Converse flexoelectric coefficient f(1212) in bulk Ba0.67Sr0.33TiO3

Enhanced flexoelectricity in perovskite ceramics and single crystals has been reported before. In this letter, 3-3 ceramic-ceramic Ba0.6Sr0.4TiO3/Ni0.8Zn0.2Fe2O4 composite with a colossal permittivity was employed in the conventional pure bending experiment in order to examine the transverse flexoelectric response. The measured flexoelectric coefficient at 30 Hz is 128 μC/m and varies to 16 μC/m with the frequency increasing from 30 Hz to 120 Hz, mainly due to the inverse correlation between the permittivity and the frequency. This result reveals the permittivity dependence of flexoelectric coefficient in the frequency dispersion materials, suggesting that the giant permittivity composites can be good flexoelectric materials

Structural and electrical characterization of CeAlO[sub 3] ceramics

The crystal structure and electrical properties of CeAlO3 ceramics prepared by the mixed oxide route have been investigated. X-ray and electron diffraction data show the room temperature structure to be described by the tetragonal I4/mcm space group [a = 5.3253(5) Å and c = 7.5860(9) Å; Z = 4, and theoretical density, Dx = 6.64 g/cm3]. CeAlO3 ceramics sintered at 1500 °C under flowing 5%H2–95%N2 gas for 4 h reach ∼ 94% of Dx with a microstructure of randomly distributed equiaxed grains of average grain size ∼ 2 μm. Conventional transmission electron microscopy reveals needle-shaped ferroelastic domains in some grains. The relative permittivity εr of CeAlO3 ceramics is ∼ 18–20 in the range of ∼ 10–300 K. At room temperature and microwave frequencies, CeAlO3 ceramics exhibit εr ∼ 20.7, Qfr ∼ 40 117 GHz (at 9.5 GHz), and τf ∼ −57 ppm/K. The ion polarizability for Ce3+ is calculated to be 4.46 Å3. Revised dielectric polarizabilities for rare-earth lanthanides are also presented

Synthesis, dielectric and impedance spectroscopy study of temperature stable Ta2O5 modified 0.85BaTiO3-0.15Bi(Mg0.5Ti0.5)O3 ceramics

In the present study, 0.85BaTiO3–0.15Bi(Mg0.5Ti0.5)O3-xTa2O5 (x = 0, 0.01, 0.015, 0.02, 0.025) processed via the conventional mix oxide route. The phase, microstructure, and dielectric properties were studied. Single perovskite phase developed and studied via XRD. A Dense microstructure for each composition was developed with the pseudo-crystal structure. Low grain size 1000 and low dielectric loss (tanδ <2.5 %) is obtained for x ≤ 0.020, with high stability over a broad range of temperatures (<0 °C to 180 °C). These compositions are considered to be suitable for designing X9R capacitors. In complex impedance analysis, the decreasing value of the bulk impedance upon increasing the temperature revealed the negative temperature coefficient of resistance (NTCR) behavior. The small conductivity and high activation energy value for x = 0.01 demonstrate the temperature stability of this ceramic

Structure and microwave dielectric properties of Ca1− xY xTi1− xAl xO3 (CYTA) ceramics

The structure and dielectric properties of Ca1-xYxTi1-xAlxO3 (CYTA) ceramics prepared by the mixed-oxide route have been investigated. CYTA forms a complete solid solution with an orthorhombic perovskite structure. Residual. Y4Al2O9 and Y3Al5O12 resulting from incomplete reaction are observed for >= 0.9. Scanning electron microscopy shows that CYTA ceramics exhibit uniform microstructures, with an average grain size that decreases from similar to 200 mu m at x 0 to similar to 10 mu m at x = 1.0. Transmission electron microscopy of CYTA (x = 0.3) ceramics reveals the presence of ferroelastic domains, and electron-diffraction patterns are indexed on the Pnma space group, consistent with an a(+)b(-)b(-) octahedral tilted structure. The relative permittivity, Er, decreases continuously from 170 to 12, while the microwave quality factor, Q(.)f(r), increases from 10,000 to 12,000 GHz, for x = 0 and 1, respectively. CYTA (x ceramics exhibit epsilon(r) similar to 38, Q(.)f(r) of similar to 14,212 GHz, and a temperature coefficient of resonance frequency, tau(f) of -14 ppm/degrees C. Small additions of acceptor (0.3 wt% ZnO) or donor (I wt% Nb2O5) dopants decrease Q(.)f(r) by similar to 20-30%, respectively. 0.30)

Homogeneous/Inhomogeneous-Structured Dielectrics and their Energy-Storage Performances

The demand for dielectric capacitors with higher energy-storage capability is increasing for power electronic devices due to the rapid development of electronic industry. Existing dielectrics for high-energy-storage capacitors and potential new capacitor technologies are reviewed toward realizing these goals. Various dielectric materials with desirable permittivity and dielectric breakdown strength potentially meeting the device requirements are discussed. However, some significant limitations for current dielectrics can be ascribed to their low permittivity, low breakdown strength, and high hysteresis loss, which will decrease their energy density and efficiency. Thus, the implementation of dielectric materials for high-energy-density applications requires the comprehensive understanding of both the materials design and processing. The optimization of high-energy-storage dielectrics will have far-reaching impacts on the sustainable energy and will be an important research topic in the near future