| Bismuth-based layered perovskite ferroelectric materials have attracted wide attention due to their potential applications in non-volatile random storage devices.Among these ferroelectric materials,bismuth titanate(Bi4Ti3O12,BTO)is considered to be a promising candidate because of its large spontaneous polarization?Ps=4050?C/cm2?.The insertion of magnetic groups into bismuth titanate matrix can make the material ferroelectric and ferromagnetic at the same time,which is one of the effective ways to obtain room temperature multiferrous materials.Bi4Ti3O12 based multiferroic ceramics were prepared by sol-gel process and sintered by means of sintering and hot pressing respectively.The ferroelectric,dielectric and magnetic properties of ceramics were also discussed.The main results are as follows:1.Bi4Ti3O12-nLaFeO3?n=0.5,1,1.5?multiferrous ceramics were prepared by normal pressure and hot pressing sintering respectively.TEM observation confirmed that LaFeO3 magnetic unit was successfully inserted into Bi4Ti3O12 ferroelectric matrix.Ferroelectric measurements show that the residual polarization and coercive field of ceramics increase with the increase of LaFeO3 layer number n.Compared with the ceramics sintered at atmospheric pressure,the breakdown electric field,ferroelectric properties,dielectric properties and magnetic properties of the ceramics sintered by hot pressing are obviously enhanced.For Bi4Ti3O12-nLaFeO3 ceramics prepared by two sintering methods,the magnetization of Bi4Ti3O12-0.5LaFeO3ceramics is the highest.2.Bi3.15Nd0.85Ti3O12-BiFeO3(LaFeO3,LaCo0.5Fe0.5O3)multiferrous ceramics were prepared by hot pressing sintering.The results of X-ray diffraction show that BNdT-?BFO,LFO?is pure phase,and there are second phase peaks at the diffraction angles of 31.7°and 39°in the diffraction pattern of BNdT-LFCO.Scanning electron microscopy?SEM?results show that the ceramics have high density,no obvious stomata,and are composed of randomly oriented flake grains.The thickness of flake grains is mainly 0.1-0.2?m.Among them,the grain thickness of BNdT-BFO ceramics is larger than that of BNdT-LFO?LFCO?.Ferroelectric measurements show that the residual polarization values of BNdT-BFO?LFO,LFCO?ceramics are 1.98,1.17 and 0.31?C/cm2,respectively.The leakage current densities of BNdT-?BFO,LFO,LFCO?ceramics are 3.47×10-66 A/cm2,1.63×10-55 A/cm2and 1.75×10-66 A/cm2respectively when the electric field strength is 150 kV/cm.The dielectric properties of BNdT-BFO?LFO,LFCO?ceramics show that the dielectric constants are 212.2,238.2 and 111.5,and the dielectric losses are 0.0088,0.0073 and 0.0098,respectively.The room temperature magnetic measurements confirmed that BNdT-?BFO,LFO,LFCO?ceramics exhibited obvious room temperature magnetism with saturation magnetization of 0.004 emu/g,0.0042 emu/g and 0.8096 emu/g,respectively.For BNdT-LFCO ceramics,the saturation magnetization of BNdT-LFCO ceramics increases abnormally at room temperature due to the existence of second-phase magnetic oxides.3.BLT-?BFO,LFO,LFCO?multiferrous ceramics were prepared by hot pressing sintering.X-ray diffraction results show that BLT-?BFO,LFO?is pure phase,and there are second phase peaks at the diffraction angles of 31.7°and 39°in the diffraction pattern of BNdT-LFCO.Scanning electron microscopy?SEM?results show that the ceramics are highly dense and consist of randomly oriented lamellar grains with a thickness of mainly 0.1-0.2?m.Ferroelectric measurements show that the residual polarization values of BLT-BFO?LFO,LFCO?ceramics are 5.19,5.20and 0.25?C/cm2 at the electric field strength of 200 kV/cm.Under 160 kV/cm electric field,the leakage current densities of BLT-?BFO,LFO,LFCO?ceramics are1.85×10-66 A/cm2,1.46×10-44 A/cm2 and 1.79×10-66 A/cm2,respectively.The dielectric properties of BLT-?BFO,LFO,LFCO?ceramics were measured at 100 kHz.The dielectric constants were 206.6,228.7 and 188.7,and the dielectric losses were 0.0117,0.0141 and 0.0065,respectively.Room temperature magnetic measurements confirm that BLT-?BFO,LFO,LFCO?ceramics exhibit obvious room temperature magnetism with saturation magnetization of 0.0104 emu/g,0.0097 emu/g and 0.7258 emu/g under 10 kOe magnetic field,respectively.The saturation magnetization of BLT-LFCO ceramics increases abnormally due to the existence of second phase magnetic oxides. |
PDF Full Text Request