BFN Powder Research Articles

Mechanochemical Activation and Spark Plasma Sintering of the Lead-Free Ba(Fe1/2Nb1/2)O3 Ceramics.

This paper investigates the impact of the technological process (Mechanochemical Activation (MA) of the powder in combination with the Spark Plasma Sintering (SPS) method) on the final properties of lead-free Ba(Fe1/2Nb1/2)O3 (BFN) ceramic materials. The BFN powders were obtained for different MA duration times (x from 10 to 100 h). The mechanically activated BFN powders were used in the technological process of the BFN ceramics by the SPS method. The measurements of the BFNxMA ceramic samples included the following analysis: Scanning Electron Microscopy (SEM), Energy Dispersive Spectrometry (EDS), DC electrical conductivity, and dielectric properties. X-ray diffractions (XRD) tests showed the appearance of the perovskite phase of BFN powders after 10 h of milling time. The longer milling time (up 20 h) causes the amount of the perovskite phase to gradually increase, and the diffraction peaks are more clearly visible. Short high energy milling times favor a large heterogeneity of the grain shape and size. Increasing the MA milling time to 40 h significantly improves the microstructure of BFN ceramics sintered in the SPS technology. The microstructure becomes fine-grained with clearly visible grain boundaries and higher grain size uniformity. Temperature measurements of the BFN ceramics show a number of interesting dielectric properties, i.e., high values of electric permittivity, relaxation properties with a diffusion phase transition, as well as negative values of dielectric properties occurring at high temperatures. The high electric permittivity values predestines the BFNxMA materials for energy storage applications e.g., high energy density batteries, while the negative values of dielectric properties can be used for shield elements against the electromagnetic radiation.

The size-matching effect in 0.1Na 1/3 Ca 1/3 Bi 1/3 Cu 3 Ti 4 O 12 - x Ba(Fe 0.5 Nb 0.5 )O 3 -(0.9- x )PVDF composites

Abstract High discharged energy density polymer composites are quite promising for capacitors and many other electronic devices. In this study, nano-sized Ba(Fe 0.5 Nb 0.5 )O 3 (BFN) powders and micro-sized Na 1/3 Ca 1/3 Bi 1/3 Cu 3 Ti 4 O 12 (NCBCTO) powders are embedded in 3-dimensionally connected poly(vinylidene fluoride) (PVDF) matrix, which has the potential to combine the high breakdown strength of the polymer with the high dielectric constant of the ceramics. The three-phase 0.1Na 1/3 Ca 1/3 Bi 1/3 Cu 3 Ti 4 O 12 - x Ba(Fe 0.5 Nb 0.5 )O 3 -(0.9- x )PVDF composites were obtained by physical mixing, cold press technique and heat treatment. The dielectric permittivity of the composites is as high as 38.96 at 100 Hz when the value of x is 0.20. A large discharged energy density of 1.45 J cm −3 is achieved at a field of 600 kV/cm for the composites when the value of x is 0.05, which is attributed to the size-matching effect. The dense composites can be obtained when the hole defects between micro-sized NCBCTO powders and PVDF are filled with part of nano-sized BFN powders.

Preparation and dielectric properties of the lead-free BaFe1/2Nb1/2O3 ceramics obtained from mechanically triggered powder

In the paper the influence of mechanical activation of the powder on the final dielectric properties lead-free Ba(Fe1/2Nb1/2)O3 (BFN) ceramic was examined. The BFN ceramics were obtained by 3-steps route. Firstly, the substrates were pre-homogenized in a planetary ball mill. Than, the powder was activated in vibratory mill (the shaker type SPEX 8000 Mixer Mill) for different duration between 25 h and 100 h. The influence of the milling time on the BFN powder was monitored by X-ray diffraction. The diffraction data confirmed that the milling process of the starting components is accompanied by partial synthesis of the BFN materials. The longer of the high-energy milling duration the powders results in increasing the amount of amorphous/nanocrystalline content. The mechanically activated materials were sintered in order to obtain the ceramic samples. During this temperature treatment the final crystallisation of the powder appeared what was confirmed by XRD studies. The performed dielectric measurements have revealed the reduction of the dielectric loss of the BFN ceramics compared to materials obtained by classic methods.

