Thermal behavior of BST//PVDF ceramic–polymer composites

In this paper, we report the results of a study of microstructure and thermal behavior of ceramic–polymer composites composed of barium strontium titanate Ba0.6Sr0.4TiO3 (BST60/40) and polyvinylidene fluoride (PVDF). The Ba0.6Sr0.4TiO3 ceramic powder was prepared by the sol–gel method. Thermal evolution of the dried gel as well as ceramic powder was studied by simultaneous thermal analysis. The composite BST60/40//PVDF was obtained by hot pressing method for volume fraction of BST60/40 ceramic powder c v = 50 %. The morphology of BST60/40//PVDF composite powder was observed by transmission electron microscopy and the morphology of BST60/40//PVDF composite sample was observed by scanning electron microscopy. Temperature dependence of dielectric constant and dielectric loss factor of BST60/40//PVDF composites was measured in the frequency range of f = (10 × 103–1 × 106) Hz. Dynamic mechanical properties of BST60/40//PVDF composites were measured by dynamic mechanical thermal analysis DMTA

Fabrication and Crystal Structure of Sol-Gel Deposited BST Thin Films with Compositional Gradient

In the present research technology of compositionally graded barium strontium titanate Ba1-xSrxTiO3 thin films deposited on stainless steel substrates by sol-gel spin coating followed with thermal annealing at T = 650°C is reported. Results of thermal behavior of the sol-gel derived powders with compositions used for fabrication of graded structure (i.e. with Sr mole fraction x = 0.5, 0.4 and 0.3) are described. X-ray diffraction studies of the phase composition and crystal structure of such complex thin film configuration are given. It was found that gel powders exhibited a large total weight loss of about Δm ≈ 44-47%. Three stages of weight loss took place at temperature ranges: below T ≈ 300°C, at ΔT ≈ 300-500°C and between T = 600°C and T = 800°C. Phase analysis has shown that the dominating phase is Ba0.67Sr0.33TiO3 compound while the second phase is Ba0.7Sr0.3TiO3 or Ba0.5Sr0.5TiO3 for "up-graded" and "down-graded" structure, respectively

A new microwave ceramic - Polymer composite with 0-3 connectivity

Goal of the present research was to fabricate and study two-phase BiNbO4//PVDF composites with 0-3 connectivity. Such composite consists of there-dimensionally connected polymer matrix loaded with dielectric ceramic particles. In the present case BiNbO4 powder acted as an active phase(dispersed phase) whereas polyvinylidene fluoride (PVDF) acted as a non-active (passive) phase (matrix). BiNbO4//PVDF composites with the volume fraction of the ceramic phase cV =2, 4, 6, 8, 10, 16 and 20 vol. % were prepared. Average grain size of BiNbO4 powder was =1.86/m. It was found that BiNbO4 powder exhibited orthorhombic symmetry with Pnna (52) space group and PVDF polymer powder was α-phase. Minimum of dielectric losses at room temperature were found within the frequency range Δv =103-104 Hz. It was found that composite with cV =10% of ceramic powder exhibited lower values of dielectric permittivity

Studies of temperature and fabrication methods influence on structure and microstructure of BiNbO4 microwave electroceramics

The bismuth-based ceramics are well known as potential materials for microwave or microelectronics applications. One of them is a bismuth niobate (BiNbO4), which belongs to the family of the scheelite-like stibiotantalite structure A3+B5+O4. This low temperature co-fired dielectric ceramics is also reported as a good microwave dielectric material, using i.e. in multilayer microwaves systems. In the present studies depends of fabrication methods and temperature conditions on basic properties of bulk BiNbO4 are reported. Technological process included two stages. First, the ceramic powder was obtained from the high purity oxides (99.99%), by MOM method. The second stage involved consolidation of such prepared powders by free sintering and the hot uniaxial pressing methods. Goal of this study was to investigate how the fabrication processes i.e. temperature and sintering conditions influence on prepared powders and samples of bismuth niobate, like its structure and microstructure

Dielectric properties of bismuth ferrite-bismuth titanate ceramic composite

In this paper the BiFeO3//Bi4Ti3O12 (BF//BiT) ceramic-ceramic composites with 0-3 connectivity were prepared from BiFeO3 and Bi4Ti3O12 ceramic powders by free sintering method at T=900 C, for different concentration of the BF ceramic phases. Bi4Ti3O12 and BiFeO3 ceramic powders were synthesized by the conventional mixed oxide method (MOM). Synthesized BF powder was dispersed in a BiT solution and next such composite was pressing and sintering. Crystalline structure was studied by X-ray diffraction method. The dielectric properties of the BF//BiT ceramic composites were also investigated. Temperature dependence of dielectric permittivity of BF//BiT composites was measured in the frequency range of f =10kHz-100kHz. It was found, that properties of the ceramic-ceramic composite are not a simple sum of properties of the phases constituting the composite but they depend on both the way of connectivity and mutual influence of the phases on each other. The abrupt increase in permittivity may indicate an excess of the percolation threshold, so the ceramic composite for the concentrations of the BF ceramic phase cV >10% cannot be indexed as composites with 0-3 connectivity

Influence of bismuth content on complex immittance characteristics of pressureless sintered BiNbO4 ceramics

Goal of the present research was to study immittance properties of BiNbO4 ceramics fabricated by the solid state reaction route followed by pressureless sintering. Four sets of samples were examined, namely the one fabricated from the stoichiometric mixture of oxides, viz. Bi2O 3 and Nb2O5 as well as the ones with an excess of 3%, 5% and 10% by mole of Bi2O3. The immittance properties were studied by impedance spectroscopy. Measurements were carried out within the frequency range T =20Hz-1MHz and temperature range T =RT-550°C. The Kramers-Kronig data validation test was employed in the impedance data analysis. It was found that complex impedance first increases with an increase in Bi2O3 content and decreases for 10mol% excess of Bi2O3. Two relaxation phenomena manifested themselves at elevated temperature (T >267°C) within the measuring frequency range. The conductivity relaxation phenomenon (M′′(v) spectra) took place at higher frequency than the phenomenon with dominant resistive component (Z′′(v) spectra)

