Study On The Performance Of Bi And Cu Sites Dual Doped Layered BiCuSeO Based Thermoelectric Materials

Thermoelectric materials are widely concerned because of the ablity of direct conversion between heat and electric energy.BiCuSeO is a new type of oxide thermoelectric material,and has become a research hotspot in recent years due to high temperature resistance,good chemical stability,low cost and non-pollution.However,it is still difficult for large-scale applications due to moderate thermoelectric performance.The purpose of this paper is to optimize the thermoelectric properties of BiCuSeO by dual doping at Bi and Cu sites.The results of the study are as follows:(1)Ba and Co dual doped BiCuSeO was prepared by solid state reaction and their thermoelectric properties at low temperature were studied.Compared with undoped BiCuSeO,the electrical conductivity of the doped samples was greatly improved,which can be attributed to the increase of carrier concentration.Although the carrier concentration of Ba and Co dual doped samples decreases to a certain extent compared with that of Ba single doped samples,the carrier mobility is improved and the electrical conductivity is still high.In addition,Ba and Co dual doped samples retain a higher Seebeck coefficient than Ba single doped sample due to the improvement in effective mass of this material.The figure of merit of Ba and Co dual doped samples has greatly improved compared with the Ba single doped sample and undoped BiCuSeO,maximum figure of merit of 0.082 is obtained for Ba0.125Bi0.875Cu0.85Co0.15SeO at 350 K,which is 5 times as much as that of Ba single doped sample.(2)Ba and Ni dual doped BiCuSeO were prepared by solid state reaction method,and their thermoelectric properties at medium and high temperature were investigated.Compared to undoped BiCuSeO,the electrical conductivity of doped samples has been greatly increased because of the sharp increase of carriers.Due to the contribution of spin entropy caused by magnetic Ni,the Ba and Ni dual doped samples maintained a higher Seebeck coefficient while having a larger carrier concentration,which lead to a higher power factor.Moreover,because of the diatomic point defects introduced by dual doping,the phonon scattering of this dual doped material were enhanced,as a result,the thermal conductivity of the dual doped sample is reduced to 0.54 W m-1 K-1.By synergistically optimizing electronic and phonon transport,the thermoelectric properties of BiCuSeO were remarkably enehanced,for example,the figure of merit of Bi0.875Ba0.125Cu0.85Ni0.15SeO reached 0.97 at 923 K.(3)Ba and Ni dual doped BiCuSeO were prepared by different process methods,and the influence of preparation process to the thermoelectric properties of this material were studied.The Seebeck coefficient of smples prepared by manual grinding is low,but their electrical conductivity is far higher than the samples prepared by ball milling.Due to high conductivity,the samples prepared by manual grinding have high power factors near room temperature,power factor of Ba0.875Ba0.125CuSeO at 300 K is 6?W cm-1 K 2.The power factor of Ba and Ni dual doped BiCuSeO prepared by ball milling increases with the increase of temperature,and has the highest power factor at high temperature,power factor of 5.7 ?W cm-1 K-2 is obtained for Bi0.875Ba0.125Cu0.85Ni0.15SeO at 923 K.