Jingji Zhang

Raman and dielectric study of Ba0.4Sr0.6TiO3–MgAl2O4 tunable microwave composite

(1−x)Ba0.4Sr0.6TiO3–xMgAl2O4 (x=0.00, 0.05, 0.10, 0.20, and 0.30) composite ceramics have been synthesized by the solid-state reaction, and its structural and dielectric properties have been systematically characterized. Two crystalline phases, a cubic perovskite structure Ba0.4Sr0.6TiO3 (BST) and a face-centered-cubic spinel structure MgAl2O4 (MA), are clearly visible for x≥0.05. As the MA content increases, the composite ceramics show an increased degree of deviation from the Curie–Weiss law and an increased diffuseness of the dielectric peak. Meanwhile, the tunability of composite ceramics increases. Raman analysis clearly indicates that the incorporation of MA lowers the permittivity and degrades the quality factor of BST composites, which is ascribed to the deterioration on B-site ordering of ABO3 perovskite structure.

Structure?dielectric properties relationship in Mg?Mn co-doped Ba0.4Sr0.6TiO3/MgAl2O4 tunable microwave composite ceramics

xMgO?yMnCO3?0.70(1 ? x ? y)Ba0.4Sr0.6TiO3?0.30(1 ? x ? y)MgAl2O4 (where x, y = 0.0?wt% and x = 1.0 wt%, y = 0.5, 1.0, 2.0, 5.0, 10.0?wt%) composite ceramics synthesized by the solid-state reaction show two crystalline phases, corresponding to the Ba0.4Sr0.6TiO3 and MgAl2O4 phases. At a low MnCO3 content (y ? 2.0?wt%), weak diffuseness is visible, while strong diffuseness is observed for a higher MnCO3 content. For x = 0.01 and 0.01 ? y ? 0.02, high tunability is attributed to the small cooperative displacements of Ti4+ ions in the close packed oxygen octahedra of the BST system. The Q value gradually increases with y, potentially due to the microstructural evolution of the BST lattice structure characterized by Raman spectra. Interestingly, the high Q value of the composition with x = 0.01 and y ? 0.05 is in a wide frequency range, which may play an important role in the engineering of the electric-field tunable microwave elements.

Infrared dielectric response and Raman spectra of tunable Ba0.5Sr0.5TiO3–Mg2TiO4 composite ceramics

Dielectric properties of (1−y)Ba0.5Sr05TiO3–yMg2TiO4 (y=0.5–0.8) composite ceramics were studied by using spectroscopic techniques. Increasing the concentration of Mg2TiO4 resulted in hardening of the softest mode, which is responsible for the decrease in the intrinsic permittivity and dielectric loss with increasing y. The soft mode hardens with y and becomes harmonic, which caused the reduction in tunability of the Ba0.5Sr05TiO3–Mg2TiO4 composite ceramics. Raman spectra revealed that linewidth of the MgO4 bending vibration decreases with increasing y, confirming the increase in intrinsic quality factor with y.

Preparation and Piezoelectric Properties of (h00)-Oriented BaTiO3 Ceramics by Tape Casting

(h00)-oriented BaTiO3 ceramics were prepared by tape casting using plate-like BaTiO3 particles as a template. XRD results showed that the degree of orientation of the ceramics is increased from 0.0% to 85.3% by the addition of BaTiO3 template from 0 wt% to 15 wt%, then decreased to 40.7% with further increasing the template to 30wt%. Their piezoelectric properties were measured using a resonance–antiresonance method and d33 meter. It is showed that the piezoelectric properties of oriented samples were increased with increasing degree of orientation. The mass fraction of the template was optimized to achieve improved piezoelectric properties, which was found to be 85.3% with a piezoelectric constant d33 of 320 pC/N.

Dielectric relaxation in MgO-doped tunable Ba0.4Sr0.6TiO3?MgAl2O4 composite ceramics

xMgO?0.70(1 ? x)Ba0.4Sr0.6TiO3 (BST)?0.30(1 ? x)MgAl2O4 (MA) (x = 0, 1, 2, 5, 10?wt%) composite ceramics have been prepared by solid state reactions. Three phases, corresponding to the BST, MA and MgO phases, are clearly visible in the composite ceramics when x is equal to or more than 5?wt%. A dielectric peak with very strong frequency dispersion is observed for all samples. With increasing x, the composite shows an increased degree of deviation from the Curie?Weiss law and an increased diffuseness of the dielectric peak. The permittivity exhibits relaxor behaviour with the frequency-dependent temperature of the permittivity peak Tm satisfying the Vogel?Fulcher formula. As MgO increases, the activation energy Ea moves from 39.1 to 65.6?meV, possibly due to more defect pairs and . The room-temperature permittivity decreases from ~390 for x = 0.01 to ~280 for x = 0.10 while the tunability still remains constant ~9.0% under 30?kV?cm?1 biasing.

Dielectric Tunable Properties of Ba0.4Sr0.6TiO3-Mg2SiO4 Microwave Composite Ceramics

(1−x)Ba0.4Sr 0.6 TiO3(BST)–xMg2SiO4(MS) (x = 0.00, 0.05, 0.10, 0.20, 0.40, 0.50 and 0.60) composite ceramics have been prepared by the traditional solid state reaction, and its structural and dielectric properties have been characterized. Only two phases, corresponding to the BST and MS phases, are clearly visible for x ≥ 0.20. The permittivity is tailored from 763 to 75 by manipulating the addition of MS from 5 wt% to 60 wt% and the tunability decreases from 11.2% to 6.4% measured at 10 kHz. Meanwhile, the Q value of composite ceramics is decreased from 351 to 128.