First-principles Calculation And Preparation Of Copper Beryllium Oxide-based Thermoelectric Materials And Doping Thermoelectric Properties

The energy shortage and environment population are two major challenges of the 21th century owing to the rapid urbanization and industrialization.In order to solve these two problems,alternative energy and new energy materials are needed.Thermoelectric material is an emerging functional material that can convert the heat into electricity directly,which have attracted a wide range of attention.Among all thermoelectric materials,cobalt-base oxides are particularly promising,because they are nontoxic,taintless,and very stable at high temperature,which is attractive for application in waste heat recovery,solar energy harversting,and heat management.In this thesis,the research progress and application of thermoelectric materials was illuminated firstly.Then cobalt-base ceramic oxide of thermoelectric materials was studied as the main object.The research was fouced on the fabrication,fundamental physical properties,and characterization the thermoelectric properties.Doping,nanocomposites and low-dimension method were used to improve the thermoelectric properties.The main research works and key results are summarized as follows.The preparation of samples and experimental equipments used for testing the thermoelectric properties were introduced first(SEM,X-ray,LFA,ZEM).The lattice thermal conductivity of CuRh2-2xM2xO4 and CuRh1-yMyO2(M=Cr?Co?Mg,x?y=0,0.05,0.1,0.15,0.2,0.25,0.3)were selected to calculate the phase transformation process by the CASTEP module in MS software.The calculation results show that,the lattice thermal conductivity of the material were reduced by three kinds of dopant elements,and decreased with the increase of the doping amount;the best effect dopant element is Mg.The results show that CuRhO2 is the high temperature phase of CuRh2O4,the optimum sintering temperature of CuRh2-2xMg2xO4 and CuRh1-yMgyO2 at 940? and 980?,respectively,the doping samples are prepared by solid state reaction method.But in order to improve the thermoelectric properties and testing needs,continue to carry out the discharge of the sample plasma sintering.A series of CuRh2-2xMg2xO4 bulk samples were obtained by doping the Mg sites by two-step solid-state reaction-discharge plasma sintering.The effects of doping on the phase,morphology and thermoelectric properties of the composites were analyzed.The experimental results show that the micro-doping has little effect on the structure and phase of the matrix.When x>0.25,there may be a second phase precipitation between the grain boundaries,which affects the electrical properties of the material,resulting in a decrease in power factor.The thermal conductivity,the Seebeck coefficient and the conductivity of CuRh2-2xMg2xO4 decrease with the increase of doping amount,and the highest power factor is CuRh1.6Mg0.4O4(165.53?gW/mK-2 at 900?),but the highest ZT value is CuRh1.5Mg0.5O4,at 900? ZT maximum value:0.18.A series of CuRh1-yMgyO2 bulk samples were prepared by two-step solid-state reaction-discharge plasma sintering method,and their thermoelectric properties were characterized.The experimental results show that the prepared powder has obvious lamellar structure.After SPS sintering,the density of the bulk sample is more than 90%of the theoretical density,and the grain size decreases with the increase of Mg doping amount.The thermal conductivity of the samples decreases with the increase of the doping amount,but the Seebeck coefficient and the conductivity increase with the increase of the doping amount.CuRh0.7Mg0.3O2 ZT value of the highest,900? maximum 0.21.In this thesis,environmentally friendly oxide thermoelectric materials copper-rhodium-based oxide thermoelectric materials have been systematic investigated.The thermoelectric transportation is improved in different degrees by several methods,such as elements doping and optimization of preparation conditions.These research results show that copper-rhodium-based oxide thermoelectric materials are great potentiality material system,and bear much research value and application prospects.Meanwhile,these results have provided useful theoretical and technological references for the research and development of copper-rhodium-based oxide thermoelectric materials with high properties.