| The piezoelectric materials,as a type of functional materials with a relatively wide range of applications and a large output,the lead-free piezoelectric materials have become an urgent need in the current society where environmental protection requirements are getting higher.The BaTiO3（BT）-based lead-free piezoelectric ceramics are one of the three types of lead-free piezoelectric ceramics that have been studied more.Through the A-site and B-site ion doping,it is found that the piezoelectric performance has been greatly improved,and it has both typical ferroelectric properties and excellent dielectric properties.It is expected to get practical applications to replace toxic lead-based piezoelectric materials.This thesis selects Ba0.85Ca0.15Ti0.9Hf0.1O3（BCTH）ceramics,which is less studied,and more systematic research on it is conducted from three aspects.In the first part,we prepared BCTH ceramics doped with 0.01mol%～1mol%of rare earth ion Eu3+.The incorporation of Eu3+brings fluorescent properties into ceramics,in which the microstructure,dielectric properties,ferroelectric properties,piezoelectric properties and fluorescent properties induced by Eu doping with different amount were studied in detail.It has the potential of luminescent materials with piezoelectric properties.All the Eu-BCTH lead-free piezoelectric ceramics prepared at a sintering temperature of 1450℃ for 4 hours show a density of more than 93%,the ceramics’ microstructure is relatively dense,and the grain size is larger,～10μm.The element distribution is relatively uniform and has a relatively pure pseudo-cubic phase perovskite structure.The only peak appears in the dielectric temperature spectrum when the temperature rises,and the frequency dispersion phenomenon near Tc will gradually disappear with the increase of Eu content,indicating that the Eu-BCTH ceramics are normal ferroelectrics with dispersive phase transition characteristics.The piezoelectric and fluorescent properties are the best when the Eu doping amount is 0.5mol%,in which d33=316.6pC/N（poling electric field 2000V/mm）,the strongest fluorescence emission peak is at 689nm,emitting yellow light,corresponding to 5D0→7F3 electronic transition.With the increase of Eu doping,the emission peak intensity gradually increases.In the second part,0.5mol% Eu-doped BCTH ceramics were obtained by conventional solid-state method sintered at different sintering temperatures（1430℃～1480℃）.The effects of sintering temperature on the microscopic morphology,phase structure,electrical properties and fluorescence properties of the rare earth-doped BCTH ceramics were studied.All the samples present a pure pseudo-cubic phase perovskite structure,and the position of the diffraction peak has almost no change,indicating that the sintering temperature has little effect on the phase structure of the rare-earth Eu-doped ceramics.With the increase of the sintering temperature,the density shows a trend of first increasing,then decreasing and increasing.The density difference of the samples sintered at 1440℃ and 1480℃ is only 0.12%,the maximum density is 93.56%,and the average grain size changes from 13.8μm increased to 14.48μm.The dielectric constant has the same change trend as the fluorescence luminescence intensity:it first decreases and then increases with the sintering temperature increases.The dielectric properties of the samples sintered at 1430℃ are the best:Tc=84℃,εm=13923,and the luminescence intensity at 1430℃ is greater than 1440℃ and 1450℃.Piezoelectric performance is poor when the sintering temperature is lower than 1440℃,while the d33 of the sample sintered at 1440℃ reaches 334pC/N,which exceeds 1450℃ sintered ceramics.The third part discusses the influences of Ca2+ and Hf4+composition and sintering temperature adjustment on the Eu-BCTH lead-free piezoelectric ceramics.[（Bai-xCax）0.995Eu0.005]（Ti1-yHfy）O3（B1-xCxT1-yHy-Eu）lead-free ceramics were fabricated by conventional solid-state method,in which the effects of sintering temperature and the ratios of Ca2+ and Hf4+ions around the morphotropic phase boundary（MPB）on the electrical and fluorescent properties were explored.Since the samples sintered at 1440℃show higher performance,the sintering temperature range is selected at 1440～1460℃.The density of all samples will suddenly decrease when the sintering temperature is increased to 1460℃,except for[(B a0.85Ca0.15)0.995Eu0.005]（Ti0.91Hf0.09）O3 ceramics with y=0.09.At different sintering temperatures,the remnant polarization（Pr）shows completely different change trend with the change of the composition,and all the hysteresis loops show typical ferroelectric characteristics.When the Ca2+composition increases from 0.14 to 0.16,the Pr changes.This is because the doping of rare earth ions in BCTH ceramics produces complex point defects,which are manifested as donor doping characteristics,are conducive to polarization rotation and improve ferroelectric properties.Using the concept of figure of merit,it can be found that the[（Ba0.86Ca0.i4）0.995Eu0.005]（Ti0.9Hf0.1）O3 ceramics at a sintering temperature of 1450℃ have the best piezoelectric and fluorescent properties,as well as excellent dielectric properties:Tc=84℃,εm=11732.The Eu-BCTH lead-free piezoelectric ceramics show excellent piezoelectric and fluorescent properties when the composition is close to the morphotropic phase boundary.The dielectric properties are complex,but they have a higher dielectric constant and Curie temperature.The ferroelectric performance is good.When the temperature exceeds 250℃,it has two conductive mechanisms,and as the temperature increases,the resistance value decreases.The Eu-BCTH ceramics sintered at 1440℃obtained higher density and excellent comprehensive performance,so the Eu-BCTH lead-free piezoelectric ceramics have great potential in the field of piezoelectric-fluorescent multifunctional applications. |
