Dionizy Czekaj

Synthesis and dielectric properties of Am-1Bi2BmO3m+3 ceramic ferroelectrics with m=1.5

Abstract Bismuth containing ceramic materials of molecular formula Bi 5 TiWNbO 15 , Bi 5 Ti 1/2 W 1/2 Nb 2 O 15 , Bi 5 Nb 3 O 15 have been synthesised and fabricated. The materials are known as the Aurivillius phases. The Aurivillius phases are a family of oxide ferroelectrics generally formulated as A m −1 Bi 2 B m O 3 m +3 . The process of preparation was investigated by X-ray diffraction method as well as the simultaneous thermal analysis, in which both thermal (DTA) and mass change effects (TG) were measured on the same sample. The synthesis of the Aurivillius phases was carried out according to the solid state reaction from the conventional mixture of oxides (Nb 2 O 5 , WO 3 , Bi 2 O 3 , and TiO 2 ). DTA and TG traces showing the synthesis effects have been recorded. Investigations of the crystalline structure, microstructure and basic dielectric properties were performed.

Structure and dielectric properties of PZT-type ceramics with the diffuse phase transition

In the present work the (Pb0.84Ba0.16)(Zr0.54Ti0.46)O3 (PBZT) solid solution has been synthesized. The process of preparation was investigated by simultaneous thermal analysis (STA) and X-ray diffraction method. The hot pressing method was utilized for densification of ceramic samples. Dielectric properties of donor- and acceptor-doped PZT-type ceramics were measured within the temperature range including the phase transition region. Frequency-dependent relaxation behaviour in PBZT ceramics was found. The structural phase transition at T = (517 ± 3) K was determined by X-ray diffraction method. Arrhenius plot of total conductivity derived from ac impedance spectroscopy measurements was used for characterisation of phase transition. Changes in activation energy were found characteristic of phase transition in PBZT ceramics.

Fabrication and Study of BiNbO4 Ceramics

Aim of the present research was to fabricate and study crystalline structure as well as dielectric properties of BiNbO4 ceramics. In the present study BiNbO4 ceramics was fabricated by solid state reaction from the mixture of simple oxides viz. Bi2O3, and Nb2O5. Stoichiometric mixture of the powders was thermally analyzed so parameters of the thermal treatment were determined. The EDS measurements proved conservation of the chemical composition of the ceramic powder after calcination (T=800°C). Free sintering at T=870 – 1080 °C was used for fabrication of the ceramic samples. Morphological analysis using scanning electron microscopy was performed. The crystalline structure of the sintered samples were examined by X-ray diffraction method at room temperature. It was found that for low temperature of sintering (T0C) bismuth niobate crystallized in orthorhombic symmetry Pnna (52) whereas for high sintering temperature (T>1000 °C) BiNbO4 exhibited anorthic symmetry P-1 (2). Low frequency (ν=100Hz – 1MHz) impedance spectroscopy was applied to study influence of the sintering temperature on dielectric properties of bismuth niobate at room temperature. The equivalent circuit method was used for analysis of the impedance data.

Comparative X-ray diffraction and Mössbauer spectroscopy studies of BiFeO3 ceramics prepared by conventional solid-state reaction and mechanical activation

The aim of this work was to prepare BiFeO3 by modified solid-state sintering and mechanical activation processes and to investigate the structure and hyperfine interactions of the material. X-ray diffraction and Mössbauer spectroscopy were applied as complementary methods. In the case of sintering, BiFeO3 phase was obtained from the mixture of precursors with 3 and 5 % excess of Bi2O3 during heating at 1023 K. Small amounts of impurities such as Bi2Fe4O9 and sillenite were recognized. In the case of mechanical activation, the milling of stoichiometric amounts of Bi2O3 and Fe2O3 followed by isothermal annealing at 973 K resulted in formation of the mixture of BiFeO3, Bi2Fe4O9, sillenite and hematite. After separate milling of individual Bi2O3 and Fe2O3 powders, mixing, further milling and thermal processing, the amount of desired BiFeO3 pure phase was significantly increased (from 70 to 90 %, as roughly estimated). From Mössbauer spectra, the hyperfine interaction parameters of the desired BiFeO3 compound, paramagnetic impurities of Bi2Fe4O9 and sillenite were determined. The main conclusion is that the lowest amount of impurities was obtained for BiFeO3 with 3 % excess of Bi2O3, which was sintered at 1023 K. However, in the case of mechanical activation, the pure phase formed at a temperature by 50 K lower as compared to solid-state sintering temperature. X-ray diffraction and Mössbauer spectroscopy revealed that for both sintered and mechanically activated BiFeO3 compounds, thermal treatment at elevated temperature led to a partial eliminating of the paramagnetic impurities.

Dielectric, Pyroelectric and Thermally Stimulated Depolarization Current Investigations on (Ba, Sr)TiO3 Ceramics with Bi2O3 Additive

The Ba1−x Sr x TiO3 materials have received increased attention as one of the most important materials for electroceramic components, such as high dielectric ceramic capacitors, tunable phase shifters and PTCR. In this paper the effect of 0.5; 1; 1.5; and 2 mole% of Bi2O3 addition on microstructure, structure, dielectric properties (i.e., dielectric constant ϵ′, and dielectric loss factor tan δ), as well as pyroelectric and thermally stimulated depolarization currents (TSDC) of (Ba0.8Sr0.2)TiO3 ceramics have been investigated. The distinct correlation between Bi2O3 content, wide maxima in TSDC, anomalies in ϵ′ (T) and tan δ (T) characteristics occurring within the range of the paraelectric phase was confirmed. Changes of electric conductivity and Seebecks coefficient, caused by Bi2O3-additives, were also studied.

