| BiFeO3-BaTiO3?BF-BT?solidsolutionsattractedgreatattentionas environmental friendly lead-free piezoelectric materials because of their high Curie temperature as well as multiferroic properties.Nowadays,the results of structures and compositions in the vicinity of phase boundary for pure BF-BT ceramics were various.The dielectric loss of BF-BT ceramics was still large,and there were few papers involved in basic dielectric,ferroelectric and piezoelectric properties.The insulativity of modified BF-BT ceramics was enhanced,however,the dielectric loss were still large and the ferroelectric and piezoelectric properties of modified BF-BT ceramics were needed to be improved.Furthermore,the high temperature dielectric and piezoelectric properties were rarely reported.In this paper,the perovskite lead-free piezoelectric BF-BT ceramics were fabricated by conventional solid-state reaction method,the compositions of phase boundary were defined,meanwhile,the effects of Mn addition,O2 atmosphere sintering,quenching process and Nb modification on dielectric,ferroelectric and piezoelectric properties of BF-BT ceramics in the vicinity of phase boundary.The mainly results are as follows:?1??The effects of BF contents on structure,micro-structure,dielectric,ferroelectric and piezoelectric properties for xBF-?1-x?BT?x=0.67,0.69,0.70,0.71,0.73,0.75?ceramics were investigated.XRD analysis indicated that the ceramics with x<0.69 were in the typically pseudo-cubic phase,Coexistence of rhombohedral phase and pseudo-cubic phase were observed in the compositions with 0.69?x?0.73,which belongs to phase boundary compositions.As x was above 0.73,BF-BT ceramics exhibits rhombohedral phase.With the increase BF contents,the grain sizes of increased from 5?m?x=0.67?to 8?m?x=0.75?,and the Curie temperature increased from 470oC?x=0.67?to 590 oC?x=0.75?.The piezoelectric constant increased firstly and then decreased,the piezoelectric constant of 0.71BF-0.29BT ceramics within phase boundary were highest,which was 75 pC/N.?2??The addition of Mn did not change the structure of 0.71BF-0.29BT ceramics,but could improve the sintering process.With the increase Mn contents,the grain sizes increase,the dielectric loss increase initially and then decrease,ferroelectric and piezoelectric properties were enhanced firstly and then deteriorated.The ceramics with 1.2 mol%Mn addition exhibit the best compatible properties,whose dielectric loss tan?,Curie temperature TC,depolarization temperature Td,remanent polarization Pr,unipolar strain Smax were 0.042,506 oC,500 oC,30.4?C/cm2,0.27%,respectively.The high field piezoelectric constant for BF-BT-1.2mol%Mn ceramics was 525 pm/V with 200oC under 40 kV/cm,the largest strain Smax and strain hysteresis Hrel were0.21%and 28%,respectively.?3??O2 atmosphere sintering and quenching process had little effects on structure of ceramics.With O2 atmosphere sintering and quenching,the grain sizes were larger and more homogeneous,the dielectric loss decreased,insulation enhanced,ferroelectric and piezoelectric properties were improved.The resistivity of O2 sintered BF-BT-0mol%Mn ceramics at 573 k was 600 k?.cm,about 11 times of that air sintered ones,the resistivity of BF-BT-1.2mol%Mn ceramics increased to 3150k?.cm.The unipolar strain,d*33,d33 of BF-BT-0.5mol%Mn ceramics increased from0.09%to 0.22%,119 to 284 pm/V,82 to 152 pC/N for sintered in O2 and air.The tan?of quenched BF-BT-0.3mol%Mn ceramics at 500oC was 0.28,which was only 1/5.5of that the slow cooling ones.The resistivity of quenched BF-BT-0.3mol%Mn ceramics was two times of the slow cooling ceramics.The strain S,piezoelectric constant d33,increased from 0.073%to 0.293%,75 to 191 pC/N after quenching.The quenching process improved the extrinsic contribution for dielectric and piezoelectric responds.?4??The effects of Nb partly substitute B site ions?Fe and Ti ions?of BF-BT-1.2mol%Mn ceramics on structure and properties were consistent.BF-BT-1.2mol%Mn ceramics exhibited coexistence of rhombohedral phase and pseudo-cubic phase,while Nb doped to substitute Fe and Ti ions BF-BT-1.2mol%Mn ceramics exhibited single pseudo-cubic phase.The grain size of ceramics decreased with the Nb doping,meanwhile,the dielectric loss tan?increased and the ferroelectric and piezoelectric properties were deteriorated. |
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