Study On Dielectric Properties And Defect Chemistry Of Ho And Light Rare Earth Co-doped BaTiO₃ Ceramics

(Ba_1-xHo_x)Ti_1-x/4O₃ ceramics and different series of(Ba_1-xR_x)(Ti_1-xHo_x)O₃?R=La,Pr,Nd,Sm,Eu,Gd?ceramics were prepared at a sintering temperature of 1400°C using a solid-state reaction method.The structure,microstructure,solid solubility,point defects,site occupations,defect chemistry,and dielectric properties of these ceramics were studied systematically by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,electron paramagnetic resonance?EPR?,Raman spectroscopy,photoluminescence?PL?,and dielectric measurements.Ho³⁺ions in these ceramics exhibited an amphoteric behavior of the occupations of both Ba-sites and Ti-sites.The significient innovation is that a quantitative estimation method for the occupations of the Ba-sites by Ho³⁺ions in the Ba TiO₃ lattice was established.1.Photoluminescence associated with the site occupations of Ho³⁺ions in Ba TiO₃For BHT1 ceramic with a nominal formula(Ba_1-xHo_x)Ti_1-x/4O₃?x=0.01?,the study on the defect chemistry indicated that Ho³⁺in BHT1 exhibited an amphoteric behavior and the real formula was(Ba_1-xHo_3x/4)(Ti_1-x/4Ho_x/4)O₃?BHTH?.The PL results revealed that under 488-nm laser excitation,the strongest PL band at 564 nm was discovered and verified to arise from the⁵G₆/⁵F₁?⁵I₇ transition of Ho³⁺ions on the Ti-sites in the BaTiO₃ lattice.Upon 532-and 638-nm laser excitations,three PL bands at 545,653,and 755 nm were attributed to ⁵F₄/⁵S₂?⁵I₈,⁵F₅?⁵I₈,and ⁵F₄/⁵S₂?⁵I₇ transitions of Ba-site Ho³⁺ions.The PL effect of Ho³⁺may provide a probe for the site occupations of Ho³⁺ions in widely-used BaTiO₃ dielectric ceramics co-doped with Ho³⁺and other dopants.2.Multiplicity of photoluminescence in Raman spectroscopy and defect chemistry of(Ba_1-xR_x)(Ti_1-xHo_x)O₃?R=La,Pr,Nd,Sm?dielectric ceramics For BRTH ceramics with nominal formulas(Ba_1-xR_x)(Ti_1-xHo_x)O₃?R=La,Pr,Nd,Sm;x?0.04?,the solubility limits in BRTH with R=La,Pr,Nd,Sm were determined by XRD to be x=0.11,0.12,0.06,and 0.14,respectively,and BRTH exhibited pseudo-cubic perovskite structures.The dielectric-peak temperature?T_m?decreased linearly in a certain region at a rate of21°C/at.%La/Ho,–20°C/at.%Pr/Ho,–15°C/at.%Nd/Ho,and–20°C/at.%Sm/Ho,respectively.BRTH with R=La,Pr,Nd,Sm and at x=0.06 satisfied X5 T,X6T,X7 T,and X8 S dielectric specifications,respectively,and they exhibited lower dielectric loss?tan?<0.015?at room temperature.The high-permittivity abnormality for the denser BRTH with R=Sm and at x=0.07 was discovered.Under 532-nm laser,BRTH exhibited the multiplicity of PL in Raman spectra of Nd³⁺/Ho³⁺and Sm³⁺/Ho³⁺.The PL provided the evidence of a small number of Ho³⁺at Ba-site in BRTH and it was determined that the number of Ba-site Ho³⁺ions increased from 0.05 at.%at R=La to 0.19 at.%at R=Sm with increasing atomic number of light rare earth.The defect chemistry in BRTH was given.3.Highly-dense,high-permittivity and low-loss(Ba_1-xGd_x)(Ti_1-xHo_x)O₃ ceramics For BGTH ceramics with nominal formulas(Ba_1-xGd_x)(Ti_1-xHo_x)O₃,the solubility limit was determined by XRD to be x=0.10.BGTH was tetragonal for x?0.05 and pseudo-cubic for x?0.06.BGTH with x=0.07 exhibited high density??_r=95%?,high-permittivity X6 U specification(?'_RT=6980),frequency stability(?(?'-?'_RT)/?'_RT?<7%)over the frequency range of 1 to 10⁶ Hz,and lower dielectric loss?tan?<0.01?over the range of 2 to 3×10³ Hz.Gd³⁺and Ho³⁺in BGTH exhibited an amphoteric behavior.The Ba-site Ho³⁺occupancy rate of the quantitative sample was determined using the PL in the Raman spectra.4.Dielectric properties and photoluminescence of highly-dense(Ba_1-x-x Eu_x)(Ti_1-xHo_x)O₃ceramics For BETH ceramics with nominal formulas(Ba_1-xEu_x)(Ti_1-xHo_x)O₃,the solubility limit was determined by XRD to be x=0.12.BETH was tetragonal for x?0.06 and pseudo-cubic for x?0.07.The dielectric thermal behavior of BETH with x=0.07 exhibited a much broadened diffuse phase transition behavior with X6 U specification and lower room-temperature dielectric loss?tan?<0.015?.The Raman scattering spectra under 532-nm excitation laser showed the multiplicity of PL of Eu³⁺/Ho³⁺.