| BiFeO3-BaTiO3 based ceramics have both high Curie point and strong piezoelectricity,which has become one of the research hotspots in the lead-free field in recent years.In this thesis,the phase structure,microstructure,dielectric,ferroelectric,electric field induced strain,piezoelectric and leakage of BiFeO3-BaTiO3 based ceramics were investigated systematically.The micro-physical mechanism of its electrical properties was discussed.Firstly,Mn O2 was added to a high performance Ba0.985Ca0.005Ti0.98Sn0.02O3?BCTS?ceramic matrix.It was found that all samples exhibited a crystal structure in which tetragonal-orthogonal?T-O?two phases coexisted,the unit cell volume and average grain size firstly increase and then decrease.The ceramic with 0.4 mol%Mn O2 doping demonstrated an optimum comprehensive room temperature electrical properties(?r=2802,tan?=0.081,TC=121?,?max=9977,Pr=11.8?C/cm2,EC=2.6kV/cm,bipolar Smax=0.25%,unipolar Smax=0.28%,d*33=1093pm/V,d33=325 p C/N,kp=43.2%,Qm=118),which may be ascribed to the combined action of the electrical property grain size effect caused by the acceptor doping and the pinning effect of the oxygen vacancies on the domain walls.BiFeO3?BF?was introduced into BiFeO3?BT?to form a binary solid solution?1-x?Bi Fe O3-x BiFeO3??1-x?BF-x BT,x=0.26-0.34?.It was found that with the increase of the BT component content,the solid solution changed from a rhombohedral phase?R??0.26?x<0.30?to a tetragonal-rhombohedral?T-R?two-phase coexisting crystal structure?0.30?x?0.34?.The morphotropic phase boundary?MPB?component region is 0.30?x?0.34.The average grain size increases monotonically,and the unit cell volume and relative density firstly increase and then decrease.0.68BF-0.32BT component samples demonstrated an optimum comprehensive room temperature electrical properties(TC=460?,?r=725,tan?=0.834,Pmax=34.1?C/cm2,Pr=23.5?C/cm2,EC=25.6kV/cm,bipolar Smax=0.19%,total Smax=0.25%,unipolar Smax=0.22%,d*33=514 pm/V,d33=133p C/N,kp=25.1%,Qm=38),which may be due to the combined action of the grain size effect caused by solid solution and the coupling between tetragonal-rhombohedral two ferroelectric phases.Based on the above studies,0.68BF-0.32BT+x wt%Mn O2?x=0.0-0.6?ceramic samples were prepared.It was found that the introduction of Mn O2 in0.68BF-0.32BT did not change the crystal structure of T-R two-phase coexistence,the unit cell volume gradually increased,and the average grain size firstly increased and then decreased.0.1 wt%Mn O2 doping demonstrated an optimum room temperature dielectric properties?TC=462?,?r=714,tan?=0.562?;When the doping amount is 0.2 wt%Mn O2,the dielectric relaxation reached the maximum??=1.821?,and the sample demonstrated an optimum room temperature ferroelectric,electric filed induced strain and piezoelectric properties(Pmax=36.8?C/cm2,Pr=27.8?C/cm2,EC=28.2 k V/cm,bipolar Smax=0.20%,total Smax=0.27%,d33=133p C/N,kp=28.1%);0.3 wt%Mn O2 doping increases its Qm to 67.This may be ascribed to the combined action of grain size effect caused by B-site Mn acceptor doping and oxygen vacancy regulation defects.Sm2O3 was further introduced into 0.68BF-0.32BT,and 0.68BF-0.32BT+x mol%Sm2O3?x=0.0-1.5?ceramic samples were prepared.It was found that the increase of the Sm2O3 doping amount in 0.68BF-0.32BT did not change the crystal structure in which T-R phases coexisted,the unit cell volume and average grain size increase firstly increase and then decrease.0.1 mol%Sm2O3 doping demonstrated an optimum room temperature dielectric properties?TC=471?,?r=874,tan?=0.804?;When the doping amount is 0.3 mol%Sm2O3,the dielectric relaxation reached the maximum??=1.998?,and the sample demonstrated an optimum room temperature ferroelectric properties and electric filed induced strain(Pmax=34.4?C/cm2,Pr=24.1?C/cm2,EC=22.0kV/cm,bipolar Smax=0.26%,total Smax=0.32%,unipolar Smax=0.29%,d*33=740 pm/V);Sm2O3 doping makes its piezoelectric properties decrease monotonically.This may be related to the electrical property grain size effect caused by Sm2O3 doping. |
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