Study On Preparation And Properties Of LaAlO₃ Perovskite High-entropy Ceramic Materials

High entropy ceramics are solid solutions of inorganic compounds,which have one or more occupation sites and are shared by the same or nearly the same atoms of main elements.LaAlO₃ is a common perovskite ceramic material with good dielectric properties and high temperature stability.It is a very important single crystal material for high temperature superconducting thin film substrate.It also has great research and development value in high temperature superconducting microwave electronic device technology.In this thesis,LaAlO₃ was used as the matrix,a site was doped,and the design idea of high entropy ceramics was introduced.On the basis of maintaining its low dielectric constant and low dielectric loss,the functional ceramics with low thermal conductivity and good mechanical properties were obtained,and their photocatalytic properties were explored.The solid phase method is used to prepare(Y_0.25Gd_0.25La_0.25M_0.25)AlO₃（M=Nd,Sm,Eu,Dy）high-entropy ceramics with oxides as raw materials.The optimized process conditions are 1300℃for 1h,and the products are all perovskite structure.The unit cell parameters decrease as the radius of the M ion decreases.The prepared high-entropy ceramic material exhibits certain mechanical properties.Among them,(Y_0.25Gd_0.25La_0.25M_0.25)AlO₃ high-entropy ceramic has the best flexural strength,which is 277.46 MPa;(Y_0.25Gd_0.25La_0.25Sm_0.25)AlO₃ high-entropy ceramic has the best elastic modulus,which is 100.45 GPa;(Y_0.25Gd_0.25La_0.25Sm_0.25)AlO₃ high-entropy ceramic has the best Vickers hardness,which is 796.08HV20.Using sol-gel method to prepare(Y_0.25Gd_0.25La_0.25M_0.25)AlO₃（M=Nd,Sm,Eu,Dy）high-entropy ceramics with metal nitrate as raw materials,the optimized process conditions are 1000℃for 1h,the products are all perovskite structures.In the photocatalytic degradation performance test of Rhodamine B,(Y_0.25Gd_0.25La_0.25M_0.25)AlO₃ has better degradation performance than pure LaAlO₃,reaching 96.89%,and the degradation rate constant is 0.01771min^-1.The photohydrogen production rates of the four systems are 701μmolg^-1h^-1,832μmolg^-1h^-1,1052μmolg^-1h^-1,1628μmolg^-1h^-1,respectively,which are better than the performance of single-phase LaAlO₃.High-entropy ceramics have lower thermal conductivity,while maintaining the low dielectric constant and low dielectric loss of LaAlO₃.(Y_0.25Gd_0.25La_0.25M_0.25)AlO₃（M=Nd,Sm）high-entropy ceramic nanofibers prepared by electrospinning method,the optimized process conditions are 1000℃for1h,and the products are all perovskite structures.The fiber diameter is approximately130 nm.Compared with the high-entropy ceramic samples prepared by the sol-gel method,the photocatalytic performance is improved.The degradation rate of(Y_0.25Gd_0.25La_0.25Sm_0.25)AlO₃ to degrade rhodamine B reached 97.96%.The rate of hydrogen production by photolysis of water was 909μmolg^-1h^-1 and 1587μmolg^-1h^-1,respectively.