric performance preliminarily.