铁酸铋基陶瓷的相结构调控及高温压电性能优化OA

Introduction In this paper,0.99(0.7BiFeO3-0.3BaTiO3)-0.01Bi0.5Na0.5TiO3-xLi2CO3(i.e.,x=0,0.001,0.003,0.005;abbreviated as 0Li,0.1Li,0.3Li,0.5Li,BFBTBNT-xLi)ceramics were prepared by a conventional sintering technique.The ceramics gradually changed from the R phase to PC phase structures,and the ceramic with 0.3Li showed obvious coexistences of R and PC phases as the addition of Li2CO3 increases.The Curie temperature of Li2CO3-doped BFBTBNT-xLi ceramics increases from 483℃to 535℃,and the dielectric loss of the samples decreased.The remanent polarization of the ceramics increased with increasing the Li2CO3 addition,reaching the maximum value at 0.3Li.Subsequently,the polarization decreased due to the increased coercive field.Li2CO3 could enhance the insulation of the ceramics because of the enhanced migration barrier of oxygen vacancies.The ceramic with 0.3Li could be obtained with an optimal piezoelectric constant of 183 pC·N-1 and a high depolarization temperature of 380℃.This material displayed a great potential in high-temperature piezoelectric application. Methods The 0.99(0.7BiFeO3-0.3BaTiO3)-0.01Bi0.5Na0.5TiO3-xLi2CO3+1%MnO2(x=0,0.001,0.003,0.005;abbreviated as 0Li,0.1Li,0.3Li,0.5Li,BFBTBNT-xLi)ceramics were prepared by a conventional sintering process.The raw materials were weighed according to the stoichiometric ratio and ground for 12 h.After grinding,the ground raw materials were firstly sintered at 720℃for 5 h,and then the mixtures with MnO2 were further ground for 12 h.After granulating and pressing,the samples were heated at 600℃for 10 h.Afterwards,the samples were heated at 1000℃for 3 h. The phase structure of the ceramics was analyzed by X-ray diffraction(XRD,Bruker Co.,Germany).The microstructures of the ceramics were determined by scanning electron microscopy(SEM,JSM Co.,Japan).In order to test the electrical properties of the BFBTBNT-xLi ceramics,the silver paste was coated on the surface of the samples and fired at 800℃for 10 min to form silver electrodes.Afterwards,the dielectric constant and loss as a function of temperature and impedance spectroscopy was determined by impedance analysis(Agilent E4980A).The ferroelectric performance and J-E curves was measured by ferroelectric analysis(Precision Premier II,Radiant Co.,USA).The chemical binding state of O was tested by X-ray photoelectron spectroscopy(XPS,PHI Co.,USA).The electron paramagnetic resonance measurements were performed by the EPR spectroscopy(EPR,Bruker Co.,Germany).The d33 values at room temperature were measured by a quasi-static piezoelectric constant apparatus(ZJ-3A,China).The in-situ d33 values were collected by a quasi-static d33 apparatus(YE2730A,Sinocera Co.,China). Results and discussion The content of the R phase continuously decreased with increasing Li2CO3 addition,especially in the sample with 0.3Li.The content of the R phase reduced to 36.28%,which was the MPB.The content of the R phase in the sample with 0.5Li further decreased to 18.76%,while the content of the PC phase increased to 81.24%,indicating that the sample is mainly composed of the PC phase.The microstructure showed that the surface of the sample was smooth without obvious holes,and the ceramic grains were full and the grain boundaries were clear.The addition of Li2CO3 could refine the grains,which was beneficial to improving the toughness against breakdown.The Curie temperatures(TC)of the samples with 0Li,0.1Li,0.3Li and 0.5Li were 483,502,521℃and 535℃,respectively.The dielectric loss of the BFBTBNT-x Li showd a significant increase with increasing temperature,especially when the temperature exceeded 150℃.The dielectric loss of the ceramic samples modified by Li2CO3 was significantly reduced,especially more significantly in the high-temperature environment.The residual polarization of the ceramics with the addition of Li2CO3 increased,reaching a peak value for the ceramic with 0.3Li.The samples exhibited semi-circular complex impedance characteristics,and the resistance of the ceramics decreased with increasing temperature,which was in line with the characteristics of the semiconductor conduction mechanism.The activation energies(Ea)of the ceramics with 0Li,0.1Li,0.3Li and 0.5Li were 1.196,1.218,1.251 eV and 1.263 eV,respectively.The oxygen vacancies were inhibited with the gradual addition of Li2CO3,thereby enhancing the insulating properties of the ceramics.The leakage current of the samples with 0.1Li,0.3Li and 0.5Li modified by Li2CO3 was improved;especially the leakage current of the sample with 0.5Li reduces to 10-6 A·cm-2,which was reduced by two orders of magnitude.The d33 values of the ceramics with 0Li,0.1Li,0.3Li and 0.5Li were 149,161,183 pC·N-1 and 152 pC·N-1,respectively,showing a consistent with the residual polarization.The ceramic with 0.3Li exhibited the maximum piezoelectric constant because of the higher residual polarization,fewer oxygen vacancies and leakage current,thus enabling a more complete polarization and demonstrating the optimum piezoelectric performance.The ceramics modified by Li2CO3 showed a high-temperature stability,and the de-polarization temperatures(Td)of the ceramics with 0Li,0.1Li,0.3Li and 0.5Li were 350,370,380℃and 390℃,respectively. Conclusions The 0.99(0.7BiFeO3-0.3BaTiO3)-0.01Bi0.5Na0.5TiO3-xLi2CO3(x=0,0.001,0.003,0.005;abbreviated as 0Li,0.1Li,0.3Li,0.5Li)ceramics were prepared by a conventional sintering process.The ceramics gradually changed from the R to PC phase structure as the addition of Li2CO3 increased.The ceramic with 0.3Li showed obvious coexistences of the R and PC phases.The content of R phase in the ceramics BFBTBNT-x Li decreased from 78.02%to 18.76%,while the content of PC phase increased from 21.98%to 81.24%.The addition of Li2CO3 could refine the grains,which was beneficial to improving the toughness against breakdown.The Curie temperature increased in the ceramics BFBTBNT-xLi doped with Li2CO3,and the dielectric loss of the ceramics was significantly reduced,especially at high temperatures.The remanent polarization of the ceramics increased gradually with increasing the Li2CO3 addition,reaching the maximum value for the ceramic with 0.3Li.The oxygen vacancies in the ceramics were suppressed as the Li2CO3 addition increased,thus enhancing the insulation performances.The piezoelectric constant of the ceramic with 0.3Li was 183 pC·N-1,and the depolarization temperature was as high as 380℃,which could be promising for high-temperature piezoelectric applications.