Papers by Author: Shan Shan Liu

Abstract: Barium-strontium titanate Ba_1-xSr_xTiO₃ [0≤x≤1] has been investigated for tunable microwave application due to their high permittivity, low losses and high tunability. The influence of MgF₂ additives on the dielectric performance of Ba_0.6Sr_0.4TiO₃ (BSTO) were investigated in this paper. MgF₂ doped BSTO ceramics were prepared using the conventional mixed oxide techniques. The phase structure, microstructure and dielectric properties of MgF₂ doped BSTO ceramics were studied. The XRD patterns showed that all the samples exhibit a perovskite phase. A secondary phase of MgO was observed with excessive MgF₂ additives. The grain size of MgF₂ doped BSTO ceramics was slightly increased with the increasing of MgF₂ additives, while the distributed porosity was concentrated to get larger. The relative permittivity, dielectric loss and tunability were decreased accordingly. The relative permittivity was reduced from 3717 (pure Ba_0.6Sr_0.4TiO₃) to 680 (6 wt % MgF₂ doped BSTO), while the tunability changed from 51.7 % to 6.5 %. The dielectric losses were decreased from 0.004 to less than 0.001. The Curie temperature of MgF₂ doped BSTO was first decreased with the additives of MgF₂ (x<2 wt %) then remain the same with the rise of MgF₂ (2≤x≤6) content.

Abstract: Ba_xSr_1-xTiO₃ [(BST), 0£x£1] is a solid solution ferroelectric material exhibiting a large dielectric constant non-linear change with an applied DC electric field. And Ba(Zr_xTi_1-x)O₃ solid solution also has received much attention because of the good tunbality. In this paper, Ba_0.6Sr_0.4(Zr_xTi_1-x)O₃ (x=0.15,0.20,0.25,0.30,) ceramic was obtained by traditional ceramic processing. The structural, surface morphological, dielectric properties, tunable properties of this material as well as the mechanism of their nonlinear dielectric constant under DC electric field were systematically examined. The Zr ions substitution of Ti ions has a strong effect on the grain sizes and the dielectric property. The results show that Ba_0.6Sr_0.4(Zr_xTi_1-x)O₃ (x = 0.2, 0.25,0.3) ceramic is a promising candidate for the DC electric field tunable materials for microwave electronics application, because they exhibit high relative tunability (44%, 48%, 35%, respectively) as the strength of electric field is up to 1.5 kV/mm, and low dielectric loss (0.0026, 0.00044, 0.0015, respectively) at 100 kHz at room temperature. X-ray diffraction analyses indicated that the samples present perovskite phase. Scanning electron microscopy micrograph of sample indicated that the grain size decreased and density increased with Zr concentration increasing.

Abstract: High <001>-textured Na1/2Bi1/2TiO3-BaTiO3 (6mol%BaTiO3) ceramics were fabricated by reactive-templated grain growth (RTGG), using plate-like Bi4Ti3O14 particles prepared by a molten salt method as the templates. The effect of template concentration on the texture development and microstructure evolution was studied, and the mechanisms of grain orientation and densification were also discussed. The design of Bi element reaction has important impact on the texture development.

Abstract: Lead-free Na1/2Bi1/2TiO3-6BaTiO3 (BNT-6BT) ceramics with different dopants were prepared by a conventional ceramic fabrication technique. The influence of doping CeO2, La2O3, Nb2O5 and Co2O3 on the structure was studied, and the mechanism of soft and hard additives with A-site or B-site substitute changing the piezoelectric properties was discussed. It was found that the rhombohedral-tetragonal morphotropic phase boundary (MPB) of the Na1/2Bi1/2TiO3-6BaTiO3 was not changed obviously.