Ferroelectricity of 30 nm BaTiO3 ceramics prepared by high pressure sintering

BaTiO₃ ceramics with a grain size of 30 nm were prepared at 6 GPa, 1,273 K using a three-step high pressure sintering method. The sintered bulk is uniform and the relative density is above 96% of the theoretical value. Similar to normal BaTiO₃, successive phase transitions were observed in 30 nm BaTiO₃ ceramics by X-ray diffraction method with the change of temperature. After annealing in O₂, a broadened ferroelectric transition was obtained at 398 K and the relative dielectric constant is 1,700 at 10 kHz.     

Effect of BaTiO3 size on dielectric property of BaTiO3/PVDF composites

The BaTiO₃/polyvinylidene fluoride (BaTiO₃/PVDF) polymer-based composites with different size and concentration of BaTiO₃ particles were fabricated via a simple physical mixing and subsequently hot-press processing. Effect of the filler size and frequency on the dielectric properties of the BaTiO₃/PVDF binary composites was discussed. The result shows that the BaTiO₃ size has an effect on the morphology of the BaTiO₃/PVDF composites. The composites with 0.2 and 0.3 μm BaTiO₃ exhibit high dielectric permittivity than those with 0.4 and 0.5 μm BaTiO₃. The composite with 0.4 μm BaTiO₃ has a minimum dielectric permittivity except one with 0.1 μm BaTiO₃. Dielectric loss of the BaTiO₃/PVDF binary composites changes slightly with the BaTiO₃ sizes. The ternary BaTiO₃/PVDF composites with 0.1 and 0.7 μm BaTiO₃ in coexistence exhibit good dielectric properties. As a result, the BaTiO₃/PVDF ternary composites in this study may have a promising application as dielectric material in embedded capacitor.     

High temperature electrical characterization of nano-crystalline BaTiO3 synthesized using Ba(NO3)2 and TiO2

The reaction of Ba(NO₃)₂ with TiO₂ was studied by thermogravimetric (TG) and differential scanning calorimetric (DSC) techniques up to 1000°C and in nitrogen atmosphere. It was found that the formation of BaTiO₃ takes place above 600°C. BaTiO₃ powder was prepared by calcination of Ba(NO₃)₂ and TiO₂ precursor mixture at 800°C for 8 h. X-ray diffraction analysis of the synthesized BaTiO₃ confirmed the formation of tetragonal phase. Average crystallite size was found to be 44 nm, For the electrical and morphological characterization pellets of the obtained powder were sintered at 1000 °C for 12 h. Scanning electron micrograph (SEM) exhibits spherical and rod shaped grains. The dielectric constant, dissipation factor, complex plane impedance and ac conductivity of the sintered pellet has been measured in the temperature range of 40–600°C and frequency range of 100 Hz–2 MHz. DC conductivity of the sample was obtained from the impedance data. The conductivities (both ac and dc) and relaxation time (τ) exhibit two regions of temperature dependence, namely region I, which represents (280–450°C) and region II, which governs (450-600°C). Conduction and relaxation in both the temperature regions are explained in terms of hopping of electrons and doubly ionized oxygen vacancies (V_O^??).     

Low-temperature sintering of BaTiO3 with Mn-Si-O glass

In order to reduce sintering temperature and prevent adverse dielectric effects, pure BaTiO₃ powder with the addition of Mn-Si-O glass was sintered in the temperature range of 1175–1300°C. Microstructural observation showed that BaTiO₃ grains of the sintered samples only grew from the initial 400 nm to an average of 430 nm between 1175–1275°C for 1 h, or sintered at 1250°C as long as 27 h. Abnormal BaTiO₃ grains are not found in the sintered samples. The microstructure and phase analysis showed that the dielectric properties, tetragonality, and grain growth of BaTiO₃ are closely controlled by the formation of the liquid phase, newly formed Ba₂TiSi₂O₈ grains, and Mn solid solution in BaTiO₃ grains.     

