Growth And Transport Properties Of Two Transition Metal Thermoelectric Compounds

Since the Industrial Revolution of the 19th century,the demand for energy has grown rapidly all over the world.In order to meet the energy demand of industrial production and daily life,non-renewable energy(such as coal,oil,natural gas and other fossil fuels)has been extensively exploited and used,resulting in serious environmental pollution problems,such as air pollution,greenhouse effect,acid rain and so on.Compared with other countries,energy situation of China is not optimistic,because of the large demand for energy and the the inefficient use of energy.China has been the second largest energy producer and consumer in the world since 2007.Carbon dioxide emissions are the second largest in the world.Due to the non-optimized energy usage structure and the energy use inefficiency,China has caused serious energy waste,which has caused serious pollution and environmental problems.In China,about 60%of industrial energy is converted into industrial waste heat,and the utilization rate of industrial waste heat is as low as 30%.Therefore,in order to reduce energy waste and environmental pollution,it is urgent for China to increase the utilization rate of industrial waste heat.In this background,thermoelectric materials have come into people’s vision and attracted intensive attention,because the thermoelectric effect enables the direct conversion of heat to electrical energy,and can be used to take advantage of industrial waste heat.Thermoelectric material is an environment-friendly heat-electrical-energy conversion material,which has the advantages of small size,high reliability,pollution-free,wide temperature application range and so on.At present,the efficiency of thermoelectric devices are still not high enough,so it is necessary to study the electrical and thermal transport properties of thermoelectric materials to improve their thermoelectric performance,promote the practical utilization of thermoelectric materials in industrial production and daily life to achieve the ultimate goal of improving the utilization rate of waste heat,conserving energyand protecting the environment.In this paper,a series of single crystal and polycrystalline ceramics samples of thermoelectric materials have been prepared by different methods.The electrical and thermal transport properties of these materials have been measured by Physical Property Measurement System.The main conclusions are:1.Te-deficient ZrTes-s single crystal and Te-rich ZrTes+s polycrystalline ceramics were grown by chemical vapor transport method and high temperature solid-state reaction method respectively.The electrical and thermal properties of Te-deficient ZrTes-δ single crystal and Te-rich ZrTes+s polycrystalline ceramics were studied and compared by Physical Property Measurement System characterizations.It is found that the electrical transport properties of ZrTes compounds are changed by controlling the stoichiometry of Te elements so that the thermoelectric parameters of ZrTe5 compounds can be adjusted and the thermoelectric properties of ZrTes compounds can be improved.In details,the electrical resistivity,Seebeck coefficient,thermo-conductivity and ZT value of ZrTe5+δ ceramics are 6.0 mΩ ·cm、123μV K-1、1.86W/(m·K)and 0.037 measured at 300K，respectively.ZT value of our sample is higher than those of ZrTes/HfTes at previous reports.Our work provides an idea for further improving the thermoelectric properties.2.BiCuSO single crystal,BiCuSeO single crystal and BiCuTeO polycrystalline ceramics were prepared by chemical vapor transport method and high temperature solid-state reaction method respectively.The electrical transport properties of BiCuSO single crystal,BiCuSeO single crystal and BiCuTeO polycrystalline ceramics were studied and compared by Physical Property Measurement System characterizations.The electronic scattering mechanism of BiCuXO(X=S,Se,Te)materials was systematically studied.We found that element replacement from S to Te dramatically decreases the electrical resistivity of BiCuXO compounds.Moreover,the carrier scattering by electron-phonon interaction is decreased when the compound changes from BiCuSO to BiCuTeO.Summarizing the experimental results and theoretical analysis of ZrTes and BiCuXO(X=S,Se,Te)compounds,we find that the control of element stoichiometry and element substitution can effectively control the electrical transport properties of materials.Therefore,based on the methods above,we can modify the electrical conductivity of thermoelectric materials,improve their thermoelectric properties.The study of electrical scattering mechanism may provide new ideal on how to improve electrical property of thermoelectric materials.