Preparation And Thermoelectric Of Cobalt Base Thermoelectric Oxides

As one of the functional materials for energy conversion between thermal and electrical energy with using solid interior current carrier moving, thermoelectric material has important application value and widespread application prospect in the thermoelectric generation and thermoelectric refrigeration field. Energy shortage and environmental problems greatly promoted the thermoelectric materials.Today, most of high performance thermoelectric materials contain toxic element, such as Te,Sb,Pb,etc., Therefore, there are hight cost and environmental pollution problems during the production. As the discovery of oxide high-temperature superconductors "unexpectedly" in 1986, breaking the formal thinking that we should search superconductor in metal material system, Professor Terasaki in Waseda University, has first pointed out NaCo2O4 can be a new thermoelectric material which has "abnormal" high properties in 1997. The metal oxide thermoelectric materials,which has been forgotten over the past few decades, are entering the field of researchers' vision. Thermoelectric oxide, more and more widely attentioned, is a class of good perfomance thermoelectric matericals with the advantages of varieties, low cost of raw materials, nontoxic, pollution-free, simple process, stable performance under high temperature.Two cobalt-based oxides were gropingly synthesized by solid state reaction and hydrothermal method. We have studied their crystal structure, chemical component and the thermal and electronic transport properties. We also have evaluated the possibility of thermoelectric application. The main results were obtained as following:(1)ZnCo₂O₄ is a typical cobalt spinel oxide. Previous research about ZnCo₂O₄ focused on the electrical properties of composite electrode. We first take ZnO,Co₂O₃ as experimental materials,synthesized ZnCo₂O₄ by solid state reaction,The phase and structure of the oxides are characterized by XRD。The reaction is not complete under 1300℃, which can not produce materials.(2)When we replace Co3O4 with Co₂O₃ as raw materials, we still can not target resultant ZnCo₂O₄,even if we changed the reaction time and temperatures.(3) Single-phase ZnCo₂O₄ is successfully synthesized by hydrothermal method at low temperatures (180℃-120℃)by using Co(NO₃)₂·6H₂O,ZnCl₂,NaOH as starting materials. We analyzed phase and morphology of sample by XRD and SEM respectively; After sintered the powder materials by spark plasma sintering method, We tested and analyzed the thermoelectric properties of the samples by measuring high temperature electrical conductivity, thermal conductivity and Seebeck coefficient. It has a high seebeck coefficient of 550μV/K, low thermal conductivity of 4.5W/mK and very low electricalconductivity of 15S/m at 650 K.(4) In this study, we innovatively synthesized Co₃O₄ by hydrothermal method, using Co(NO₃)₂ï¹’6H₂O, NaOH as raw materials. After sintered the powder materials by spark plasma sintering method, we analyzed phase composition by XRD, tested and analyzed the high temperature conductivity, thermal conductivity, seebeck coefficient of it. The maximum Seebeck coefficient and electrical conductivity is 220μV/K and 110 S/m, respectively.