Bulk dense nanocrystalline BaTiO3 ceramics prepared by novel pressureless two-step sintering method

In this paper, we investigate preparation of bulk dense nanocrystalline BaTiO₃ ceramics using an unconventional two-step sintering strategy, which offers the advantage of not having grain growth while increasing density from about 73 to above 99.6%. Isothermal and constant grain size sintering have been carried out to high density in pure BaTiO₃ system. The kinetics of this method is also discussed, which exploits the different kinetics between densification diffusion and grain boundary mobility. Using this method, bulk dense ceramics with a grain size of 8–10 nm was obtained successfully at a very low sintering temperature.     

Ferroelectric relaxor behavior in Ba0.925Dy0.075TiO3 ceramic

Temperature and frequency dependence dielectric permittivity of Ba_0.925Dy_0.075TiO₃ ceramic has been studied in the temperature range of 100 K to 350 K at the frequencies, 1 Khz, 10 KHz, 100 KHz and 1 MHz for the first time. Diffuse phase transition and frequency dispersion is observed in the permittivity-vs-temperature plots. This has been attributed to the occurrence of relaxor ferroelectric behavior. The observed relaxor behavior has been quantitatively characterized based on phenomenological parameters. A comparison with the Zr doped BaTiO₃ has also been presented. The microstructure of as sintered samples shows a dense and almost uniform micrograph with some impurity phases, and the grains are almost spherical.     

PREPARATION OF BaTiO3 FILMS FOR MLCCS BY DIRECT VAPOR DEPOSITION

ABSTRACT

BaTiO₃ films were deposited by the direct vapor deposition (DVD) technique to prepare thin dielectric layers for multilayer ceramic chip capacitors (MLCCs). The BaTiO₃ films were successfully prepared by co-evaporation of the BaTiO₃ ceramic and Ti metal source. The films deposited at room temperature and 600°C were amorphous and crystalline phases, respectively. The intensity of (110) and (111) peaks increased as Ba/Ti ratios were close to stoichiometric composition. BaTiO₃ films deposited with e-beam power of 700 W showed the deposition rate of 33 nm/min. The dielectric constant and dissipation factor of BaTiO₃ films measured at 1 kHz were 150～ 180 and 2～ 5%, respectively. The capacitance decreased with increasing the temperature and varied only between 787pF and 752pF in the temperature range 15～ 125°C.     

Synthesis of BaTiO3 by soft chemistry routes

In this paper we report a comparison concerning the properties of BaTiO₃ (BTO) ceramics obtained by two soft chemical routes, modified Pechini method and thermal decomposition of oxalate-based precursor. XRD data show the formation of single phase BaTiO₃ with tetragonal symmetry when the polymeric citrate-based precursor was annealed at 850 °C, 2 h. In the case of oxalate based-precursor, longer thermal treatment is required to obtain BaTiO₃ free of any secondary phases. For BaTiO₃ powders prepared by modified Pechini method, TEM and SEM investigations revealed the obtaining of uniformly sized particles forming spherical agglomerates inside large, non-uniform and partially sintered aggregates. The powders synthesized via oxalate route show particles of various sizes, with the same tendency of spherical agglomerates formation, but unlike the modified Pechini synthesis, more uniform and smaller aggregates with well-defined hexagonal-like shape were noticed. The relative permittivity values of 6,478 and 5,088 at Curie temperatures of 127 and 130 °C and low dielectric losses (tan δ?=?0.012) at room temperature were obtained for ceramic samples synthesized via Pechini method and oxalate route, respectively.     

Study of diffuse PhaseTransition behavior in Bi and Li Co-substituted barium titanate ceramics

