Preparation And Properties Of P-type Tin Selenide Based Thermoelectric Materials By Cold Sintering

In recent years,due to the increasingly serious environmental pollution and energy crisis,many foreign and local scholars pay more and more attention to the study of renewable energy.Thermoelectric materials have attracted wide attention because of their ability to realize the direct conversion of electricity and heat.However,the low conversion efficiency of thermoelectric devices limits their practical applications.In order to improve their conversion efficiency,most of the research work focuses on improving the thermoelectric figure of merit（ZT）of thermoelectric materials.At present,spark plasma sintering（SPS）technology is mainly used for the preparation of thermoelectric materials.However,due to the disadvantages of high energy consumption and expensive equipment,thermoelectric materials researchers urgently need a kind of sintering technology with mild processing conditions,energy saving and economic efficiency.As a new sintering technology developed in recent years,cold sintering technology can effectively reduce the sintering temperature of materials by introducing liquid phase sintering,and the preparation process is simple and the equipment requirements are low.It is hoped to provide a new,more energy-saving and more environmentally friendly method for the preparation of thermoelectric materials.This topic is mainly focused on p-type SnSe-based thermoelectric materials as the main research object,which committed to using cold sintering technology to reduce sintering temperature while maintaining excellent thermoelectric properties of materials.The effects of different cold sintering parameters on the density,microstructure and thermoelectric properties of the samples were mainly discussed,and the thermoelectric properties of the materials were further improved by using composite materials and doping.The main research contents and conclusions are as follows:（1）The influence of different temperature,holding time and pressure on the density,microstructure and thermoelectric properties of SnSe block materials during cold sintering was explored.The experimental results show that the minimum densification temperature of SnSe is260℃,and the increase of cold sintering temperature can effectively reduce the thermal conductivity of the material.Different holding time and pressure will affect the microstructure and thermoelectric properties of materials.Among the process parameters selected in this experiment,the best cold sintering process parameter is 300℃,154 MPa holding for 30 min.（2）The influence of cold sintering liquid phase type on the density and thermoelectric properties of SnSe bulk materials was explored.The experimental results showed that for SnSe materials,the performance of the sample prepared by adding 10 wt%H₂O as cold sintering liquid phase was significantly higher than that of other samples,and the maximum ZT value was about1.3 at 900 K.Compared with cold sintered samples without sintering additives and samples prepared by SPS technology,the maximum ZT value increased by 44%and 76%,respectively.The SnSe bulk material prepared by cold sintering with 10 wt%H₂O was annealed to study its thermal stability.The experimental results show that the density and carrier concentration of the sample increase further after annealing,which significantly improves the ZT value of the sample at low temperature.（3）As the conductivity of SnSe thermoelectric materials prepared by cold sintering is low,the conductivity of SnSe materials is improved by the composite of two-dimensional material MXene,thus improving the thermoelectric properties of the materials.The effects of different contents of MXene on the density,phase composition,morphology and thermoelectric properties of SnSe bulk materials were studied.The experimental results show that the composite MXene improves the electrical conductivity of SnSe material,but also reduces the Seebeck coefficient and increases the thermal conductivity.The ZT value of the composite 1.5 vol%MXene sample is the highest,which is about 1.0 at 900 K.（4）The effects of different Ag doping quantities on density,phase composition,microstructure and thermoelectric properties of Ag_xSn_1-xSe bulk materials were investigated.The experimental results show that Ag doping can significantly improve the conductivity of Ag_xSn_1-xSe materials and Ag₈SnSe₆ precipitation occurs during the sintering process,thereby reducing the lattice thermal conductivity of samples at high temperature.When x=0.0075,the ZT value of Ag_xSn_1-xSe bulk material is the highest,about 1.6 at 900 K,which is about 23%higher than that of undoped Ag samples.