Preparation And Performance Optimization Of CdO-based Thermoelectric Materials

Thermoelectric materials can directly realize the mutual transformation between thermal energy and electric energy.Thermoelectric materials have been received extensive attention owing to broad development prospects in the fields of thermoelectric refrigeration and thermoelectric power generation.Due to the good chemical stability and thermal stability in high temperature air environment,low requirements for the working environment,low raw material cost and simple preparation process,Oxide thermoelectric materials have the potential application value in the high temperature environment.This paper mainly studied the n-type cadmium oxide?CdO?thermoelectric material.In order to improve the CdO thermoelectric conversion efficiency,the doping of ZnO,ZnCO₃ and Cu was used to optimize the electrical properties and thermal properties of CdO materials.The research content of this study mainly includes the following three aspects:1.Doping of ZnO on the Thermoelectric Properties of CdO Materials.In the ZnO doping process,the introduced Zn²⁺part enterd into the interstitial sites or Cd²⁺vacancies,resulting in increased carrier concentration,increased electrical conductivity,and optimized power factor?PF?.In addition,the point defects,the Zn-rich second phase and the increased grain boundaries introduced by Zn²⁺doping enhanced phonon scattering,effectively reduced the thermal conductivity of CdO ceramics,and the power factor and thermal conductivity were optimized at the same time.Ultimately,the thermoelectricity of CdO materials was improved.The value of merit?ZT?was increased by 32%.2.The Zn²⁺doped CdO ceramic with porous structure was prepared through the co-sintering process of ZnCO₃ and CdO,which not only maintains the power factor but also further reduces the lattice thermal conductivity.The ZT value was increased by 53%compared to the intrinsic CdO.There were two advantages to using ZnCO₃ instead of ZnO as doping source:?1?ZnO had a higher melting point?2248 K?,while ZnCO₃ was decomposed into ZnO and CO₂ at 573 K,which increased the solid solubility of Zn²⁺ions;?2?CO₂produced by the decomposition of ZnCO₃ increased the porosity of the sample.The increased microporosity can act as a scattering center to scatter the medium-long wavelength phonons,which further reduced the thermal conductivity.3.Using co-sintering of Cu and CdO,CdO?Cu_x composite ceramic with a constant carrier concentration but a two-fold increase in mobility was prepared.The power factor of the sample was optimized and eventually the thermoelectric performance of the CdO material was improved.Unoxidized Cu particles between CdO grains in this sample might serve as carrier channels and increased the carrier mobility.