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M. Płońska and D. Czekaj

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.

Open access

D. Czekaj, J. Micior and A. Lisińska-Czekaj

Abstract

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 cν =2, 4, 6, 8, 10, 16 and 20 vol. % were prepared. Average grain size of BiNbO4 powder was <d>=1.86 μm. 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 Δν =103-104 Hz. It was found that composite with cν =10% of ceramic powder exhibited lower values of dielectric permittivity.

Open access

D. Czekaj, A. Lisinńska-Czekaj and M. Adamczyk

Abstract

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. Bi2O3 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 ν =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″(ν) spectra) took place at higher frequency than the phenomenon with dominant resistive component (Z″(ν) spectra).

Open access

D. Czekaj and A. Lisińska-Czekaj

Abstract

Bismuth niobate (BiNbO4) has attracted attention as a low-fired ceramics with promising microwave application potential. BiNbO4 ceramics was fabricated by mixed oxide method and sintered at temperature T<1000°C. As the sintering aids a small amount of CuO oxide was used. The crystalline structure of the ceramic samples was examined by X-ray diffraction method at room temperature. The Rietveld refinement method was used for analysis of diffraction data. As a result an influence of dopants on crystal structure of bismuth niobate (BiNbO4) ceramics was revealed. It was found that fabricated BiNbO4 ceramics adopted the orthorhombic symmetry (α-BiNbO4 phase, Pnna (52) space group). Small differences in elementary cell parameters were found.

Open access

B. Wodecka-Duś and D. Czekaj

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 ΔT=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 (Z" vs. Z') as well as simultaneous Bode plots (imaginary parts of impedance Z", admittance Y", electric modulus M" and tanΔ 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.

Open access

D. Czekaj, A. Lisińska-Czekaj, K. Osińska and K. Biernacki

Abstract

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 =8700C and TS =9100C) 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. Bi2O3 and Nb2O5 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 -BiNbO4 phase additional phases, namely tetragonal Bi5Nb3O15, and cubic Bi3NbO7 are possible to form from the mixture of bismuth oxide and niobium oxide. It was found that -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.

Open access

J. Dzik, A. Lisinska-Czekaj, A. Zarycka and D. Czekaj

Abstract

In the present paper studies on Bi1-xNdxFeO3 for x =0.1-0.4 are reported. The mixed oxide method followed with pressureless sintering was employed for ceramics fabrication. Thermal behavior of stoichiometric mixtures of simple oxide powders, viz. Bi2O3, Nd2O3 and Fe2O3 was studied by simultaneous thermal analysis. It was found that with an increase in neodymium content the weight loss increased from 0.75% to 3.16% for x =0.1 and x =0.4, respectively. It was found that weight loss took place mainly within two temperature ranges, namely ΔT1 ≈(300-400)0C and ΔT2 ≈(600-800)°C. Bi1-xNdxFeO3 ceramics was studied in terms of its phase composition (X-ray phase analysis) and chemical composition (EDS method) at room temperature. It was found that Bi1-xNdxFeO3 suffered structural phase transition from rhombohedral to orthorhombic symmetry with an increase in neodymium concentration x within the range x =(0.2-0.3).

Open access

A. Lisińska-Czekaj, D. Czekaj, K. Osińska and M. Adamczyk

Abstract

Goal of the present research was to investigate the influence of V2O5 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 =102-103 Hz and ν =105-106 Hz at temperature T>285°C.

Open access

D. Czekaj, A. Lisińska-czekaj and J. Plewa

Abstract

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.

Open access

B. Wodecka-Duś, M. Plońska and D. Czekaj

Abstract

In the present study BaTiO3 and Ba1-xLaxTiO3 (0.1-0.4mol.% La) ceramic powders were synthesized by the conventional mixed oxide method (MOM). The characterization of the ceramic powders was carried out using a simultaneous thermal analysis (STA), with a combined DTA/TG/DTG system (Netzsch STA409). The results of thermal analysis allowed to determine the optimal temperature of synthesis. Microstructure was investigated by scanning electron microscopy (SEM), crystalline structure was studied by X-ray diffraction method (XRD). The EDS investigations showed that samples exhibited conservation of stoichiometry according to the chemical composition formula. The X-ray diffraction analysis confirmed formation of the desired crystalline structure both pure and La3+-doped BaTiO3 ceramics exhibiting a perovskite-type structure ABO3 with tetragonal symmetry P4 mm.