Excellent stability and low dielectric loss of Ba(Fe0.5Nb0.5)O3 synthesized by a solution precipitation method

A solution precipitation method was applied to prepare Ba(Fe0.5Nb0.5)O3 powders. Nano-size BFN powders with uniform particles size (∼40 nm) were synthesized by solution precipitation method, which is beneficial to calcine at low temperature (1223 K). The sintering sample with dense microstructure and uniform grain size (15 μm) was obtained at 1673 K, which exhibits enhanced dielectric properties. The dielectric loss of BFN ceramic could be significantly reduced by solution precipitation method. The frequency and temperature stability of BFN ceramics could also be improved. The complex impedance spectroscopy analysis results suggested that the obtained Ba(Fe0.5Nb0.5)O3 ceramics, consisting of semiconducting grains and insulating grain boundaries, were electrically heterogeneous. The grain boundary effect was responsible for such a high value of dielectric constant.

Structure and Dielectric Properties of Lead-Free BaSn0.1Ti0.9O3-BaFe0.5Nb0.5O3 Ceramics

Binary solid solutions of the (1-x)BaSn0.1Ti0.9O3-xBaFe0.5Nb0.5O3 system, with x = 0, 0.05, 0.10, 0.15 and 0.20 were prepared via a solid-state processing technique. The BST and BFN powders were synthesized separately using a calcination technique with optimum temperature. XRD results revealed that the structures of the BST-BFN ceramics were of tetragonal symmetry and the tetragonality (c/a ratio) decreased with increasing BFN content. BFN caused enhanced dielectric constant of BST ceramics that increased with temperature. The highest dielectric constant was ∼120000 for x = 0.20 at temperature of 400°C (1 kHz).

Magnetic and electric properties of the lead free ceramic composite based on the BFN and ferrite powders

Ferroelectromagnetic BaFe0.5Nb0.5O3 (BFN) ceramics and ferroelectromagnetic composites based on BFN powder and ferrite powder have been obtained in the presented work. The percentage of components in a two-phase composite was: biferroic powder BFN in the amount of 90%, and nickel–zinc ferrite Ni1−xZnxFe2O4 for x=0.36 in the amount of 10%. The synthesis of the components of the BFN–ferrite composite was performed using the calcination method. Final densification of the synthesized powder was done using free sintering.For the obtained two-phase ceramic BFN–ferrite composite, the XRD, microstructure, EDS, dielectric, impedances, magnetic, Mössbauer and electrical hysteresis loop investigations were performed. The obtained results show correlations between the magnetic subsystem and the electrical subsystem of the ferroelectromagnetic composite. Such properties of the obtained composite give a possibility to use them in memory applications of a new type.

Effects of GeO2 addition on physical and electrical properties of BaFe0.5Nb0.5O3 ceramic

This paper presents the effect of GeO2 glass former on the physical and electrical properties of BaFe0.5Nb0.5O3 (BFN) perovskite ceramics. The BFN powder was prepared by a conventional mixed-oxide method and the GeO2 contents, ranging from 1 to 5wt.%, were subsequently added to the calcined BFN powder. The mixtures were pressed and sintered to form dense ceramics. We showed that, with the addition of GeO2, the maximum density was achieved at lower sintering temperature, approximately 200–225°C lower than those required by the pure BFN ceramic. However, the densities of these GeO2 doped BFN ceramics were slightly lower than those of pure BFN due to the occurrence of pores. We also found that the addition of GeO2 reduces the dielectric loss at room temperature from 4.29 to 0.39–0.79 but the dielectric constant at room temperature decreased with the increased GeO2 concentrations. With small amount of added GeO2, ferroelectric property of BFN ceramics was also obtained, as confirmed by their hysteresis loops.

