Papers by Author: Xiang Yun Deng

Abstract: Bulk dense nanocrystalline BaTiO3 ceramics ranging from 15 nm to 100 nm have been successfully prepared by the spark plasma sintering method. Raman spectra and X-ray diffraction were used in combination with electron microscopy to study the evolution of lattice structure and phase transformation behavior with grain growth from nanoscale to micrometre scale for BaTiO3 ceramics. Scanning nonlinear dielectric microscopy measurements revealed temperature-dependent variations in contrast, which were attributed to domain rearrangements in BaTiO3 ceramics below 100 nm. Furthermore the piezoresponse hysteresis loops showed that the nanocrystalline BaTiO3 ceramics were switchable and ferroelectricity was retained at the high temperature of 290 oC, demonstrating the existence of nano ferroelectric domains and the ferroelectric phase still retained above Curie temperature, which confirmed the diffused phase transition character in nanograin BaTiO3 ceramics. The dielectric data also show a ferroelectric to paraelectric phase transition in nanograin BaTiO3 ceramics.

Abstract: The full potential linearized augmented plane wave method within the generalized gradient approximation was used to calculate electronic structure of nanocrystalline BaTiO3 ceramics. We calculated the total and partial density of states of 50 nm BaTiO3 ceramics. The results show that the atoms distribution of nanograin BaTiO3 ceramics is different from those of coarse BaTiO3 ceramics. It is also revealed that the hybridization between Ti 3d and O 2p is very strong, which is very important to the ferroelectric stability of nanocrystalline BaTiO3 ceramics.

Abstract: SrBi2Nb2O9 (SBN) with different Bi2O3 contents were prepared by solid-state reaction method and then spark plasma sintering. The Influence of Bi2O3 on the properties of SBN was studied. The results showed that the increased Bi2O3 contents can enhance densification and improve the dielectric properties. This might have close relation to the low melting point of Bi2O3 and special sintering way of SPS, which usually results in some change in micro-structure.