The effect of Bi and Li co-substitution in BaTiO₃ ceramics on its structural, dielectric and ferroelectric properties has been investigated. Bi and Li co-substituted BaTiO₃ with general formula Ba_(1-x)(Bi,Li)_xTiO₃ (x = 0, 0.02, 0.04 and 0.08) is synthesized by solid state reaction method using microwave heating. The XRD patterns revealed that the single phase tetragonal structure with space group P4mm is formed. The Raman study also shows that the prepared samples have tetragonal symmetry. The frequency and temperature dependent dielectric study on the above set of ceramics were carried out at four different frequencies (1 kHz, 10 kHz, 100 kHz and 1 MHz) and in the temperature range of 30–250 °C. The results reveal that the samples are exhibiting diffused phase transition, and there is a clear deviation from normal Curie–Weiss law. The diffused phase transition property in Bi and Li co-substituted BaTiO₃ ceramics make it more attractive for technological applications. The diffuseness is analyzed using a phenomenological theory of diffuse ferroelectric phase transitions. The room temperature P-E hysteresis loops of all these ceramic samples are investigated. The results show that remnant and spontaneous polarization has decreased with an increase of Bi and Li concentrations. This could be the result of an increased in domain pinning.     

Phase compositions and microwave dielectric properties of MgTiO<Subscript>3</Subscript>-based ceramics obtained by reaction-sintering method

MgTiO₃-based microwave dielectric ceramics were prepared successfully by reaction sintering method. The X-ray diffraction patterns of the sintered samples revealed a major phase of MgTiO₃-based and CaTiO₃ phases, accompanied with Mg₂TiO₄ or MgTi₂O₅ determined by the sintering temperature and time. The microwave dielectric properties had a strong dependence of sintering condition due to the different phase compositions and the microstructure characteristics. The ceramics sintered at 1360 °C for 4 h exhibited good microwave dielectric properties: a dielectric constant of 20.3, a high quality factor of 48,723 GHz (at 9GHz), and a temperature coefficient of resonant frequency of ?1.8 ppm/^oC. The obtained results demonstrated that the reaction-sintering process is a simple and effective method to prepare the MgTiO₃-based ceramics for microwave applications.     

Fabrication and characterization of micropatterned barium titanate ceramics

A new patterning method combining electron beam (EB) lithography and electrophoretic deposition (EPD) for fabricating micropatterned barium titanate (BaTiO₃) thin films was investigated. At first, resist molds with high resolution were prepared using EB lithography on Pt/Ti/Si substrates. Then BaTiO₃ nanoparticles were deposited on the substrates by EPD from a transparent suspension of monodispersed BaTiO₃ nanoparticles; a mixed solvent of 2-methoxyethonal and acetylacetone with a 9:1 volumetric ratio was used as a dispersion medium. The nanoparticles with an average size of about 10 nm were synthesized at a low temperature of 90 °C by a high concentration sol-gel process. EPD layers superfluously deposited on the resist molds were mechanically polished away, followed by chemically removing the molds in a resist remover to leave micropatterns of BaTiO₃ nanoparticles on the substrates, which were finally sintered to yield micropatterned BaTiO₃ ceramic thin films. The method developed may be used to fabricate other micropatterned electroceramic thin films.     

Influence of Space Charge Layers on the Dielectric Properties of Ba0.6 Sr0.4TiO3 Nanostructured Thin Films

Barium strontium titanate (Ba_0.6Sr_0.4TiO₃) nanostructured thin films have been deposited on platinized silicon substrates by the sol-gel method. The as-fired films were found to be amorphous, which crystallize to cubic phase after annealing at 550°C in air for one hour. The low-frequency dielectric responses of the BST films were measured as functions of frequency range from 1 kHz to 1MHz. The thickness dependence dielectric constant of the BST thin films were measured in the temperature range from ?150°C to 150°C at 100 kHz and discussed in the light of an interfacial dead layer. All the samples showed a diffuse type phase transitions. Both the dielectric constant and loss tangent showed anomaly peaks at about 10°C, which corresponds to a tetragonal ferroelectric-to-cubic paraelectric phase transition.     

Effects of dysprosium oxide addition in bismuth sodium titanate ceramics

This research focuses on the preparation and characterization of dysprosium-doped bismuth sodium titanate (BNT) ceramics. The compounds were prepared using the conventional mixed-oxide method. The amount of dysprosium oxide used was varied from 0 to 2 at.%. The mixed powders were calcined at 800 °C and checked for phase purity using X-ray diffraction technique. The powders were then cold-pressed into small pellets which were subsequently sintered at 1050 °C for 2 h. The results from density measurement and SEM micrographs showed that highly dense and high-purity ceramics were obtained. The grain size of Dy-doped samples was found to decrease with increasing Dy content. Compared to pure BNT, the addition of Dy₂O₃ in BNT ceramics slightly increased the dielectric constant values near room temperature. In addition, the Dy doping resulted in a more diffused transition temperature, less frequency dependence of the dielectric constant and very low values of the dielectric loss.     

