The Doping Modification And Aging Properties Of Barium Bismuth Layered Ceramics Bismuth Titanate Barium And Bismuth Niobate Barium

In this thesis, the lanthanum and scandium substitution was carried out in some typical bismuth layer-structured compounds and the variation of microstructure and dielectric, ferroelectric and aging properties were firstly systematically investigated. And then the relation between the structure stability and the average radius of A-site cations was discussed. Finally, some other rare earth (yttrium, neodymium) substitution of some Ba-based bismuth layer-structured compounds were also described and analyzed.With the La3+doping, the room temperature relative permittivity of the BaBi4Ti4O15samples is increased, and dielectric loss is decreased. For the Ba(Bi1xLax)4Ti4O15(BBiLxT) phase, only a weak variation with respect to the F2mm space group can be suggested from single crystal X-ray diffraction. The microstructure confirms the samples have a well-proportioned grain size and a higher density. The substitution also results in a marked improvement in the remnant polarization. The doping of La’ in BBiLxT ceramics increased the room temperature relative permittivity aging properties.Similar results were obtained in Sc3+substituted BaBi4Ti4O15. With increasing Sc3+substitution, the pyrochlore phase content of the samples was significantly reduced. And when the amount of Sc3+doping was lat%, the crystal structures of the samples were almost pure perovskite structure. Compared with La3+doping, the SC3+substitution made the BaBi4Ti4O15ceramics much more denser. The substitution also results in a marked improvement in the aging properties. But the La3+substitution have little effect on the dielectric and ferroelectric properties of the samples.The author suggested that, according to the microstructure analysis, there may be two reasons lead to the above phenomenon:firstly, Doping La3-/Sc3+could compensate for the Bi-omission caused by Bi2O3volatilized, will help to improve the density and to reduce the dielectric loss of the ceramics. In addition, the dielectric constant of the samples can be improved by doping La3+or Sc3-. because each of the La-O and Sc-O’s bond energy is larger than Bi-O makes the samples more stable.In order to further clear the relationship between the factors contributing to the ferro-electricity in bismuth layer-structured compounds, La3+/Sc3-/Y3+/Nd3+were used to replace Bi3+in BaBi2Nb2O9ceramics. With the Sc3+doping, the samples have a well-proportioned grain size and a higher density.And the grain morphology obvious is plate-shaped, which is due to the bismuth layered compound has a layered structure. The substitution also results in a marked improvement in the dielectric properties. Doping La3+and Y3+were also conducive to the formation of the ceramic tetragonal phase and the layered structure. However, large Nd3+was used to replace Bi3+in BaBi2Nb2O9can not effectively suppressed by the Bi2O3volatile vacancies in the high-temperature sintering.This may be duo to the the density of the samples was reduced, because of the presence of pores the in the ceramics is due to the Bi-Vacancies exist. For the dielectric properties, with the rare earth ions doping, the trend of the relative room temperature dielectric constant became more complex. This may be duo to the layered-structure and niobate tungsten bronze structure exist were existed in BBN ceramics.The specific mechanism is needed for research and exploration.