Structure and some magnetic properties of (BiFeO3)x-(BaTiO3)1−x solid solutions prepared by solid-state sintering

Abstract This paper presents the results of the study on structure and magnetic properties of the perovskite-type (BiFeO3)x-(BaTiO3)1−x solid solutions. The samples differing in the chemical composition (x = 0.9, 0.8, and 0.7) were produced according to the conventional solid-state sintering method from the mixture of powders. Moreover, three different variants of the fabrication process differing in the temperatures and soaking time were applied. The results of X-ray diffraction (XRD), Mössbauer spectroscopy (MS), and vibrating sample magnetometry (VSM) were collected and compared for the set of the investigated materials. The structural transformation from rhombohedral to cubic symmetry was observed for the samples with x = 0.7. With increasing of BaTiO3 concentration Mössbauer spectra become broadened reflecting various configurations of atoms around 57Fe probes. Moreover, gradual decreasing of the average hyperfine magnetic field and macroscopic magnetization were observed with x decreasing.

Magnetoelectric effect in (BiFeO3)x–(BaTiO3)1-x solid solutions

Abstract The aim of the present work was to study magnetoelectric effect (ME) in (BiFeO3)x-(BaTiO3)1-x solid solutions in terms of technological conditions applied in the samples fabrication process. The rapidly growing interest in these materials is caused by their multiferroic behaviour, i.e. coexistence of both electric and magnetic ordering. It creates possibility for many innovative applications, e.g. in steering the magnetic memory by electric field and vice versa. The investigated samples of various chemical compositions (i.e. x = 0.7, 0.8 and 0.9) were prepared by the solid-state sintering method under three sets of technological conditions differing in the applied temperature and soaking time. Measurements of the magnetoelectric voltage coefficient αME were performed using a dynamic lock-in technique. The highest value of αME was observed for 0.7BiFeO3-0.3BaTiO3 solid solution sintered at the highest temperature (T = 1153 K) after initial electrical poling despite that the soaking time was reduced 10 times in this case.

INFLUENCE OF Mg-DOPING ON SYNTHESIS OF SOL–GEL DERIVED BST THIN FILMS

Solid solutions of Ba1-xSrxTiO3 (BST) type are very attractive for application in information technology, but also in microwaves for such electrically controlled devices as phase shifters, tunable filters, steerable antennas, varactors, etc. In the present study thin films of a BST solid solution with x = 0.4 (BST60/40) were prepared by the sol–gel-type chemical solution deposition method. The influence of y = 1, 3 and 5 mol.% MgO doping on synthesis of BST60/40 thin films was studied. Thermal analysis both differential and thermogravimetric were used to determine the thermochemical properties of dried BST60/40–MgO gel powders. A multilayer spin-coating approach was utilized for the Ba0.6Sr0.4TiO3–MgO thin film deposition on stainless steel substrates. X-ray diffraction analysis, SEM and EDS were utilized for thin film characterization in terms of its crystalline structure, microstructure and chemical composition. Raman spectroscopy investigation of MgO-doped Ba0.6Sr0.4TiO3 thin films grown on stainless steel substrates were also performed within the wavenumber range k = 40–1070 cm-1.

Piezoceramic Transducers with High Thermal Stability of the Resonance Frequency

Methods for increasing thermal stability of the resonance frequency f r of the PZT-based piezoceramic resonators are shown. An influence of ( x )PbTiO 3 content and an effect of doping ions on j f r / f r in the PZT solid solution has been considered. Correlation between qualities of the domain structure, spontaneous deformation parameters i T , i Re , degree of domain reorientation m , internal friction Q m m 1 and mechanical quality factor Q m , has been revealed. An impact of electronegativity of the doping ions on f r thermal stability have been cleared up. Ferroelectric hardness has also been considered. The piezoceramic band filters exhibiting j f r / f r <0.2% and Q m =3225 have been thus obtained.

Mössbauer Spectroscopy and Magnetoelectric Effect Studies of Multiferroic Ceramics Based on BiFeO3

In this work the results of investigations for (BiFeO3)x(BaTiO3)1-x and Bi1-xNdxFeO3 solid solutions are described. Samples were prepared by the conventional solid-state sintering method. X-ray diffraction, 57Fe Mössbauer spectroscopy, and magnetoelectric effect measurements were applied as complementary methods to determine the structure and magnetic properties of materials. For (BiFeO3)x(BaTiO3)1-x solid solutions Mössbauer spectroscopy revealed the relationship between the content of BiFeO3 and the magnetic properties of the samples. Moreover, the presence of magnetoelectric coupling in (BiFeO3)x(BaTiO3)1-x solid solutions was registered at room temperature for the materials sintered at various temperatures. The maximum value of magnetoelectric voltage coefficient was achieved for 0.7(BiFeO3)0.3(BaTiO3) sintered at 1153K. Structure of Bi1-xNdxFeO3 solid solutions was investigated in the whole range of concentration. Hyperfine interactions parameters were determined for the first time for these solid solutions.