Preparation Of In₂O₃(ZnO)_k Ceramics And Their Thermoelectric Properties

Thermoelectric material is one of the functional materials,which can achieve a direct interconversion between thermal energy and electric energy by the movements of carriers,and it can be used in thermoelectricity generation and cooling.Global environmental deterioration and energy crisis were increasingly serious and they threaten human life,so it is an urgent problem to look for a new green environmental energy.Fortunately,thermoelectric material is appeared and it is one of the hot spots of new energy materials.The equipments of power generation and cooling have some advantages,including noise-free operation,compact structures,non-pollution,great reliability and long operating life so on.And it can be used in civil,military and aerospace fields.Besides,oxide thermoelectric materials are a new research directions in thermoelectric materials own to low costs for raw materials,stability under high temperature and non-pollution.In this thesis,the environment-friendly In₂O₃?ZnO?_k ceramics of thermoelectric materials are mainly studied,and the effects of different preparation processes on the thermoelectric properties were researched.Firstly,In₂O₃?ZnO?_k?k=3,4,5,7?ceramic blocks were successfully prepared at 1473-1623 K by using the traditional solid-phase sintering method.Based on phase structure and microstructure analysis,In₂O₃?ZnO?_k?k=3,4,5,7?ceramics were layered super-lattice structures.The super-lattice structures of all samples were formed by stacking InO₂^-octahedron and InO?ZnO?₃⁺layers alternately in the c-axis direction.With the increase of k value,the thickness of InO?ZnO?₃⁺in the crystal gradually increases,but the value of band gap gradually decreases.In₂O₃?ZnO?₃ ceramic obtained the largest power factor of 651?Wm^-1K² and the maximum ZT value of 0.24 at 973 K.Secondly,the effects of different holding times on the thermoelectric properties of In₂O₃?ZnO?₅ ceramics were studied.It was found that there were In₂O₃?ZnO?₇ impurity phase when the holding times are 6 h,8 h and 10 h samples,respectively.When the holding time was 15 h,the impurity phase appears in the sample and corresponds well to In₂O₃?ZnO?₄.Only the sample with 12 h holding time was In₂O₃?ZnO?₅ pure phase.The potential loss of In and Zn with extending the holding time in the sample,and the conductivity and seebeck coefficient of the material will be affected.Defects caused by the missing atoms increasing lattice scattering and the thermal conductivity of materials reduced.The maximum thermoelectric value of 0.19 was detected with 12 h holding time sample at 973 K.Based on the above experiments,the thermoelectric properties of Ni modified In₂O₃?ZnO?₅ were studied.In this paper,a mechanism model for deposition process was put forward,and it demonstrated that[bmim]BF₄ additive was more prone to be adsorbed on the protrusions and sharp points of In₂O₃?ZnO?₅ surface which inhibit the fast nucleation and crystal growth of Ni,it benefit to obtain uniform Ni modified In₂O₃?ZnO?₅ powders.Following that,Ni/In₂O₃?ZnO?₅ core-shell bulk samples were synthesized by spark plasma sintering.The results found that the ZT value increased from 0.12 for pure In₂O₃?ZnO?₅ to0.39 for Ni modified In₂O₃?ZnO?₅ core-shell bulk material.And the increase was mainly due to the enhancement of Fermi level for Ni modified In₂O₃?ZnO?₅ core-shell bulk material.