The tunability and dielectric properties of the compositionally graded Ba(Zr x Ti1−x )O3 thin films

The compositionally graded Ba(Zr _x Ti_1?x )O₃ films with a compositional gradient from BaTiO₃ to BaZr_0.35Ti_0.65O₃ were fabricated on LNO-buffered Pt/Ti/SiO₂/Si substrates by a sol-gel deposition method. In order to confirm the compositional gradient, a combination of X-ray Photoelectron Spectroscopy (XPS) and Ar ion etching was employed to produce the composition depth profile. Dielectric constant peaks, common to a ferroelectric transition, were not observed in the temperature range from ?50 to 100 °C, within which the dielectric constant showed negligible temperature dependence. The compositionally graded Ba(Zr _x Ti_1?x )O₃ thin films with weak temperature dependence of tunability could be attractive materials for situations in which precise control of temperature would be either impossible or too expensive.     

Effect of Gd amphoteric substitution on structure and dielectric properties of BaTiO3-based ceramics

BaTiO₃-based ceramics (doped with a small amount of Ni²⁺, Mn²⁺, Nb⁵⁺, Ca²⁺ and Zr⁴⁺) with various Gd₂O₃ concentrations were prepared by the conventional solid-state reaction method. Effects of Gd₂O₃ doping concentrations on the structure and dielectric properties were investigated. It was deduced from XRD patterns that different substitution sites of Gd³⁺ ions could be affected by Gd₂O₃ doping amount. Gd³⁺ tended to occupy Ba-site when Gd₂O₃ concentration was less than 0.25 mol%. With increasing Gd₂O₃ doping amount to 0.3 mol%, Gd³⁺ substituted into both Ba- and Ti-site which contributed to an obvious improvement on dielectric constant of BaTiO₃-based ceramics. Influences of the Gd³⁺ amphoteric substitution on the improvement of the dielectric constant were discussed based on the self-compensation mechanism.     

Preparation and characterization of high T c (1−x) BiScO3−xPbTiO3 ceramics from high energy ball milling process

(1-x)BiScO₃?xPbTiO₃ powders were synthesized from a mixture of the oxides Bi₂O₃, Sc₂O₃, PbO and TiO₂ using a Fritsch P4? vario-planetary ball milling systems. The pure perovskite structure of BS-PT powder can well be obtained and the crystallite size of the powders was greatly reduced to 18–25 nm after milling 4 h. The rhombohedral–tetragonal phase boundary was observed for the ceramics sintered at 1,000–1,100 °C when x was around 0.64 and 3–7 μm grain size was obtained, which is smaller than traditional method. High Curie temperature (T _c) and high dielectric constant can be obtained at the morphotropic phase boundary (MPB). As PbTiO₃ contents increased from 60 to 68 mol%, the Curie temperature T _c shifted toward higher temperature and the maximum dielectric constant increased. The experimental results demonstrate that the high-energy ball milling process is a promising method to prepare BS-PT materials.     

Effects of various oxide fillers on physical and dielectric properties of calcium aluminoborosilicate-based dielectrics

Physical and dielectric properties of LTCC (low temperature co-fired ceramics) materials based on a typical calcium aluminoborosilicate glass and various fillers such as Al₂O₃, BaTiO₃, CaTiO₃, TiO₂, ZrO₂, MgO and SiO₂ were investigated. Densification, crystallization and thermal and dielectric properties were found to strongly depend on the type of filler. The XRD patterns of Al₂O₃, BaTiO₃, CaTiO₃ and MgO samples demonstrated crystalline phases, CaAl₂Si₂O₈, BaAl₂Si₂O₈, CaTiSiO₅ and CaMgSi₂O₆, respectively, as a result of firing at 850 °C. For the sample containing CaTiO₃ filler, specifically, dielectric constant increased drastically to approximately 19.9. A high quality factor of >210 and a high TCE (temperature coefficient of expansion) of >8.5 ppm/°C were obtained for the composition containing MgO or SiO₂. Near zero TCF (temperature coefficient of frequency) was obtained for the samples containing TiO₂. The purpose of this work is to investigate the effects of various ceramic fillers on physical and dielectric properties and ultimately to provide the technical guidelines for the proper choice of filler in various LTCC systems.     

