Structure and Dielectric Behavior of Yb2O3-MgO Co-Doped 0.92BaTiO3-0.08(Na0.5Bi0.5)TiO3 Ferroelectric Relaxor

Dielectric properties and structure of 0.015Yb2O3-xMgO doped 0.92BaTiO3-0.08(Na0.5Bi0.5)TiO3 ceramics with x = 0.0–0.025 have been investigated. As Yb2O3-MgO was added into the BT-NBT, the phase changes from tetragonal to pseudo-cubic, with the tetragonality c/a decreases from 1.011 to 1.008 and XRD peaks broadened. The combined study of XRD and TEM image revealed a formation of core–shell structure in grains with core of 400–600 nm and the shell of a thickness 60–200 nm. There is a slowly phase transition against temperature from the variable temperature Raman analysis. The ferroelectric relaxor peak of BT-NBT decreases from ~4000 to ~2000 and a new broad dielectric peak with an equivalent maximum (εr′~2300) appears in the temperature dependent dielectric constant curve (εr′-T), which produces a flat εr′-T curve. Sample 0.92BaTiO3-0.08(Na0.5Bi0.5)TiO3-0.015Yb2O3-0.005 MgO and 0.92BaTiO3-0.08(Na0.5Bi0.5)TiO3-0.015Yb2O3-0.01MgO give a εr′ variation within ±14% and ±10% in 20–165 °C. The core–shell microstructure should take account for the flattened εr′–T behavior of these samples.

Structure and electrical properties of Eu-doped SrBi2Nb2O9 ceramics

Structure and dielectric properties of Eu-doped SrBi2Nb2O9 ceramics (with 0, 20 and 35 at.% of Eu), prepared by the solid-state method and sintering, were investigated. XRD, FTIR and SEM measurements were provided to validate the characteristic structural features of the obtained ceramics. For all samples, the orthorhombic structure was identified through XRD analysis. SEM results confirmed that the fabricated samples have relatively dense structure with rod- and plate-like grains typical for Aurivillius layered structures. Dielectric results showed that the doping with Eu decreases dielectric constant and reduces dielectric loss. Movement of the dielectric peak towards higher temperatures appearing at about 400?C with increase of frequency indicates on relaxor behaviour of the sample with 35 at.% of Eu.

High Permittivity and Varistor Properties of SnO2-Zn2SnO4 Composite Ceramics

(1-x)SnO2-xZn2SnO4composite ceramics were prepared by traditional ceramic processing and the varistor, dielectric properties were investigated. With increasing Zn2SnO4content, the breakdown electrical fieldEBand nonlinear coefficientαreaches the minimum of 6.9 V/mm and 2.5 at x=0.206, respectively. In the dielectric spectra, the relative dielectric constantεrexhibits strong frequency dependent character and at 40 Hz,εrfor the sample of x=0.206 reaches a maximum as high as 3×104. In the frequency region lower than 1 kHz, accompanied by the sharp increase of dielectric loss at 40 Hz,εris depressed and a dielectric peak is presented in the spectra with increasing bias voltage. In the low electrical current range of 1.37-20 μA, The barrier heightφBabout 1.0 eV are obtained and it is found thatφBdecreases with increasing measuring current for each sample. Based on the results, the varistor behavior with high dielectric constant is explained by the Schottky barriers at grain boundaries.

Synthesis of Hierarchy-Structural BaTiO3 Powder Used for X8R Multilayer Ceramic Capacitors by Two-Step Soft Chemical Method

Ba0.985Bi0.01TiO3-BaTi1-xZrxO3 powders have been synthesized by two-step soft chemical method to satisfy EIA-X8R specification. Microstructural evaluation conducted by X-ray diffraction and scanning electron microscopy confirms the hierarchical structure of the ceramic grain. The shape of the ε-T curves near the dielectric peak becomes broad with the increase of Zr content. The permittivity of Ba0.985Bi0.01TiO3-BaTi0.9Zr0.1O3 ceramic is ~3000, C/C20 °C is-14.67%, 6.23% and-14.50% at-55°C, 130°C and 160°C, respectively, and the dielectric loss is less than 0.020. This work shows that the two-step soft chemical method is a promising approach for high performance temperature-stable capacitor materials.

Temperature-Dependent Structure of a High-k (Ba,La)(Ti,Ce)O3 Ceramic

The lattice structure of a high-k BL3TC5 [(Ba1-xLax)(Ti1-x/4-yCey)O3 (x = 0.03, y = 0.05)] ceramic with cubic structure at room temperature was investigated using temperature-dependent X-ray diffraction (XRD) and Raman spectroscopy. The XRD results indicated that with increasing temperature, the cubic lattice of BL3TC5 showed a lower coefficient of linear expansion (α = 7.7 × 10-6/°C) relative to the cubic BaTiO3 (9.3 × 10-6/°C), but no abnormal change in cell volume occurred around the dielectric peak temperature Tm (= 38 °C). The peak position of the ~835 cm-1 Raman band induced by the substitution of La3+ ions for Ba sites in BL3TC5 was nearly independent of temperature on each side of Tm, whereas a slight fall (3 cm-1) in the peak position around Tm was detectable. The link between the dielectric peak with DPT and the lattice change was discussed.

Electronic Structure and Optical Properties of SiC Nanotube Material with Silicon Antisite Defect

Based on first-principle calculations, electronic structure and optical properties of a single-walled zigzag SiC nanotube with silicon antisite defect have been investigated. This defect results in the formation of a bump in the surface of the nanotube. No defect energy level is formed in its band gap, which is originated from the resonance between the defect level and conduction band resulting in the defect level entering its conduction band. The most primary dielectric peak in dielectric function parallel to the axis of the nanotube is depressed, while the first peak perpendicular to its axis is enhanced. These results are meaningful for investigations on SiCNT electronic and optical devices.

A Study on the Phase Transformation Behavior and Characteristics of BaTi1-X(Li2/3 Nb2/3 )XO3 Solid Solution

Microstructure, phase transformation behavior and electrical properties of BaTi1-x(Li2/3Nb2/3)xO3 with x=0.01-0.40 ceramics have been investigated. Only perovskite phase is detected for all the compositions. The room temperature state of BaTi1-x(Li2/3Nb2/3)xO3 ceramics experiences a transformation from a ferroelectric phase to a paraelectric phase with increasing x. Meanwhile, the permittivity of BaTi1-x(Li2/3Nb2/3)xO3 ceramics reduces, while the Q×f value increases. A degree of frequency dispersion of dielectric peak is obviously increased as x increases from 0.01 to 0.10. It is of great interest that a dielectric abnormity represented by a broad dielectric peak at 200-400K is observed for the composition with x=0.40.

Preparation and Relaxor Behavior of Barium Strontium Titanate Glass-Ceramics Doped Si-B-O Sintered from Sol-Gel Derived Powders

The structural and dielectric properties of Si-B-O doped Ba0.60Sr0.40TiO3(BST) glass-ceramics prepared by using sol-gel derived powders have been investigated. The secondary phase of BaTi2Si2O8is clearly observable in BST glass-ceramics when the concentration of Si-B-O is equal to or more than 20mol%. The samples with high Si-B-O doping levels can be sintered into dense microstructure in low sintering temperature (below 1000°C). The dielectric peaks of BST glass-ceramics are markedly suppressed, broadened and shifted to low temperature with increasing the concentration of Si-B-O, accompanying an increased diffuseness of the dielectric peak due to the ionic substitution, which follows well the Lorenz-type relation.