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

Barium titanate?BaTiO₃?is a common environment-friendly dielectric material,known as“pillar of electronic ceramics industry”.The structural modification of rare-earth dopants on BaTiO₃ ceramics is an effective way to obtain dielectric ceramics with superior comprehensive performance.In this work,the dielectric properties and defect chemistry of light rare earth/calcium co-doped BaTiO₃ ceramics were strudied,including Nd³⁺singly and doubly doped BaTiO₃ ceramics,Pr doped BaTiO₃ ceramics,and light rare earth?LRE=La,Pr,Nd,Sm?/calcium co-doped BaTiO₃ ceramics,which were prepared using the solid-state reaction method.The structure,microstructure,solid solubility,valence states,dielectric properties,site occupation,and point defect chemistry were investigated using X-ray diffraction?XRD?,scanning electron microscopy?SEM?,dielectric-temperature characteristic?DTC?,electron paramagnetic resonance?EPR?,Raman spectroscopy?RS?,and photoluminescence?PL?.The results are as follows:1.Defect chemistry and low-loss behavior of Nd-doped BaTiO₃ ceramic(Ba_1–xNd_x)Ti_1–x/4O₃?BNT?exhibited a tetragonal perovskite structure at x?0.04 and a pseudo-cubic perovskite structure at x?0.05.BNT with x=0.03 and x?0.05 are semiconductors because of the strong doping effect from A-site Nd³⁺.An abnormal phenomenon is that BNT with x=0.04?BN4T?was a common ferroelectric,which showed higher room-temperature permittivity(??_RT=6955)and lower dielectric loss?tan?<0.05?over the temperature range-50 to 150°C.The point defect chemistry of BNT was given.The higher concentrations of Ti vacancies,the intense reduction from Mn³⁺or Mn⁴⁺to Mn²⁺,and a small amount of Ba vacancies were responsible for lower dielectric loss in BN4T.2.Aging-resistant behavior and room temperature electron spin resonance of Nd³⁺in singly and doubly doped BaTiO₃ ceramics associated with preservation historyAfter they had been preserved over a long period of time,(Ba_0.96Nd_0.04)Ti_0.99O₃?BN4T?with a tetragonal structure and(Ba_0.96Nd_0.04)(Ti_0.94Ce_0.05)O₃?BN4TC5?ceramics with a pseudo-cubic structure exhibited a broader EPR signal at g=2.338 and a narrow EPR signal at g=2.151 at RT,respectively,which are most likely originated from Nd³⁺Kramers ions in BN4T and a Nd³⁺–Ce⁴⁺defect complex in BN4TC5.The Raman scattering investigations provided evidence that some rhombohedral distortions formed owing to long-term preservation of the two samples could not be detected by XRD at room temperature.Thermal treatment gave rise to the disappearance of both rhombohedral distortions and Nd³⁺-related EPR signals.This finding will have far-reaching implications for RT-accessible realization of low-temperature detection methods.For BN4TC5 stored for 11 years,a slight decrease in permittivity maximum???_m?and a slower shift in dielectric-peak temperature?T_m?relate to the slightly expanded lattice and its rhombohedral distortion caused by long-term preservation.The oxidation of Mn impurities with time is responsible for a slight increase in tan?at RT.As a whole,BN4TC5 is considered to be a better aging-resistant dielectric.3.Study on solid solubility and site occupations in(Ba_1-xPr_x)Ti_1-x/4O₃ ceramicsThe solid solubility and site occupations of Pr ions in(Ba_1-xPr_x)Ti_1-x/4O₃?BPT?were investigated using both X-ray diffraction?XRD?and electron paramagnetic resonance?EPR?techniques.The results indicated that the solubility limit was x=0.17 and BPT with 0.10?x?0.17 exhibited a single-phase cubic perovskite structure.Pr ions were substituted predominantly for Ba-sites.4.Crystal structure,solid solution and dielectric properties of(Ba_1–xLRE_x)(Ti_1–x/2Ca_x/2)O₃?LRE=La,Pr,Nd,Sm?ceramicsThe solubility limits of La?Pr?Nd?Sm in(Ba_1–xLRE_x)(Ti_1–x/2Ca_x/2)O₃?BRTCa?were determined by XRD to be 0.54,0.35,0.29,and 0.35,respectively.The change in unit-cell volume?V₀?with x for Pr/Ca and Nd/Ca co-doped BaTiO₃ ceramics roughly followed Vegard's law.However,an abnormal Vegard's law was discovered for La/Ca co-doped BaTiO₃ ceramics.This abnormal Vegard's law was simulated and the V₀-x relation was expressed by y=7.63x+62.489.The permittivity maximum of BPTCa with x=0.03 was?'_m=1309 and this sample exhibited a lower dielectric loss of tan?=0.013.