| Electronic ceramics are widely used in the fields of communication,storage,electronic industry and automation for their unique electrical,optical and magnetic properties.Up to now,BiFeO3 and its compounds account for almost 1/3 of the known multiferroic materials,which are commonly applied as multiferroic materials at room temperature.However,BiFeO3 and BiFeO3 based compounds have some inherent problems,such as large leakage current and weak ferromagnetism.Introducing BaTiO3 into BiFeO3 to form a solid solution can reduce the leakage current and enhance the magnetic properties.So far,BiFeO3-BaTiO3(BF-BT)has become the fourth promising lead-free piezoelectric ceramic system.To study the nature of the polar state in the morphotropic phase boundary composition 0.67BF-0.33BT,solid solution ceramics(1-x)BF-xBT-0.01MnO2 were prepared by the solid-state reaction method.When the content of BaTiO3 is 20-25 mol%,(1-x)BF-xBT exhibits an rhombohedral structure.And it exhibits an pseudo-cube structure with the content of BaTiO3 up to 25-41 mol%.With the increasing of BaTiO3,its ferroelectricity decreases gradually and the relaxation enhanced.As for the morphotropic phase boundary composition 0.67BF-0.33BT,the relationship between the dielectric constant and temperature shows typical relaxor ferroelectric characteristics(Tf=～627 K,TB=～820 K).Both the unpoled and poled specimens exhibit an pseudo-cubic structure.Macro-domains are absent both in the initial and polar states of 0.67BF-0.33BT,and the poling induces a 0.14%increase in the lattice parameter.From 298 to 453 K,the remnant polarization(Pr)and maximum value of electro strain(Sm)increase clearly during heating(Pr,～40 μC/cm2;Sm,0.191%under 40 kV/cm at 453 K).The first-cycle bipolar electrostrain loops indicate that the minimum strain on the negative side of the bipolar strain curves is negative.The dielectric constant is obviously dependent on the frequency,and the frequency dispersion behavior does not change after polarization.The transition between the relaxor state and ferroelectric-like state does not involve an obvious dielectric anomaly even in the poled specimens.To study quenching effects on phase structure,electrical and magnetic properties,0.8BF-0.2BT ceramics were prepared by quenching and cooling with furnace.The lattice parameter(unquenched,aR=3.9899 A;quenched,aR=3.9934 A)and rhombohedral distortion angle of 0.8BF-0.2BT(unquenched,αR=89.54°;quenched,αR=89.58°)increase through quenching technology.The dielectric loss of the unquenched samples is 0.231(1 kHz)at room temperature,while the dielectric loss of the quenched samples is only 0.039,which is reduced by about 83%.More importantly,no non-intrinsic dielectric anomalies appear near 550 K and 900 K.After being quenched,the polarization electric curve of the samples barely affected by the leakage current,and the samples show a large electrostriction.The relationship between conductivity and temperature indicates that intrinsic carriers have a major influence on the conductivity of the samples at the temperature range of 473-643 K after quenching,and a sudden change of conductivity exists near the Curie point.The unquenched samples show better magnetic properties,which is more likely to be related to non-intrinsic factors.Lead-free(0.86-x)BF-xBT-0.14AN ceramics were prepared by the thermal quenching technique.The main phase of all BF-BT-AN samples has cubic symmetry.All samples exhibit obvious relaxor behavior.The unipolar polarization responses of each composition are similar.0.56BF-0.3BT-0.14AN shows a optimum energy storage density at high frequency(Wrec=0.667 J/cm3,η=64.2%).The poor energy storage characteristics of this system are likely related to the narrow bandgap. |
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