Study On The Relaxation Behavior Of BaTiO₃ Ceramics Modified With BiMO₃?M=Y,Fe,Al?

Relaxor ferroelectrics have attracted much interest owing to the rich diversity of their structural and physical properties,and have been extensively used for the Multilayer Ceramic Capacitor?MLCC?application.The distinctive properties of classical relaxor dielectrics are broad,frequency-dependent peaks in plots of relative permittivity versus temperature,and strong frequency dispersion in dielectric loss tangent.Barium titanate?BaTiO₃?is a ferroelectric compound with the perovskite type structure and interesting electrical properties: ferroelectricity,high dielectric constant,piezoelectricity,and pyroelectricity.Historically,it is widely used in piezoelectric sensors,actuators,low temperature cofired ceramics?LTCCs?,multilayer ceramic capacitors?MLCC?and electro-optic devices with some additives.Additives are choosen specifically for their sintering functions and dielectric properties.A crossover to the relaxor state is observed in BaTi O₃ by both heterovalent and isovalent ionic substitutions.The relaxor behavior is induced by substitutions either on A-or B-or on both A-and B-sites of the perovskite lattice ABO₃.Bi-based perovskites are the prominent systems in this regard.In this work,we prepare the BT powder with solid state reaction method.Additives BiMO₃?Y,Fe,Al?are choosen to modify the proerties of BT ceramics,and the crystal structure,microstructure,dielectric and ferroelectric properties of the BT-based ceramic were investigated systematically.?1?The polycrystalline?1-x?BaTiO_3-xBiYO₃??1-x?BT-x BY??x=0.00⁰.30?ceramics were fabricated via a conventional solid state reaction method.It was investigated for compositions,X-ray powder diffraction patterns indicated tetragonal symmetry at x?0.04,whilst the XRD patterns for x>0.04 were pseudocubic.A progressive decline in ?rmax with the elevation of x leads to near temperature-stable dielectric properties over a wide temperature range.For x?0.04,dielectric measurements indicated relaxor behavior.The increasing amount of BY content improved the dielectric temperature stability of BT ceramics effectively.It was found that x=0.30 can meet the X9 R criterion,with ??/??25?±15% in the temperature range of-55-200 oC.?2??1-x?BaTiO_3-x BiFeO₃??1-x?BT-x BF??x=0⁰.08?ceramics are synthesized via the conventional solid state method.And the influences of BF on the crystal structure,micromorphology and dielectric properties of BT ceramics have been investigated.X-ray diffractometer?XRD?and Raman spectra demonstrate a systematically structural transition from tetragonal to pseudo-cubic phase occurs from 0?x?0.08.The grain size of the samples becomes smaller and more uniform with the elevation of x.Dielectric behaviors display that the samples with x=0,0.06,and 0.08 belong to normal ferroelectric,diffused ferroelectric,and relaxor ferroelectric,respectively.High frequency independent conductivity arises for x=0.06 and x=0.08 due to the mobility of O2-ions and the defects generated in grain and grain boundary,which is in association with hopping of charge carriers along the Fe²⁺-oV-Fe³⁺chain and between Fe²⁺ and Fe³⁺ions,respectively,indicate different hopping process for electrons.The polarization-electric loops become narrow,demonstrate that there are the paraelectric and cubic phase exist in the ceramics,which is in agreement with the XRD patterns and Raman spectra of the BT-BF ceramics.?3?The polycrystalline?1-x?BaTiO_3-x BiAlO₃??1-x?BT-x BA??x=0⁰.15?ceramics are fabricated via a conventional solid state reaction method.X-ray diffraction and Raman results show a structural evolution from a tetragonal phase to a cubic one with increasing x.Dielectric studies exhibit a diffuse phase transition characterized by a strong temperature and frequency dispersion of permittivity.The dielectric maxima temperature Tm decrease,due to the strong interaction of Bi³⁺ and Al³⁺ with Ba²⁺ and Ti⁴⁺.?1-x?BT-x BA ceramics underwent a ferroelectric to relaxor transition at x=0.06.Activation energy with dozens meV is obtained using the Vogel-Fulcher relationship,which is attributed to thermally activated off-center ion hopping.Raman spectra of the?1-x?BT-x BA ceramics at 264 cm-1,the paraelectric and cubic phase exist in the ceramics,so the polarization-electric plots are in the form of narrow ellipsoids with the elevation of x.Meanwhile,the discharged energy density of 0.85 BT-0.15 BA is 0.16 J/cm3.