Effect Of Compositing And Doping On Thermoelectric Properties Of Te,Se-Based Materials

Since more than 40%of the world's produced energy is lost as waste heat in the low temperature ranges,developing high efficient thermoelectrics for energy harvesting from this low-grade waste heat possesses vital significance in the aspects of energy conservation.At present,however,the conversion efficiency?or average ZT?of thermoelectric materials in the low temperature range?<-500K?is too low to satisfy the practical applications in energy harvesting from this low-grade waste heat.Hence,how to raise substantially the conversion efficiency of thermoelectric materials at the low temperatures is a great challenge encountered in the developments of thermolectrics.?1?In summary,by introducing asymmetric interface potentials in PbSe/BST nanocomposites one can concurrently regulate transports of both majority and minority carriers by carrier scattering at the interface potentials.Consequently,enhanced Thermopower from increased EFE and inhibition of minority contributions and large reduction of bipolar effect-related thermal conductivity are realized.Consequently,a maximum ZT=1.56?at 400K?and an average ZT=1.44 in the temperature range from 300K to 500K are achieved for Bi0.4Sb1.6Te3 based composites incorporated with 0.2%PbSe nanoinclusions;correspondingly,a record projected conversion efficiency?10%is reached at 500K.Present result indicates that carrier-scattering engineering strategy is a prospected approach to elevating the performances of thermoelectric materials.?2?The thermoelectric properties of Na-doped polycrystalline NaxSn1-xSe?x=0.001-0.005?,prepared by fusion method,were investigated in the temperature from 300K to 873K.The results show that,upon slightly doping of Na?x<0.005?,besides a large reduction of thermal conductivity the electrical conductivity of Na.Sn1-xSe samples is increased by around two orders of magnitude,reaching 78 Scm-1 at 850K;simultaneously,they possess large values?-300 ?V/K,850K?of thermopower.As a result,a high value of ZT=?1.2?at 873K?is achieved for Na-doped polycrystalline Na_0.003Sn_0.997Se.?3?PbSe/Na_0.003Sn_0.997Se and PbTe/Na_0.003Sn_0.997Se compounds were prepared by using the method consisting of high-temperature melting and hot-pressing under a high pressure.As a result,a high value of ZT=?1.3?at 773K?is achieved for?PbSe?/Na_0.003Sn_0.997Se?f=0.5 vol.%?.