Study On Synthesis Of Ba_1-xSr_x(Ti_1-yNb_yO₃)and Optical&Dielectric Properties

The variation of Curie temperature of BaTiO₃ is one of the most important properties of BaTiO₃.Due to its tetragonal-cubic phase transition characteristics and high dielectric constant,BaTiO₃ materials play an important role in many fields.In this paper,BaTiO₃,SrCO₃,TiO₂ and Nb₂O₅ powders were used as raw materials to prepare Ba_1-xSr_x(Ti_1-yNb_yO₃)by high temperature solid phase synthesis.The effects of preparation process and doping concentration on the lattice structure and phase transition properties of the product were investigated.The properties of dielectric,optical,anti-irradiation and infrared radiation were characterized.The mechanism of performance change was discussed.Evaluation of the application prospects of thermal control coatings.The Ba_1-xSr_x(Ti_1-yNb_yO₃)powder synthesized by ball milling,heat preservation and calcination at 1450°C has the highest tetragonality.Sr and Nb doping can lower the Curie temperature of BaCO₃ to room temperature,the peak shift efficiency of Sr is about-3.3°C,and the peak shift efficiency of Nb is about-22.5°C.With the increase of Sr and Nb doping amount,the phase transition amplitude and the accompanying phase change latent heat also decreases.Sr doping results in a decrease in lattice volume,while Nb doping results in an increase in lattice volume.The result of doping causing lattice distortion is as follows:the lattice a and b axes are elongated,the c-axis is shortened,and the tetragonal rate parameter c/a is continuously reduced.The theoretical calculation results show that the synthesized material has a higher tetragonality when the doping element enters the tetrahedral gap position in the Ba_1-xSr_x(Ti_1-yNb_yO₃)perovskite structure.As the temperature decreases,the crystal structure of the Ba_1-xSr_x(Ti_1-yNb_yO₃)phase changes sequentially from cubic phase to tetragonal phase→orthogonal phase→trigonal phase.The reflectivity of Ba_1-x-x Sr_x(Ti_1-yNb_yO₃)decreases slightly with the increase of Sr doping content,and increases slightly with the increase of Nb doping content,but has no essential effect on the optical properties of Ba_1-xSr_x(Ti_1-yNb_yO₃).The Ba_1-xSr_x(Ti_1-yNb_yO₃)powder exhibits excellent radiation stability by proton irradiation.With the increase of Sr content,the infrared absorption characteristic peak of Ba_1-xSr_x(Ti_1-yNb_yO₃)is blue-shifted and close to the atmospheric window range（8-14μm）.As the Nb content increases,the infrared absorbance decreases,which is beneficial to radiate more outward.Heat.As the temperature increases,the absorbance of Ba_1-xSr_x(Ti_1-yNb_yO₃)decreases,and the characteristic peak of Ba_1-xSr_x(Ti_1-yNb_yO₃)is red-shifted,away from the atmospheric window,which is beneficial to reduce the absorption of infrared heat.In the atmospheric window,the infrared emissivity of Ba_1-xSr_x(Ti_1-yNb_yO₃)decreased slightly with the increase of Sr and Nb doping content,but remained at about 0.88.The Sr and Nb dopings reduce the dielectric constant,decrease the Curie temperature,and slow the Curie peak.The above results show that Ba_1-xSr_x(Ti_1-yNb_yO₃)has low solar absorption ratio,high infrared emissivity and radiation stability.Moreover,by adjusting the doping contents of Sr and Nb,the phase transition temperature,the solar absorption ratio and the infrared emissivity can be adjusted to some extent,and the potential for further development as a thermal control material is obtained.