Effect of Bi2O3 excess on morphology and structure of BiNbO4 ceramics

Goal of the present research was to fabricate BiNbO4 ceramics from the mixture of powders by the solid state reaction route and pressureless sintering at various temperatures (Ts =870°C and Ts =910°C) and study microstructure, phase composition and crystalline structure of BiNbO4 ceramics. Four batches were fabricated and examined, namely the one fabricated from the stoichiometric mixture of reagent - grade oxide powders, viz. Bi203 and Nb20 5 as well as the ones with an excess of 3%, 5% and 10% by mole of Bi2O3. It was found that apart from the main orthorhombic a-BiNb04 phase additional phases, namely tetragonal Bi 5Nb3015, and cubic Bi3NbO 7 are possible to form from the mixture of bismuth oxide and niobium oxide. It was found that α-BiNbO4 ceramics exhibited the orthorhombic symmetry identified as Pnna (52). However, small differences in elementary cell parameters were found for the samples sintered from stoichiometric and non-stoichiometric mixture of initial powders

Synthesis of 0.7BiFeO3-0.3BaTiO3 ceramics : thermal, structural and AC impedance studies

In a present paper results of the process of synthesis and study of a perovskite-type solid solution of the chemical composition (1-x)BiFeO3–xBaTiO3 for x=0.3 are reported. Synthesis of 0.7BiFeO3–0.3BaTiO3 (BF–BT) ceramics was carried out according to the solid-phase reaction from the mixture of powders. Simultaneous thermal analysis (STA) and X-ray diffraction method were utilized to study the synthesis of BF–BT ceramics. On the basis of STA analysis the optimum conditions of the thermal treatment were found. BF–BT ceramics was studied in terms of its microstructure (SEM), chemical composition (EDS), crystalline structure (XRD), and dielectric properties (impedance spectroscopy) at room temperature. It was found that dense BF–BT ceramics with a cubic structure of Pm3m space group and desired stoichiometry ( 3%) was fabricated under technological conditions differing in both sintering temperature (T=750 C–850 C) and soaking time (t=2h-40h). It was found that an increase in sintering temperature for T=100 C made it possible to decrease the soaking time 10 times. Impedance spectroscopy was utilized for characterizing dynamical dielectric properties of 0.7BF–0.3BT ceramics. The alternative representation of impedance data in a form of complex plot (Z00 vs. Z0) as well as simultaneous Bode plots (imaginary parts of impedance Z00, admittance Y00, electric modulus M00 and tan versus frequency in a log-log scale) were used for preliminary visual analysis. Kramers-Kronig transform test was utilized for experimental data validation. To analyze the room temperature impedance spectroscopy data complex nonlinear least squares fitting method was used and the data were fitted to the corresponding equivalent circuit consisting of resistors and constant phase elements. Agreement between experimental and simulated data was established

Fabrication, structural and AC impedance studies of layer-structural Bi4Ti3O12 ceramics

In the present research bismuth titanate Bi4Ti3O12 (BiT) ceramics was synthesized by the standard solid-state reaction method from the mixture of oxides, followed by free sintering at temperature T=1000 C. BiT ceramics was studied in terms of its chemical composition (EDS), crystalline structure (X-ray), microstructure (SEM) and dielectric properties (ac technique of complex impedance spectroscopy) over a range of frequency ( f =100Hz to f =1MHz) and temperature (T=200-500 C). Experimental results confirmed the phase formation. It was found that BiT ceramics crystallized in orthorhombic symmetry, best described with Fmmm space group and the following elementary cell parameters: a=5.409(6)°A, b=5.449(2)°A and c=32.816(2)°A. It was also found that BiT ceramics exhibited the plate–like microstructure and stoichiometric chemical composition. Impedance spectroscopy measurements showed contribution of three overlapping relaxation processes (three semicircles in the complex impedance diagrams were observed) ascribed to bulk, grain boundary and electrode/interface polarization phenomena. Impedance data were fitted to the corresponding equivalent circuit using the complex nonlinear least squares (CNLS) method. The ac conductivity for grains, grain boundaries and electrode processes was calculated from CNLS fit of the impedance data and thus the activation energy of ac conductivity ( AC) and relaxation ( ) was calculated for the three revealed components of the impedance spectra from the slopes of AC and versus 1000/T plots (semi log scale) in the range of T=200–500 C

Wpływ V2O5 na strukturę i właściwości dielektryczne ceramiki BiNbO4

Goal of the present research was to investigate the influence of V 2O5 additive on the structure and dielectric properties of BiNbO4 ceramics. To fabricate BiNbO4 ceramics with V2O5 added the solid state reaction route and pressureless sintering was utilized. Thus obtained ceramics was characterized in terms of its microstructure (SEM), chemical composition (EDS), phase composition and crystalline structure (X-ray phase and structural analysis, respectively). Also dielectric properties in both temperature and frequency domains were investigated. The impedance spectroscopy was utilized for dielectric characterization and the measurements of complex impedance were performed within the frequency range ν =10Hz-1MHz and temperature range T =RT-550°C. It was found that V2O5 additive changed slightly lattice parameters of BiNbO4 ceramics, decreased porosity of samples and revealled relaxation phenomena within the frequency ranges ν =102-103Hz and ν =105-106Hz at temperature T>285°C