The Preparation And Thermoelectric Properties Of Ruddlesden-Popper Phase Barium Titanate

Barium titanate exhibits high thermoelectric properties among the oxide thermoelectric materials,due to its high temperature stability and large Seebeck coefficient.Therefore barium titanate shows great research value and application potential in the field of high temperature waste heat recovery.Ruddlesd-Popper structure barium titanate owns natural layered structure,which can effectively scatter phonons and reduce the thermal conductivity;also by heavy doping the cubic structure barium titanate can realize from semiconductor performance to metal performance,and shows good electrical conductivity.Based on this,the Ruddlesd-Popper structure Sr_n+1Ti_nO_3n+1 and Nb-doped barium titanate SrTi_1-xNbxO₃ were prepared by molten salt method and solid-state methods.The Nb-doped barium titanate is used as the conductive matrix phase,and the Ruddlesd-Popper structure barium titanate is used as the phonon scattering center,in this way,we can construct a material structure with multi-level phonon scattering centers without reducing the conductivity.And achieved a significant reduction in thermal conductivity of such materials.Firstly,in this paper,SrCO₃?TiO₂ and butyl titanate were used as raw materials,by sol-gel method.By 0.1 mol Sr_n+1Ti_nO_3n+1?n=1?synthesized,the content of citric acid was1.4¹.6 times in mass of the total of metal ions,and use 500 ml of deionized water and absolute ethanol,and the content of deionized water and absolute ethanol is 1:1 in mass.The best sintering temperature is 1000? and the holding time is 4 h,the average particle size of the sample is 63.2 nm.Secondly,Sr_n+1Ti_nO_3n+1?n=2?was prepared by molten salt method,the SrCO₃,TiO₂ and NaCl is used as raw materials.The best preparation process is 1200? and hold the time for 4hours,during the experiment.we find that Ruddlesd-Popper structure barium titanate is very sensitive to Sr:Ti?mass ratio?in the raw material,and Sr²⁺is required to be excessively 1.2times during the preparation.Then we discuss the influence of different type solvent,NaCl was selected as the solvent for subsequent preparation.By controlling the content of NaCl in molten salt,The results demonstrate that control of the thickness in c-axis of Sr_n+1Ti_nO_3n+1?n=2?material can be easily achieved by varying the added amount of the molten salt In addition,we also explore the raw material molten salt pretreatment.It can be concluded that the molten salt environment is very conducive to the growth of the crystal.The synthesis of the material is closely related to the size of the raw material.At the same time,we synthesis the hollow sphere.Barium titanate,which provides some ideas for follow-up researchers.Finally,SrTi_1-xNb_xO₃?x=0.1?0.15?0.25?0.3?was prepared by conventional solid-state method using SrCO₃,using TiO₂ and Nb₂O₅ as raw materials?under anoxic conditions during heat treatment?,and then combined with Ruddlesd-Popper structure.After Sr_n+1Ti_nO_3n+1?n=2?is mixed in some certain proportion,the anisotropic coating is prepared by casting method,and the embossing is performed after heat treatment to prepare the required strong phonon scattering.To the heterogeneous barium titanate material,the comparison of the thermoelectric figure of the products in different proportions was investigated,and the sintering temperature was determined to be 1200-1500?.It is found that with the increase of Nb⁵⁺content,the electrical conductivity of the material increases,and the mass ratio is Sr₃Ti₂O₇:SrNb_0.3Ti_0.7O₃=2:10 casting.The room temperature thermal conductivity is 2W·m^-1·K^-1.Around-1,the thermal conductivity of the material is significantly reduced,which is helpful for the improvement of the thermoelectric figure of the barium titanate thermoelectric material,and also provides a new idea for reducing the thermal conductivity of the oxide material.