Dielectric Properties Of Rare Earth Doped Barium Titanate

BaTiO₃（BT）is a kind of perovskite structure.It has the characteristics of high dielectric constant,high resistivity,high compressive strength and excellent insulation performance,etc.It is often used to prepare miniature capacitors with small volume and large capacity,as well as grain boundary layer capacitors and PTC thermistors with semiconductor characteristics.Ion substitution doping is an effective way to regulate the electrical properties of piezoelectric ceramics.The photocatalytic properties of barium titanate and the electrical properties of Barium titanate ceramics can be regulated by using appropriate dopants.Rare earth elements doped with barium titanate have become a research hotspot in recent years due to the obvious improvement of dielectric properties.According to a large number of reports,doping rare earth elements as additives,peak-spreading agent,peak-shifting agent,etc.,has a significant effect on the dielectric properties of barium titanate synthesized by different methods.However,the study on dielectric properties of pure barium titanate doped with rare earth oxides by solid phase method still needs to be supplemented and the system improved.In this study,three rare earth oxides Y₂O₃,La₂O₃and Sm₂O₃were doped into pure grade barium titanate by solid-state reaction,and barium titanate ceramic samples with relatively stable dielectric constant and low dielectric loss were prepared.It has broad application prospect in high fidelity signal transmission device and long service life device.This study is divided into the following three parts.（1）Y,La and Sm doped BTx R powder BTx R（x=2～10,R represents rare earth elements）was prepared by labring-annealing process.The doped barium titanate powder after pre-firing was heated at 4℃/min by solid phase method and kept at 1275℃for 2 hours.Then,rare earth elements doped Barium titanate ceramic sheets were sintered at high temperature.After 150℃silver plating and curing,the samples with measurable dielectric constant and dielectric loss were obtained.（2）X-ray Diffraction（XRD）,Scanning Electron Microscopy（SEM）and Energy Dispersive Spectroscopy（EDS）were used for characterization.The preparation of rare earth doped Barium titanate powder was characterized,and no second phase was shown in the XRD pattern.A small amount of doped BT2Y,BT2L and BT4S had better crystallization degree.With the increase of doping amount,the peak value showed a slight shift to the right.SEM images showed that the grain diameter did not change significantly,ranging from 0.4 to0.9μm,but La,Sm doped barium titanate powder showed slight agglomeration.EDS can detect doped elements in all three kinds of doped barium titanate.Three kinds of rare earth doped barium titanate ceramics were characterized.XRD patterns showed that the rare earth doped Barium titanate ceramics sintered were all pure barium titanate ceramics without heterogenous peaks.With the introduction of doping elements,the peak value of doped Barium titanate shifted slightly to the left compared with pure Barium titanate.Compared with pure barium titanate,the lattice constants of doped Barium titanate mostly increased slightly,and the doped Barium titanate tetragonal phase did not show obvious enhancement.The SEM spectra showed that the distance between grains of doped ceramic sheets increased,and the introduction of rare earth ions led to the appearance of pore defects in ceramic samples,with the grain diameter of about 0.5～1.2μm.With the increase of Y element,the growth of grain was significantly inhibited,and the pores of La doped barium titanate ceramic sheets were more.Doping elements can be detected in EDS.Compared with pure barium titanate ceramic,the density of rare earth doped barium titanate ceramic sheet decreases and the volume increases.（3）Sample grouping test dielectric properties.At 1KHz,three rare earth doped barium titanate and pure Barium titanate silver plated ceramics were divided into four groups for testing.According to the measurement,the dielectric loss of rare earth doped Barium titanate ceramic wafer decreases greatly in all frequency bands compared with pure barium titanate ceramic wafer.Among them,the dielectric loss of low-frequency,Y-doped Barium titanate ceramic wafer,BT2S,BT4S and BT10S shows excellent performance and is all less than0.025.The dielectric loss of La doped Barium titanate ceramic sheet and BT6S is lower than0.02.This is because trivalent rare earth ions replace the B site and play the role of electron acceptor to neutralize the oxygen vacancy donor to prevent Ti⁴⁺reduction.After that,A small amount of trivalent rare earth ions enter the A site,which maintains the electric neutrality of the lattice to a certain extent and further reduces the high frequency dielectric loss.In terms of dielectric constants,the dielectric constants of barium titanate ceramic plates doped with three rare earth elements decreased somewhat but the stability was relatively good.The dielectric constants of La doped Barium titanate ceramic plates were the lowest and distributed in100-400.These phenomena are explained by lattice defects,spontaneous polarization and substitution doping.