Dielectric Properties Of BaTiO3 Ceramics Research Articles

Effects of addition of BiFeO3 on phase transition and dielectric properties of BaTiO3 ceramics

Samples of xBiFeO3–(1 − x)BaTiO3 (x = 0, 0.02, 0.04, 0.06, 0.07 and 0.08) were synthesized by solid state reaction technique and sintered in air in the temperature range 1,220–1,280 °C for 4 h. X-ray diffraction data showed that 2–8 mol% BiFeO3 can dissolve into the lattice of BaTiO3 and form single perovskite phase. The crystal structure changes from tetragonal to cubic phase at room temperature when 8 mol% of BiFeO3 was added into BaTiO3. Scanning electron microscope images indicated that the ceramics have compact and uniform microstructures, and the grain size of the ceramics decreases with the increase of BiFeO3 content. Dielectric constants were measured as functions of temperatures (25–200 °C). With rising addition of BiFeO3, the Curie temperature decreases. For the sample with x = 0.08, the phase transition occurred below room temperature. The boundary between tetragonal and cubic phase of the BiFeO3–BaTiO3 system at room temperature locates at a composition between 7 and 8 mol% of BiFeO3. The diffusivity parameter γ for compositions x = 0.02 and x = 0.07 is 1.21 and 1.29, respectively. The relaxor-like behaviour is enhanced by the BiFeO3 addition.

Effect of particle size on the densification and dielectric properties of BaTiO3 ceramics prepared by liquid phase sintering

AbstractUsing starting BaTiO3 powders of various particle sizes, we investigated the densification and dielectric characteristics of BaTiO3 ceramics sintered at low temperature with the addition of ZnO‐B2O3‐SiO2 (ZBS) glass as sintering aids. Scanning electron microscopy, X‐ray diffraction, Raman spectroscopy, and LCR meter were used to examine the structure and dielectric properties. The results indicated that the particle size of raw powders had a dramatic influence on the densification and dielectric properties of BaTiO3 ceramics. The grain size of the final ceramics was almost proportional to the particle size of the starting BaTiO3 powder. Moreover, the tetragonality (c/a ratio) and Curie temperature is increased with the increase of grain size of the BaTiO3 ceramics. The relative density of 96% and the dielectric constant of 1440 were obtained for the BaTiO3 ceramics prepared with the raw powders of average particle size of 800 nm. In addition, the sintering temperature was reduced to 1100 °C due to the addition of 5 wt% ZBS glass.

Low-Temperature Sintering and Microwave Dielectric Properties of Ba2Ti9O20 Ceramics with CaO–B2O3–ZnO Glass Additions

The effect of CaO–B2O3–ZnO (CBZ) glass on the microstructures and microwave dielectric properties of Ba2Ti9O20 ceramics was investigated. With the addition of CBZ glass, the densification temperature of Ba2Ti9O20 can be effectively reduced from 1400 to 880–920 °C. It is found that the addition of CBZ glass (20–30 wt %) can significantly improve the density and dielectric properties of Ba2Ti9O20 ceramics. The dielectric properties of Ba2Ti9O20 ceramics were strongly dependent upon the amount of CBZ glass addition. A dielectric constant (εr) of 27.0, a quality factor (Q ×f) value of 13,400 GHz, and a temperature coefficient of resonant frequency (τf) of 17.8 ppm/°C were obtained for 20 wt % CBZ glass-doped Ba2Ti9O20 ceramics sintered at 920 °C for 2 h.

Low-Temperature Sintering and Microwave Dielectric Properties of Ba2Ti9O20Ceramics with CaO–B2O3–ZnO Glass Additions

Low-Temperature Sintering and Microwave Dielectric Properties of Ba₂Ti₉O₂₀Ceramics with CaO–B₂O₃–ZnO Glass Additions

Low Temperature Sintering and Dielectric Properties of BaTiO3 Ceramics Incorporating Nano-Sized Powders

The densification of nano-sized BaTiO3 (BT) using LiF and LiF-BaCO3 as sintering aids was investigated. The density of the sample containing 1 wt.% LiF and 1 mol% BaCO3 sintered at 900°C could achieve 5.67 g/cm3 (95% of the theoretical density). The temperature-dependence of the dielectric properties was measured from −20 to 125°C. The results showed that using 1 wt.% LiF and 1 mol% BaCO3 as a sintering aid, the BT ceramic sintered at 900°C for 1.5 h could obtain very high room temperature permittivity (ϵ r ∼5382 at 10 kHz) and with relatively small variation with temperature, which is suitable for low temperature cofired ceramic (LTCC) applications.

