Xiujian Chou

Dielectric properties and relaxor behavior of rare-earth (La, Sm, Eu, Dy, Y) substituted barium zirconium titanate ceramics

Based on the Ti-vacancy defect compensation model, (Ba1−xLnx)Zr0.2Ti0.8−x∕4O3 (Ln=La,Sm,Eu,Dy,Y) ceramics have been fabricated via the conventional solid-state reaction method. The microstructures, dielectric properties, and ferroelectric relaxor behavior of (Ba1−xLnx)Zr0.2Ti0.8−x∕4O3 ceramics have been investigated. The results indicate that rare-earth ions with various ionic radii enter the unit cell to substitute for A-site Ba2+ ions and inhibit the grain growth. The typical ferroelectric relaxor behavior is induced due to the rare-earth ions substitution. The diffuseness of the phase transition and the degree of ferroelectric relaxor behavior are enhanced, the TC is remarkably shifted to lower temperature, and the tunability is suppressed with the increase of x value and substituted ionic radius for (Ba1−xLnx)Zr0.2Ti0.8−x∕4O3 (x=0.005–0.04, Ln=La,Sm,Eu,Dy,Y) ceramics. Tunable ferroelectric materials with moderate dielectric constant and low dielectric loss can be obtained by manipulating the doping am...

Dielectric tunable properties of low dielectric constant Ba0.5Sr0.5TiO3–Mg2TiO4 microwave composite ceramics

Ba0.5Sr0.5TiO3–Mg2TiO4 composite ceramics are fabricated via the conventional solid-state reaction method. The microstructures, dielectric tunability, and microwave properties of composite ceramics are investigated. The dielectric constant is tailored from 335 to 35 by manipulating the addition of Mg2TiO4 from 50% to 80% weight ratio and the tunability is 10.8% measured at 10kHz for the 80% Mg2TiO4 addition. The composite ceramics with high Q value (>200) at L band are useful for potential tunable microwave device applications in the wireless communication system.

Dielectric Properties of Mg-Doped Ba0.6Sr0.4TiO3 Ceramic Sintered at a Low Temperature with Li2O Additve

Dielectric properties of Mg-doped Ba0.6Sr0.4TiO3 ceramics with the aid of Li2O have been investigated. 3.0wt% Li2O additive samples can be sintered at 900°C for 4h and sintering temperature remarkably decrease. Phase and microstructure of these samples were analyzed using XRD and SEM. Results show no obvious secondary phase and decreased grain-size as MgO content increased. Dielectric constant is decreased and the Curie temperature is shifted to low temperature and the peaks are suppressed and broaden with the increase of MgO. Tunability is decreased from about 30% to 15% with MgO content increasing from 0.15wt% to 5.0wt% under applied electric field of 40 kV/cm.

Microwave Property of Low-Temperature-Sintered Ba1-xSrxTiO3 Ceramics with B-Li Glass Sintering Aid

This paper reports on fabrication and characterization of low-temperature-sintered barium-strontium titanate (BST) ceramics with B-Li glass as sintering aid. With the addition of B-Li glass, the sintering temperature of BST can be effectively reduced from 1350 to 920°C due to the presence of a liquid phase. The effects of B-Li glass addition on phase composition, microstructure, dielectric properties, and microwave properties of the BST ceramics were sytematically investigated. The sample (Ba0.50Sr0.50TiO3) with 5.0 wt% B-Li sintered at 920°C for 5 h exhibits optimized room temperature dielectric properties, including a moderate dielectric constant (ϵ = 1051), a low dielectric loss (0.0048) and a high tunability (31%) at dc electric field of 45 kV/cm and 10 kHz. At 1.150 GHz, it possesses a dielectric constant of 695 and Q value of 207.

Dielectric and Tunable Properties of Ba0.6Sr0.4TiO3-Mg2TiO4 Composite Ceramics for Phase Shifter Applications

The composite ceramics of barium strontium titanate (Ba 0.6 Sr 0.4 TiO 3 , BST) with microwave dielectric magnesium titanate (Mg 2 TiO 4 , MT) were prepared using the traditional ceramic process. The XRD patterns analysis showed that the two-phase structures of BST and MT were formed. SEM observation revealed that the grain sizes were consistent with the BST. There is a significant depression in dielectric constant. The dielectric constant was decreased to 254 with composition of 40wt%BST-60wt%MT and dielectric loss was also reduced to 0.0007 at measurement frequency of 10 kHz. The tunability is about 34% for 40wt%BST-60wt%MT composition under applied electric field 3 kV/mm at 10 kHz. In addition, the microwave property of the composite ceramics was optimized compared with pure BST.