Study On High-dense Perovskite Electronic Ceramics Co-doped With Multi Rare-earth

In this work,we prepared Ba Ce O₃ co-doped with Tb、Sr,and Ba Ti O₃ co-doped with Tb、Ce and Dy、Tb、Ce using the mixed-oxides method.X-ray diffraction（XRD）,scanning electron microscopy（SEM）,energy-dispersive X-ray spectroscopy（EDX）,X-ray photoelectron spectroscopy（XPS）,Raman spectroscopy（RS）,electron paramagnetic resonance（EPR）,and dielectric measurements were employed to investigate the solid solution,structure,morphologies of the ceramics,the valence states of the elemaents,the site occupations of the ions and the defact chemistry.The dielectric materials satisfying X9V,X8U,Z4T and X4S specifications were successfully achieved.The main contents listed as following:（1）The single phase ceramics(Ba_3-xSr_x)(Tb_3-xCe_x)O₉（x=1 and 1.5,abbreviated as BSTC1and BSTC3/2）were prepared at 1400°C.BSTC1 presents a trigonal perovskite structure and BSTC3/2 presents an orthorhombic perovskite structure.The relative density of BSTCs is about93%and the grain size distributes from 0.2 to 3μm.Ba/Sr ions at the A-sites and Ce/Tb ions at the B-sites in the perovskite lattice are randomly disordered and exhibit homogeneous concentration distributions.The EPR,XPS,and electrical results confirm that Ce exists as Ce⁴⁺and Tb exists as Tb⁴⁺and Tb³⁺in BSTCs,respectively.The existence of oxygen vacancies and possible local ording still need to be further explored.At room temperature two BSTC ceramics exhibit a similar semiconducting behavior and the difference in x had little effect on theirσ–T relations.The electrical conductivity changes rapidly with the variation of temperature and the room-temperature-conductivity changes slowly with the variation of frequency.（2）Nominal(Ba_1-xTb_x)(Ti_1-5x/4Ce_x)O₃（BTTC）ceramics are sintered at 1400°C for 12 h in air and the solid solubility of Ce in BTTC is x<0.02,which suggests that doping Tb at A site can decrease the incorporation of Ce at B site.There was no influence with the solid solubility of Ce at B sites when the sintering temperature was improved to 1450°C.Nominal(Ba_1-xTb_x)(Ti_0.96-5x/4Tb_xCe_0.04)O₃（BTTTC-1）ceramics were prepared at 1450°C with a solid solubility of x>0.04.（3）The(Ba_1-xTb_x)(Ti_0.96-xTb_xCe_0.04)O₃（BTTTC）ceramics prepared at 1450°C possess a higher solid solubility（x=0.05）,and BT4TTC exhibits a good compactness with a relative desity about 91.4%.At room-temperature,BT1TTC presents a tetragonal structure and the others present a cubic structure.The EPR results suggest that Ce occupies Ti site as Ce⁴⁺and Tb occupies Ti and Ba sites as Tb⁴⁺and Tb³⁺,respectively,at a low doped level;with the increase of the dopent content,Ce occupies Ti and Ba site as Ce⁴⁺and Ce³⁺,respectively,and most of the Tb occupies Ti site as Tb⁴⁺.The dielectric measurement result suggests that with the increase of the dopent content the T_c decreases at a rate of 16°C/at.%,and the dielectric loss of all the samples is greater than 0.04.BT5TTC satisfy X9V(-82%≤(ε’-ε_RT’)/ε_RT’≤22%)dielectric index.The Tc appears at around 62°C,and the maximum dielectric constant isε_max’=3104,and the corresponding dielectric loss is tanδ=0.08.（4）The ceramics with nominal formula(Ba_1-xDy_x)(Ti_1-5x/4Ce_x/3Tb_2x/3)O₃（x=0.01～0.12,BDTCT1～12）were prepared at 1400°C and the solid solubility is x=0.07 which is the same with the salf-compensation mode Dy-doped Ba Ti O₃,(Ba_1-xDy_x)(Ti_1-xDy_x)O₃.This phenomenon shows that the doping of Tb and Ce at B sites does not affect the formation of self-compensation mode of Dy.The relative density of BDTCT4 and BDTCT7 is 90.8%and 91.5%,respectively.When x=0.01～0.03,the T_c decreases at a rate of 3°C/at.%,and when x=0.04～0.07,the T_cdecreases at a rate of 23°C/at.%.When x=0.03,the dielectric constant（ε’=2800）in the range of-55～65°C is almost not affected by temperature,which satisfies the dielectric index of X4S(-22%≤(ε’-ε_RT’)/ε_RT’≤22%).When x=0.04,in the range of-55～65°C the sample satisfies the dielectric index of Z4T(-33%≤(ε’-ε_RT’)/ε_RT’≤22%),and the dielectric loss is tanδ<0.02.When x=0.07,in the range of-55～150°C,the dielectric loss tanδis less than 0.04,which satisfies the dielectric index of X8U(-56%≤(ε’-ε_RT’)/ε_RT’≤22%).