Effect of Dysprosium Oxide Addition on the Microstructure and Dielectric Properties of BaTiO3 Ceramics

0.2–1.1 mol. % Dy was doped in BaTiO3 ceramics and the doping effect of Dy on the microstructure and the dielectric properties including permittivity and breakdown voltage was studied. The addition of Dy in the BaTiO3 ceramics was found to enhance the dielectric properties, which are attributed to an increase in tetragonality and a significant reduction in the average grain size due to the suppressed grain growth. The doped Dy plays an essential role in the formation of the core-shell structure in the BaTiO3 grains. The 0.8 mol. % Dy-doped BaTiO3 ceramics presented the highest dielectric constant and breakdown voltage due to the increased tetragonality, a remarkably reduced average grain size, and a well-developed core-shell structure in the grains.

The effect of CuO doping on the microstructures and dielectric properties of BaTiO3 ceramics

(1 − x) BaTiO3/xCuO ceramic pellets with x = 0, 0.2, 0.4, 0.6, and 0.8% respectively were prepared by the traditional solid-state reaction method. The effect of CuO doping on the microstructure and dielectric properties of BaTiO3 ceramics has been investigated. SEM and XRD results at room temperature show that the grain size grows with the increase of CuO content under the same sintering conditions and the crystal structure undergoes the mixed phases (pseudocubic/tetragonal) to tetragonal phase transition with the growth of grain size. Regular shape grains with average grain size ~2 μm are detectable in the specimens as CuO dopant content adds up to 0.8% and the crystal structure has completely changed into tetragonal phase. The permittivity increases markedly for CuO dopant content x = 0.2 ~ 0.4% and the dielectric loss decreases significantly after being doped by CuO and down to a minimum value for x = 0.8%. In addition, the permittivity and dielectric loss display a good stability in a broad frequency range comparing that of pure BaTiO3 ceramics.

The Effects of Gd/Nd Co-Doping on the Microstructure and Dielectric Properties of BaTiO3 Ceramics

In order to obtain X7R (-55 to 125 °C, ΔC/C = ±15% or less) ceramics sintered at a middle temperature, the effects of Gd2O3 and Nd2O3 additives on the microstructure and dielectric properties of BaTiO3 (BT)–Nb2O5–ZnO–borosilicate system were investigated. When the amount of Gd2O3 was stable, the dielectric constant at room temperature (ε25 °C) monotonously decreased as the Nd2O3 content increased from 0.1 to 0.7 wt %. Minimal influence was observed on the high temperature coefficient of capacitance (TCC125 °C). In contrast, when the Nd2O3 content remained unchanged and Gd2O3 was increased, the dielectric constant ε25 °C at room temperature first declined and then increased and the TCC125 °C value decreased. Additionally, the TCC125 °C value of BT ceramics was positively correlated to the micro-stress. For Gd/Nd co-doped ceramics, TCC125 °C value was determined only by the Gd2O3 content. BT ceramics sintered at 1140 °C in air have the following properties: ε25 °C> 3000, tan δ≤1.0%, ρ≥1011 Ω·cm and ΔC/C (-55 to +125 °C) ≤ ±7.5%.

Effect of glass powders with spherical shape and fine size on the sintering behavior and dielectric properties of BaTiO3 ceramics

In this study, it was found that BaO-B2O3-SiO2 glass powders with fine particle sizes and spherical shapes improved the sintering characteristics of nanosized BaTiO3 powders. The mean sizes of the prepared glass powders and BaTiO3 powders were 940 nm and 110 nm, respectively. The densities of BaTiO3 pellets containing 0, 1, 3, and 5 mass% of a glass additive were 4.2, 5.2, 5.5 and 5.7 gcm-3, respectively, at a sintering temperature of 900°C. The densities of BaTiO3 pellets sintered at 900°C and containing 5 mass% of the glass additive were similar to that of the pellet sintered at 1280°C and containing no glass additive. Dielectric constants of pellets containing 5 mass% of the glass additive and of pellets containing no glass additive were 1599 and 469, respectively, at a sintering temperature of 900°C. Dielectric constants of pellets containing 1 mass% of the glass additive increased from 602 to 4109 when the sintering temperature was increased from 800 to 1200°C.

