Study On The Structural Modification And Thermoelectric Transport Properties Of The BiCuSeO Thermoelectric Materials

With the continuous progress and development of social industrialization,the oil,coal and other energy sources are gradually depleted,while the utilization of traditional energy sources has also caused a sharp deterioration of the environment.The synergic relationship of the energy and the environment has became a critical factor for the future social and economic development.In recent years,the high-efficiency and multi-level utilization of renewable energy has been highly valued all over the world as an important way to solve energy shortages and environmental pollution.The widespread utilization of renewable energy,such as wind and solar energy,has reduced the consumption of traditional energy sources to a certain extent.In addition,in terms of efficient use of energy,thermoelectric materials,as a new type of energy conversion materials that can realize the direct conversion between heat and electric energy.Moreover,the energy conversion in thermoelectric materials is out of the mechanical movement and chemical transmission media compared with traditional energy utilization methods.Thermoelectric conversion technology is therefore considered to be a clean and pollution-free energy conversion technology.Based on the unique advantages of thermoelectric technology,thermoelectric materials have been widely used in the waste heat recovery of automobile exhaust,spacecraft power supply,industrial heat recovery,thermoelectric refrigeration,etc.With the huge market demand and the efforts of scientific researchers,thermoelectric materials are expected to become an important approach to solve energy shortages with their unique advantages.The development of thermoelectric materials originated from the discovery of the Seebeck effect.With the continuous development of the solid-state physics,semiconductor basic theories,and the unremitting efforts of scientific researchers,the theories of thermoelectric transport performance have been improved gradually,resulting in thatthe thermoelectric conversion efficiency is improved continuously.At present,there are many types of thermoelectric materials.Oxygen-containing compounds were received long-term attention from scientific researchers in the development of thermoelectricity.As a new member of thermoelectric materials,BiCuSeO as oxygen-containing compounds have the stable high-temperature performance,oxidation resistance,non-toxic,easy sintering,etc,and due to its low intrinsic thermal conductivity,BiCuSeO are considered as potential high-performance thermoelectric materials.A large number of experiments and theoretical studies have shown that in-situ high pressure can manipulate the lattice structure,electron transport,energy band structure,and microscopic morphology in thermoelectric materials,and directly or indirectly modulate thermoelectric transport parameters.Therefore,high pressure is considered as a new research strategy for the manipulation of thermoelectric performance.In this paper,we successfully prepared BiCuSeO bulk thermoelectric materials using the typical representative of high-pressure technology"high-temperature and high-pressure method",and systematically preformed the high-pressure synthesis of BiCuSeO materials and of the study on the effect of Te doping on the thermoelectric transport performance of BiCuSeO materials under high pressure.The main research contents are shown as follows:(1)The BiCuSeO material was prepared by high temperature and high pressure method under different pressures.The results showed that the crystal structure and microstructure of BiCuSeO gradually changed with the increase of synthesis pressure(0.8-4 GPa).Due to the application of high pressure,the band structure and electronic structure of the material are optimized.As the synthesis pressure increases,the band gap of the prepared sample graduallyis increased and the effective mass is reduced,effectively manipulating the carrier concentration and mobility.Based on the high-pressure manipulationof the crystal structure and energy band structure,the electrical transport performance of BiCuSeO has been significantly improved,and the BiCuSeO sample prepared at 4 GPa exhibited a miximum power factor of?80?Wm^-1K^-2 at room temperature,which is significantly higher than that of BiCuSeO samples without pressure intervention at room temperature.(2)Band structure engineering is an effective method to improve thermoelectric performance,especially in the electrical transport properties.In this work,we used high pressure to assist Te doping achieving optimal modulation of the energy band structure in BiCuSe_1-xTe_xO.The combination of pressure and Te doping reduces the effective mass significantly,and finally obtains an ultrahigh carrier mobility of?129.6 cm²V^-1s^-1.At the same time,the density functional theory(DFT)is used to simulate the influence of pressure on the electronic structure,which is a good corroboration with the experimental results.In addition,the application of pressure further influences the optimization effect of Te doping on the carrier-phonon transport of the BiCuSeO system.The synergistic effect of high pressure and Te doping induces the multiscale microstructure characteristics,and effectively improves the phonon scattering.Hence,the as-propared BiCuSe_1-xTe_xO can obtain a low thermal conductivity of 0.3 Wm^-1K^-1.Finally,the maximum z T value of the BiCuSe_0.8Te_0.2O sample reached 0.86 at 873 K,which was an increase of?21%compared with the highest z T value of other reported BiCuSe_1-xTe_xO samples.