Structural and Dielectric Properties of Ca Doped Barium Iron Niobate

Ceramic materials with high dielectric constant are being used in many electric and electro-optics applications. Ca substituted barium iron niobate with general formula (Ba_1-xCa_x) (Fe_0.5Nb_0.5)O₃ with x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 were prepared by conventional solid state reaction method. Structural properties were investigated using X-ray diffraction and scanning electron microscope. Two types of phases were observed for 0.4 ≤ x ≤ 08. Dielectric constant and loss tangent were measured using impedance analyzer in the frequency range of 20 Hz–1 MHz at room temperature. Dielectric constant and loss tangent were found to decrease with increasing the frequency. A relatively good combination of dielectric constant and loss tangent was obtained for x = 0.2 (?_r = 1441 and tan δ = 0.19) at 10 KHz.     

Microwave-Hydrothermal Synthesis of Ni0.53Cu0.12Zn0.35Fe2O4/SiO2 Nanocomposites for MLCI

The nanocomposites of NiCuZnFe₂O₄-SiO₂ were prepared using Microwave-Hydrothermal method at 160°C/45 min.The as-synthesized powders were characterized using X-ray diffraction and Transmission Electron Microscope (TEM).The average particle size of the powders were found to be ～20 nm.The powders were densified at 900°C/30 min using Microwave sintering method. The sintered composite samples were characterized using XRD and Scanning Electron Microscopy (SEM). Crystallite size of the ferrites decreases with an increase of SiO₂ content. The density of the composites varies of 93–98% of theoretical density. The densities of the present composites were increasing with the addition of SiO_2. The bulk densities of the present composites were increasing with the addition of SiO₂. The structural changes in these samples were characterized using Fourier Transform Infrared Spectrometer (FTIR) in the 400–4000 cm^?1. The bands in the range of 580–880 cm^?1 show a slight increase in intensity, which could be ascribed to the enhanced interactions between the NiCuZnFe₂O₄ clusters and silica matrix. The resistivity of the sintered samples was increased with an addition of ferrite content. The real and imaginary parts of permittivity and permeability were measured in the frequency range of 1 MHz–1.8 GHz.The addition of SiO₂ alters the values of dielectric constant and permeability which is useful to the Multilayer Chip Inductors (MLCI) fabrication.     

Synthesis and magnetic properties of BaTiO3-CoxFe3-xO4 core-shell particles by homogeneous coprecipitation

BaTiO₃-Co_xFe_3-xO₄ (x is regulated by the R value, R = M (FeCl₂?4H₂O)/M (CoCl₂?6H₂O), the molar ratio of FeCl₂?4H₂O to CoCl₂?6H₂O) core-shell particles were synthesized by facile homogeneous coprecipitation method utilizing urea as pH adjuster and air as oxidizer. The morphology, microstructure and the chemical compositions of the core-shell particles were characterized by TEM, XRD and EDX, respectively. The results showed that a compact, continuous and pure spinel structure Co_xFe_3-xO₄ shell was formed on the surface of BaTiO₃ particles after the homogeneous coprecipitation processes at low temperature (<100 °C). The results of vibrating sample magnetometer (VSM) showed that with the R value increasing from 1.5 to 4, the saturation magnetization and coercivity of the BaTiO₃-Co_xFe_3-xO₄ core-shell particles increased from 16.2 emu/g to 38.7 emu/g and 136.6 Oe to 386.5 Oe, respectively. The magnetism of BaTiO₃-Co_xFe_3-xO₄ core-shell particles can be controlled by regulating the R.