Microstructure and Electrical Properties of BaFe0.5Nb0.5O3 Doped with GeO2 (1–5 wt.%)

In this work, the effects of GeO2 dopant on the electrical properties of BaFe0.5Nb0.5O3 (BFN) perovskite ceramics were investigated. The BFN powder was prepared by a conventional mixed-oxide method using stoichiometric amounts of BaCO3, Fe2O3 and Nb2O5. Afterward the GeO2 contents, ranging from 1 to 5 wt.%, were added to the calcined BFN powder and mixed via vibro-milling method. The mixtures were pressed and sintered at 1125–1150°C for 4 h to form dense ceramics. We showed that the addition of GeO2 caused a reduction of grain size and formation of secondary phases: Ba3Fe2Ge4O14 and BaGeO3. The maximum densities of these BFN doped with GeO2 ceramics were slightly lower than those of the pure BFN due to the occurrence of pores. We also found that the GeO2 doping could improve the dielectric properties of these ceramics at room temperature (25°C). The 1 wt.% GeO2 doped sample exhibited higher dielectric constant of about 1800 and lower dielectric loss of 0.45 comparing to that of pure BFN. However, the dielectric constant values of these ceramics at high temperature (>25°C) were decreased significantly with the increase of GeO2 concentration. In addition, the GeO2 additive gave a weak ferroelectric behavior, leading to change in the pyroelectric coefficient and spontaneous polarization of the GeO2 doped BFN ceramics.

Microwave synthesis of barium iron niobate and dielectric properties

A microwave synthesis was applied to prepare barium iron niobate (BFN) powders for the first time. Pure perovskite phase of BFN with a cubic symmetry was obtained when precursors were calcined at 850 °C for 14 h. Average particle size of pure BFN powder was estimated to be in submicron range. The examination of dielectric spectra indicated that BFN ceramics prepared by the present method exhibited rather high dielectric constant (∼ 30,000 at 300 °C for 1 kHz) with low dielectric loss (less than 0.6).

Effect of ZrO<sub>2</sub> Doping in Physical Properties of Barium Iron Niobate Ceramics

In this work, preparation conditions and effect of ZrO2 doped BaFe0.5Nb0.5O3 ceramics were studied. Relationship between structure and dielectric properties was investigated. Single-phase cubic BFN powder was synthesized by solid-state reaction at 1200°C for 4 hours with heating and cooling rate of 5°C/min. Various amount of ZrO2 doped from 0.1 to 0.5 %weight were used for doping. After that BFN ceramics were formed via uniaxial pressing and sintered at 1300°C for 4 hours with heating and cooling rate of 5°C/min. Physical properties, microstructure, phase evolution and dielectric properties were studied to find out the optimum conditions for high voltage capacitor applications.

Preparation and characterization of barium iron niobate (BaFe0.5Nb0.5O3) ceramics

Abstract Barium iron niobate (BaFe 0.5 Nb 0.5 O 3 : BFN) is a relaxor ferroelectric material that has a diffuse phase transition (DPT) with a broad maximum in the temperature dependence of the dielectric constant. This ceramic is useful for high voltage capacitors and other applications. In this research, ceramic powder of BFN was synthesized by the solid state reaction technique and calcined at 800–1200 °C for 4 h with 5 °C/min heating and cooling rate. The phase identification of calcined powders was performed using X-ray diffraction technique (XRD). The XRD patterns show that pure cubic BFN powder could be obtained at 1200 °C. The powder was then pressed into disc shape which was subsequently sintered at 1250–1400 °C for 4 h with 5 °C/min heating and cooling rate. Densities of the sintered discs were determined by Archimedes principle. The microstructure of the ceramics was examined by the scanning electron microscopy (SEM). The temperature dependence of dielectric constant was presented.