Dielectric properties of 3d transition metal substituted BaTiO3 ceramics containing the hexagonal phase formation

The role of transition metals of the 3d series from V (Z = 23) to Zn (Z = 30) is investigated in modifying the crystallographic phase contents, microstructure and the dielectric properties of BaTiO3 ceramics containing ≤10 at% substituents. All the transition metals brought about the phase conversion to hexagonal BaTiO3 and the hexagonality is found to depend on Ba/Ti ratio as well as the processing conditions including the sintering temperature and the post sinter annealing. The er-T characteristics are modified with increasing hexagonality by way of the tremendous decrease in dielectric constant with broad and diminished emax for the mixed phase ceramics giving way to flat er-T curves for totally hexagonal specimens. Doping with >1% Zn2+ or ≥5% Mg2+ also render the ceramics completely hexagonal indicating that the crystal field effects of the 3d orbital electrons are not the cause for the conversion to hexagonal phase. Electron paramagnetic resonance (EPR) spectra of Mn-doped ceramics reveal the prevalence of defect complexes involving oxygen vacancies and different valence states of Mn occupying the Ti-sites within the corner-sharing as well as face-sharing octahedra present in hexagonal BaTiO3. EPR results also indicate defect complexes involving electron localization at Ti-sites and oxygen vacancies around the face-sharing octahedra. On annealing the ceramics in lower oxygen partial pressures at elevated temperatures leads to the reversion to corner shared (Ti3+–VO) defect complex accompanied by the conversion to cubic/tetragonal phase. The alterations in the oxygen vacancy-metal impurity defect complexes and the modifications in the oxygen close packing are the cause for the prevalence of hexagonal BaTiO3 at room temperature.

Core–Shell Structure Analysis of BaTiO3 Ceramics by Synchrotron X‐Ray Diffraction

The shell thickness of a BaTiO3 ceramic with a core–shell structure has been measured by means of synchrotron X‐ray diffraction (XRD). BaTiO3 ceramic is known from transmission electron microscope (TEM)/energy dispersive X‐ray spectroscopy (EDS) observations to have an inhomogeneous microstructure with cores of a pure BaTiO3 and shells doped with additives. It is also known, from XRD observations, that the BaTiO3 cores have a tetragonal lattice structure and the shells are pseudocubic. We have estimated the shell thickness d from the full‐width at half‐maximum (FWHM) of the cubic (400)c peak, using Scherrer's equation. The shell thickness dcal was also evaluated from the volume fraction of tetragonal BaTiO3 using a spherical core–shell model. The two values thus determined agree well, confirming that the BaTiO3 ceramic specimens have a core–shell structure. Our results show that synchrotron XRD is a simple and effective tool for quantitative analysis of the core–shell structure. It enables us to understand quantitatively the relationship between the microstructure and the dielectric properties of BaTiO3 ceramics.

Effect of SnO2 addition on the dielectric properties of Ba2Ti9O20 ceramics in the high-frequency regime

The effect of SnO2 addition on the high-frequency dielectric properties of Ba2Ti9O20 ceramics has been investigated using terahertz time-domain spectroscopy, far-infrared (FIR) reflectivity, and Raman-scattering measurements. The dielectric constants determined from the terahertz and FIR spectra are smaller than that taken in the microwave frequency region. In contrast, the increase of the dielectric loss with increasing frequency is due to some resonance modes above 1THz. Importantly, our data clearly show that the SnO2 (2.4mole%) addition degraded the dielectric properties of Ba2Ti9O20 ceramics, which is ascribed to the deterioration on the coherency of lattice vibrational characteristics for these materials.

