Preparation And Dielectric Properties Of B-site Doped Barium Titanate High Entropy Ceramic

BaTiO₃ is a common dielectric ceramic material.The dielectric constant of barium titanate varies greatly with temperature and is a non-linear relationship.Generally,under normal temperature conditions,the dielectric constant of pure barium titanate ceramics is about 2000～3000,but when the temperature reaches Curie temperature（about 120^°C）,the dielectric constant rapidly increases to around10000.However,its high-temperature stability is poor（Curie temperature is 120^°C）,and its residual polarization is high（Pr>14.7μC/cm²）,with low energy storage density and efficiency.Therefore,BaTiO₃ cannot be applied at higher temperatures（>200^°C）.This study draws inspiration from the theory of high entropy ceramics and hopes to improve the high-temperature stability of barium titanate.Two types of high entropy ceramics,Ba(Zr_0.2Ti_0.2Sn_0.2Hf_0.2X_0.2)O₃（X=Nb or Ta）,were prepared by doping the B site of BaTiO₃ at higher temperatures using conventional sintering and rapid hot pressing sintering methods(Ba(Zr_0.2Ti_0.2Sn_0.2Hf_0.2X_0.2)O₃（X=Nb or Ta）ceramic powder was prepared using a solid-state reaction method.Then,Ba(Zr_0.2Ti_0.2Sn_0.2Hf_0.2Nb_0.2)O₃ was calcined at 1250^°C for 10 hours and then sintered at 1480^°C for 2 hours using conventional sintering methods;Ba(Zr_0.2Ti_0.2Sn_0.2Hf_0.2Ta_0.2)O₃ was first calcined at 1350^°C for 10 hours,and then sintered at 1600^°C for 10 hours),respectively.The phase composition,relative density,micro morphology,dielectrical and mechanical properties of high entropy ceramics were characterized by XRD analysis,Archimedes drainage method,SEM micro morphology analysis,EDS analysis,indentation method,dielectric property analysis and other test methods.The effects of conventional sintering and rapid hot pressing sintering on the microstructure and dielectric properties of Ba(Zr_0.2Ti_0.2Sn_0.2Hf_0.2X_0.2)O₃（X=Nb or Ta）high entropy ceramics were discussed.Powders of Ba(Zr_0.2Ti_0.2Sn_0.2Hf_0.2X_0.2)O₃（X=Nb or Ta）ceramics were prepared using a solid-state reaction method,and two types of high sintering ceramics were prepared using traditional sintering methods.XRD testing showed that the two Ba(Zr_0.2Ti_0.2Sn_0.2Hf_0.2X_0.2)O₃（X=Nb or Ta）ceramics have a single-phase perovskite structure and no diffraction peaks of other impurities.The average grain size of conventional sintered Ba(Zr_0.2Ti_0.2Sn_0.2Hf_0.2X_0.2)O₃（X=Nb or Ta）ceramics is 0.70μm and 1.30μm.The breakdown field strengths of Ba(Zr_0.2Ti_0.2Sn_0.2Hf_0.2X_0.2)O₃（X=Nb or Ta）tested by a ferroelectric analyzer were E=100 k V/cm and E=50 k V/cm,respectively.Through dielectric performance testing,at 25～400^°C,the dielectric constants of Ba(Zr_0.2Ti_0.2Sn_0.2Hf_0.2X_0.2)O₃（X=Nb or Ta）is 44.99～47.08 and 49.78～50.49,respectively;The dielectric losses of Ba(Zr_0.2Ti_0.2Sn_0.2Hf_0.2X_0.2)O₃（X=Nb or Ta）ceramics is 0.13085～1.334 and0.074～0.222,respectively.The Vickers hardness of Ba(Zr_0.2Ti_0.2Sn_0.2Hf_0.2X_0.2)O₃（X=Nb or Ta）is 8.40MPa·m^1/2 and 5.20 MPa·m^1/2 respectively,and the fracture toughness of Ba(Zr_0.2Ti_0.2Sn_0.2Hf_0.2X_0.2)O₃（X=Nb or Ta）is 2.74 MPa·m^1/2 and 2.25MPa·m^1/2 respectively.In order to improve the dielectrical and mechanical properties of Ba(Zr_0.2Ti_0.2Sn_0.2Hf_0.2X_0.2)O₃（X=NborTa）ceramics,Ba(Zr_0.2Ti_0.2Sn_0.2Hf_0.2Nb_0.2)O₃ and Ba(Zr_0.2Ti_0.2Sn_0.2Hf_0.2Ta_0.2)O₃ high entropy ceramics were prepared by sintering at 1480^°C and 1400^°C for 5 minutes,respectively,and their dielectric properties were studied.The relative density of ceramics using rapid hot pressing sintering method is 97.20%and 92.89%,respectively,with an average grain size of 0.88μm and 141.23 nm.The breakdown field strengths of Ba(Zr_0.2Ti_0.2Sn_0.2Hf_0.2Ta_0.2)O₃（X=Nb or Ta）were tested using a ferroelectric analyzer,with E=30 k V/cm and E=23 k V/cm,respectively.Through dielectric property testing,at 25 to 400^°C,the dielectric constant of Ba(Zr_0.2Ti_0.2Sn_0.2Hf_0.2Nb_0.2)O₃ is 20～350,and the dielectric loss is 0.13085～1.334.The dielectric constant of Ba(Zr_0.2Ti_0.2Sn_0.2Hf_0.2Ta_0.2)O₃ is 900～2600,and the dielectric loss is 1～12.The Vickers hardness of Ba(Zr_0.2Ti_0.2Sn_0.2Hf_0.2X_0.2)O₃（X=Nb or Ta）is 7.45MPa·m^1/2 and 5.22 MPa·m^1/2,respectively.The fracture toughness of Ba(Zr_0.2Ti_0.2Sn_0.2Hf_0.2X_0.2)O₃（X=Nb or Ta）is 2.99 MPa·m^1/2 and 2.12MPa·m^1/2 respectively.