Study On Dielectric Properties And Defect Chemistry Of (Ba_1-xLa_x)(Ti_1-xLu_x)O₃ Ceramics

Barium titanate（BaTiO₃）is a simple compound,which is the most widely used material in the electronic ceramics industry with a room temperature permittivity of up to 1600,known as the “pillar of the electronic ceramics industry”.It was reported for rare-earth-doped BaTiO₃ that with the contraction of ionic size of lanthanide ions,the site occupations of rare-earth ions in BaTiO₃ gradually shift from the Ba sites to the Ba/Ti double sites simultaneously to the Ti sites.The double rare-earth doping can effectively reduce the dielectric loss（tan δ）and improve the dielectric permittivity（ε’）of BaTiO₃ ceramics.The dielectric response tranfers from first-order phase transition（FPT）into diffuse phase transition（DPT）.Lu³⁺(4f¹⁴)is a smallest rare-earth ion in lanthanides.It was reported that Lu is prone to occupy the Ti site in BaTiO₃.In this work,Lu-doped BaTiO₃ ceramics,La/Lu and Dy/Lu co-doped BaTiO₃ ceramics were prepared at 1400 °C/12 h using cold-pressed ceramic preparation technology.X-ray diffraction（XRD）,Raman spectroscopy,electron paramagnetic resonance（EPR）,scanning electron microscopy（SEM）and dielectric-temperature characteristics were measured to investigate the solid solubility,crystal structure,site occupations,spectral properties,dielectric properties,and defect chemistry.The main results are as follows:1.The nominal(Ba_1-xLu_x)Ti_1-x/4O₃（x = 0.01）ceramic（BLT）has a single-phase tetragonal structure,with an average grain size of 0.7 μm.The solid solubility of Lu in the BaTiO₃ lattice is very low（x = 0.01）.Lu³⁺ is prone to occupy the Ba site in the BaTiO₃ lattice.A self-compensation mode and O vacancy defects cannot be formed.Two EPR signals can be detected.The signals at g = 1.974 and g = 2.004 are associated with Ba vacancies and Ti ones,respectively.The dielectric peak of BaTiO₃ shifts to lower temperature at a shifting rate of-9 °C% Lu³⁺.BLT exhibits a high volume resistivity（ρ > 2.5 × 107 ?cm）and a low dielectric loss（tan δ < 0.05）below 110 °C,which reveals that the cation-vacancy compensation is dominant when Lu³⁺ occupis the Ba site in BaTiO₃,and the electronic compensation cannot be induced.The single-phase BLT ceramic with x = 0.01 satisfies the Y5 V dielectric specification.2.The solid solubility of nominal（Ba1-x Lax）（Ti1-xLux）O3 ceramics（BLaTLu）is x = 0.05,which indicates that the co-doping with La and Lu in BaTiO₃ can improve the solid solubility of Lu in the Ti site.During the sintering process,La³⁺ and Lu³⁺ ions enter the Ba sites and the Ti sites,respectively,forming La_Ba-Lu_Ti defect complexes,i.e.a self-compensation（donor-acceptor）mode.Moreover,a small number of Lu³⁺ ions are incorporated into the Ba sites to induce Ti vacancies（Ti""_V）.Lu³⁺ shows a weaker amphoteric behavior.The co-doping with La and Lu can suppress the grain growth of BaTiO₃ ceramics,forming a fine-grained ceramic with an average grain size of GS = 0.9 1.0 μm.The relative density of BLaTLu decreases rapidly from 83 % to 72 %.Two signals at g = 1.974 and g = 2.004 are associated with Ba vacancies（VBa）and Ti ones（VTi）,respectively,which originate from electron trapping in two kinds of intrinsic cation point defects.A Mn²⁺ sixtet signal is attributed to Mn impurities in ceramics.A rare signal at g = 2.2 is discussed associating with impurities in the initial materials.3.The BLaTLu ceramic with x = 0.05 satisfies the Y5 S dielectric specification,with a room-temperature dielectric permittivity of ε’RT = ¹800.This ceramic exhibits the lowest dielectric loss（tan δ = 0.01）,which is attributed to a nearly complete self-compensation mode of La_Ba-Lu_Ti.4.(Ba_1-xDy_x)(Ti_1-xLu_x)O₃ ceramics have a low solid solubility（x < 0.03）and it is not easy to form Dy_Ba-Lu_Ti defect complexes.However,the ceramic with x = 0.03 satisfies the Y5 T dielectric specification and exhibits a lower dielectric loss of tan δ = 0.019 at room temperature.