Effects of Cerium Doping at Ti Sites and Europium Doping at Ba Sites on Dielectric Properties of BaTiO 3 Ceramics

Two special rare earth elements cerium and europium were chosen to conduct chemical modification of the BaTiO3 structure. The cold-pressing ceramic processing technique was used to prepare barium titanate ceramics doped with Ce at Ti sites and with Eu at Ba sites on the base of formulas Ba(Ti1-xCex)O3(x =0.05, 0.10)(CBT) and (Ba1-yEuy)Ti1-y/8O3(y=0.05, 0.10)(EBT). Associated with structures and microstructures, the effects of cerium and europium doping on dielectric properties of BaTiO3 ceramics were discussed. The CBT ceramics exhibit a pseudo-cubic perovskite structure, while the EBT ceramics exhibit a tetragonal perovskite structure with the exception of the existence of a small percentage of the Eu2Ti2O7 phase. The Curie peak of BaTiO3 shifts towards room temperature at rates of 3 °C/mol Ce atoms and 10 °C/mol Eu atoms (Eu≤5%), respectively. Compared with the CBT ceramics, the EBT ceramics show significant advantages, such as a narrow fine grain size distribution(1 μm), a lower porosity and a higher density(5.85 g/cm3), more stable dielectric-temperature dependence(ɛ′=1600–1800 at t

Influence of 3d-elements on dielectric properties of BaTiO3 ceramics

The microstructure and dielectric properties of Yb-Mn- and Yb-Ni-substituted BaTiO3 ceramics are investigated in this paper. Both Yb-Mn- and Yb-Ni-substituted BaTiO3 ceramics satisfy the X8R specification (−55 ∘C to 150 ∘C, Δ C = ±15% or less) for automotive application when CaZrO3 is incorporated in the formulations. It is found that both Mn and Ni ions can suppress the diffusion of Yb and CaZrO3 into BaTiO3 grains, resulting in formation of core-shell structures in the grains. It is found that Mn is more favorable to stabilize the core-shell structure in BaTiO3 ceramics as compared with Ni.

Low-Fire Processing of BaTiO3 with BaCuO2–CuO

The effects of a liquid-phase-sintering aid, BaCuO2–CuO (BCC), on the densification and dielectric properties of BaTiO3 ceramics have been investigated. The densification temperature of BaTiO3 is greatly reduced from 1300–1350°C down to 1050°C in the presence of BCC. This is attributed to a chemical reaction taking place at the interface of BCC/BaTiO3 during firing. The BaTiO3 dissolves into BCC, forming crystalline phases of BaCuO2, CuO, Cu2O and Ba6Ti17O40, and this enhances the densification kinetics of BaTiO3. For the samples with 2.0–2.5 wt% BCC, a high relative sintered density of >95% is obtained at 1050°C, and the resulting dielectric ceramics have a dielectric constant and dielectric loss in the range of 2200–2400 and <3% at 1 MHz, respectively.

The effects of additive on microstructure and electrical properties of batio3 ceramics

In this paper comparative investigations of microstructure and dielectric properties of BaTiO3 ceramics doped with 1.0 wt% of Nb2O5, MnCO3 and CaZrO3 have been done. BaTiO3 samples were prepared using conventional method of solid state sintering at 13000C for two hours. Two distinguish micro structural regions can be observed in sample doped with Nb2O5. The first one, with a very small grained microstructure and the other one, with a rod like grains. In MnCO3 and CaZrO3 doped ceramics the uniform microstructure is formed with average grain size about 0.5- 2?m and 3-5?m respectively. The highest value of dielectric permittivity at room temperature and the greatest change of permittivity in function of temperature were observed in MnCO3/BaTiO3. In all investigated samples dielectric constant after initially large value at low frequency attains a constant value at f = 6kHz. A dissipation factor is independent of frequency greater than 10 kHz and, depending of systems, lies in the range from 0.035 to 0.25. At temperatures above Curie temperatures, the permittivity of all investigated samples follows a Curie- Weiss law. A slight shift of Curie temperature to the lower temperatures, in respect of Curie temperature for undoped BaTiO3, was observed in all investigated samples.

