M. Adamczyk

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.

Influence of sintering conditions on relaxor properties of BaBi2Nb2O9 ceramics

The main purpose of present studies is to learn the effect of sintering temperature on BaBi2Nb2O9 (BBN) ceramics properties. Grain structure analysis performed by the scanning electron microscope (SEM) exhibits differences in grain structure of the ceramics sintered at various temperatures for a constant time. Namely, the grain sizes increase with the increase of the sintering temperature. This fact is connected with changes in dielectric properties. The maximum of the real part of permittivity ( ) and corresponding temperature (T m) shifts to higher values. The properties characteristic for the ferroelectric relaxors also yield to change. The ceramics sintered in higher temperature revealed lower frequency dispersion of and T m. It should also be noticed that the freezing temperature and the Burns temperature have changed. These results indicate that the behaviour of the relaxor ferroelectrics is weakened by the increase in the grain size.

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.

Dielectric properties of neodymium-modified PLZT ceramics

Relaxor ferroelectrics or relaxors are a class of disordered single crystals and ceramic materials, of peculiar structure as well as properties. The commonly known examples of such materials are Pb(Mg,Nb)O3 (PMN) ceramics as well as single crystals. The second most extensively studied relaxor ceramics is lanthanum-doped lead zirconate–titanate, described as x/65/35 PLZT when lanthanum content is x = 6–10 at%. Throughout the last few decades, there has been an increasing interest in rare-earth-doped PLZT ceramics, because PLZT can be easily substituted with lanthanide elements for La3+ ions. For this reason, the present studies concern the changes in microstructure and crystal structure as well as in dielectric properties, caused by modification of 8/65/35 PLZT with neodymium dopant. Modification of this material with Nd3+ influences the microstructure, electrooptical and dielectric properties, whereas the changes in crystal structure are slight. It was also observed that the maximum value of dielectric properties decreases and moves to a low temperature. Described changes in physical properties are associated with the significant improvement of relaxor properties, characteristic for pure 8/65/35 PLZT ceramics.

Impedance Spectroscopy of BaBi2Nb2O9 Ceramics

Investigations presented in the present work are concerning the other member of the Aurivillius family, the BaBi2Nb2O9 (BBN). This compound, which seems to be very interesting from the potential applications point of view. The dielectric characterization of this materials and influence of sintering condition on grain structure and properties of those materials had been very widely described in our previous paper. Now we would like to present the hitherto unreported electric properties of BaBi2Nb2O9 ceramics, investigated by the impedance spectroscopy (IS). IS is nondestructive method, which allows to separate grain and grain – boundary effects due to the different frequencies of the relaxation process in grain and grain boundaries. This enables us to determine the temperature dependences of grain (Rg) and grain-boundary (Rgb) resistance and evaluate their respective activation energies (Ea). Additionally a comparison between macroscopic results obtained by Impedance Spectroscopy and miroscopic direct local LC-AFM conductivity measurements are presented.

Relaxor properties of Nb-modified (Ba0.8Sr0.2)TiO3 ceramics

Nb-doped (Ba0.8Sr0.2)TiO3 ceramics were prepared using conventional mixed-oxide processing technique. Permittivity and loss factor were investigated as a function of temperature for various frequencies of the measuring field. The obtained results confirmed the relaxor ferroelectric behaviour of the studied ceramics, i.e. a strong frequency dispersion of the permittivity maximum and a visible shift of its temperature with frequency. Analysis of real part of permittivity allowed us to determine the value of the freezing temperature characterising the relaxor ferroelectrics. The physical processes, responsible for the relaxor behaviour of the studied ceramics are discussed.

Influence of post-sintering annealing on relaxor properties of BaBi2Nb2O9 ceramics

The effect of thermal treatment on the properties of Bi-layered ceramics, and particularly of the BaBi2Nb2O9 ceramics was considered to be marginal, despite the fact that their dielectric and relaxor properties are strongly related to the degree of heterogeneity. The aim of this article is to determine the influence of defects, especially the concentration of oxygen vacancies, on the relaxor properties of BaBi2Nb2O9. The results show that the oxygenation, taking place in the first phase of post-sintering annealing, do not affect significantly the values of the parameters characteristic of ferroelectric relaxors. The parameters undergo changes only after prolonged annealing, when the content of barium and bismuth were slightly changed.

Mechanical properties of BaBi2Nb2O9 ceramics obtained by different measurements techniques

Gaining the precise control over the matter at the nanometre scale is the main leitmotif in a majority of nanoscience oriented research measurements nowadays. The availability of new advanced tools, as a nanoindentation technique, for evaluation of the mechanical properties, seems to be prerequisite for exploitation of the dramatic development in nanoscience and meeting the emerging needs of the industries in new electronic applications. The nanoindentation technique was applied to evaluate the elastic modulus and hardness values as a function of indentation depth. However, in the presented experiment the nanoscale mechanical properties of BaBi2Nb2O9 ceramics have been characterized and compared with the macroscale measurements with macroscale method with the implementation of ultrasound techniques. A draw conclusion indicates that expensive nanoscale characterisation presented here is not fully consisted with the microscale. The reasons of such state of things are widely discussed.

Technology of PLZT ceramics microfibers for multiferroics composites

Compactness and large energy conversion capacity are the main reasons of development of sophisticated ceramics materials in microfibers form, which are prepared for high-speed multiferroic systems and devices. These multifunctional composite applications are owing to coupling of electrical and magnetic properties, as well as additional thermal and mechanical properties. So that, they are suitable for magnetic sensors, electrically tunable non-linear transducers, and non-volatile memories. In our experiment, the thin fibers ceramics have been produced using special environmental chamber where the high temperature sintering can be protected by controlling such parameters as temperature and sintering atmosphere. Consequently, for these purposes structural and physical properties, preparation and thermal synthesis of micrometer sized lead lanthanum zirconate titanate (PLZT) fibers were investigated thoroughly. Since the phase transition properties of PLZT fibers differ much, the production process of fibers suffers from lack of proper high temperature control. Consequently, our experiments should help to eliminate this drawback, so that various technological conditions, parameters, and subsequent sintering atmosphere with different mixtures of PbO and ZrO were experimentally tested. Final conclusions include comparative analysis of obtained PLZT fibers ferroelectric phase transition properties to specific sintering atmosphere.

Effect of Sr doping on phase transition and electric behaviour of (Pb0.70Sr0.30)(Zr0.70Ti0.30)O3 ceramics

The ferroelectric (FE) materials are continuously attracting considerable attention due to the interesting combination of their mechanical, electrical and chemical properties and their application in microelectromechanical devices (piezoelectric transformers, motors and transducers). To be more specific, their excellent electrostrictive properties coupled with domain mobility, high Curie point and good stability make these ‘new materials’ important components of electroceramic devices. It is already known that the electrical behaviour of these FE materials largely depends on random elasto-electric fields connected with the diffusion of phase transition and defects distribution. The aim of this article is the exposition of phase transition dependence on Sr2+ homovalent dopant in (Pb0.70Sr0.30)(Zr0.70Ti0.30)O3 ceramics investigated by electrical methods. We demonstrate that electrical examination can be effectively used for drawing decisive applications conclusions from the grain and grain boundary parameters distribution. Modification of FE materials with isovalent ions, but with radii bigger than the original atom, significantly affect its properties, particularly the (Pb,Sr)(Zr,Ti) O3 real part of electrical permittivity shows the change of phase transition from FE to relaxor.