Effects of B2O3 Addition on the Microwave Dielectric Properties of Ba2Ti9O20 Ceramics

Microwave characteristics of Ba2Ti9O20 ceramics added with different amounts of B2O3 and sintered at high temperatures ranging from 900 to 960°C for 2 h are investigated. It is found that the firing temperature required to densify the Ba2Ti9O20 ceramics is lowered by increasing the B2O3 content. The density and dielectric constants of the B2O3-added ceramics also increase with B2O3 addition. The results of X-ray diffraction (XRD) indicate the presence of five crystalline phases, Ba2Ti9O20, BaZr(BO3)2, BaZrO3, BaTi4O9, and Zn3(BO3)2, in the sintered ceramics, depending upon the amount of B2O3 added. Optimum dielectric properties, i.e., Q=1477 (Q×f=10784), εr=28.3, and τf=-8.2, are obtained for the Ba2Ti9O20 ceramics with 3 wt% B2O3 addition and sintering in air at 940°C for 2 h.

Effect of Ho/Mg Ratio on Formation of Core-shell Structure in BaTiO3 and on Dielectric Properties of BaTiO3 Ceramics

Ceramics were prepared from hydrothermally-synthesized BaTiO3 (100 mol%), BaSiO3 (1.5 mol%), MnO (0.1 mol%) with Ho2O3 (0.5 mol%) and MgO (0.25–1 mol%). The compositions with Ho/Mg molar ratios of 4:4, 4:2, 4:1 were selected for examination. The ceramic samples were sintered at 1340°C (PO2<10-9 Pa) and, then, annealed at 1000°C (PO2<30 Pa). The distribution of Ho and Mg in the samples was examined by transmission electron microscope (TEM) equipped with an element analyzer (EDS). Measurements of temperature dependence of dielectric permittivity over -55–155°C showed that the sample with a Ho/Mg ratio of 4/4 showed the least change of dielectric permittivity with temperature compared to the sample with a high Ho/Mg ratio of 4/1. The material with a Ho/Mg ratio of 4/1 is characterized by the deepest Ho diffusion into BaTiO3 and the slowest decrease of Ho concentration that is considered to result in a formation of a shell with considerable amounts of low-concentrated Ho-containing solid solutions.

Low Temperature Sintering and Microwave Dielectric Properties of Ba2Ti9O20 Ceramics with 3ZnO–B2O3 Addition

Boron and zinc oxide (ZnBO) glass added in dielectric materials have drawn a great attention recently due to the low firing temperature. Microwave dielectric properties of the Ba2Ti9O20-based ceramics with ZnBO addition up to 3 wt% were investigated at the sintering temperatures ranging from 900 to 960°C. Effects of the ZnBO addition on the bulk density, microstructure, and dielectric properties of the Ba2Ti9O20-based ceramics at microwave frequency were elucidated. X-ray diffraction (XRD) results show the presence of five crystalline phases, Ba2Ti9O20, BaZr(BO3)2, BaTi3O7, BaZrO3 and Zn2SiO4 in the sintered ceramics, depending upon the amount of ZnBO addition. Optimum dielectric properties were obtained for the Ba2Ti9O20-based ceramic with 1 wt% ZnBO addition and sintered in air at 940°C for 2 h, having the dielectric properties: Q=1137 (Q×f=8300), εr value=27.3, and τf=2.5 ppm/°C.

Roles of Ba/Ti Ratios in the Dielectric Properties of BaTiO3 Ceramics

The effect of the Ba/Ti ratio on microstructure, dielectric/ferroelectric properties, and domain width was studied using optical microscopy, ɛ(T) curves, D–E hysteresis, and transmission electron microscopy. Although Ti‐excess samples showed abnormal grain growth and a decrease of room‐temperature permittivity due to a liquid phase at grain boundaries, its ferroelectric properties were similar to those of stoichiometric BaTiO3 ceramics. However, in Ba‐excess samples, an increase of permittivity and ferroelectric properties different from those of stoichiometry were found. Changes in domain width and ferroelectric transition behavior indicated that the variation of dielectric properties was related to the internal stress. It is proposed that this internal stress originated from differences in the thermal expansion coefficient between the matrix and the second phase.