M. Sokolowski

Influence of uniaxial pressure and aging on dielectric and ferroelectric properties of BaTiO3 ceramics

The effect of uniaxial pressure (0–3000 bar) applied parallel to the AC electric field and aging on dielectric and ferroelectric behavior of BaTiO3 ceramics were investigated. Applying uniaxial pressure leads to a reduction of the peak intensity of the electric permittivity (ε) of the polarization as well as of the dielectric hysteresis. The peak intensity of ε becomes diffused and shifts to a higher temperatures with increasing the pressure. The electrostrictive coefficient Q 11 and differential permittivity were evaluated from the obtained data. We interpreted our results based on the hardening of the soft-mode and domain switching processes under the action of pressure. The aging effect followed a logarithmic law and is related to the relaxation of the domain structure toward an equilibrium configuration. The aging rate was found to decrease with increasing frequency as a result of the pinning of polarization components by defects field.

Effects of PbTiO3 doping on electric properties of Na0.5Bi0.5TiO3 ceramics

ABSTRACT Good quality ceramics of (1−x)Na0.5Bi0.5TiO3(NBT)−xPbTiO3 (PT) (x = 0, 0.03 and 0.05) were prepared by a conventional solid-phase sintering process. The temperature dependence of the dc, ac conductivity ( respectively), the Seebeck coefficient (α), the concentration of charge carriers n and their mobility μ were investigated. The dc conductivity for pure NBT possesses three linear parts with three different activation energies Ea. For 0.97NBT–0.03PT and 0.95NBT--0.05PT ceramics, the dc conductivity also has three linear parts (three different Ea). On the other hand, the ac conductivity possesses three linear parts for pure NBT and four for other compositions. The possible origin of the observed effects is discussed. We suggest that the presented materials can be a good starting point for the development of low-lead electronic ceramics.

Dielectric and ferroelectric properties of 0.82K0.5Bi0.5TiO3-0.18PbTiO3 ceramic: effect of uniaxial pressure

0.82K0.5Bi0.5TiO3-0.18PbTiO3 ceramic was fabricated by the mixed oxide method. An X-ray study shows that the obtained ceramic has a pure perovskite structure. The ϵ(T) and tanδ(T) show a peak centered at about 468 °C and 421 °C, respectively, and related to the tetragonal–cubic phase transition. The effect of uniaxial pressure (0–1500 bar) on dielectric and ferroelectric behavior of this ceramic was investigated. It was shown that uniaxial pressure significantly influences these properties. With the increasing pressure, (1) the maximum value of the electric permittivity and dielectric losses tanδ decreases and increases, respectively, (2) the peaks of ϵ and tanδ shift to higher temperatures, (3) the permittivity characteristics are smeared and the thermal hysteresis decreases, (4) hysteresis loops are smeared. The results were interpreted in term of domains (domains walls) change and de-aging process under the action of uniaxial pressure.

The Influence of Pb(Mg1/3Nb2/3)O3-doping on the thermoelectric properties of BaTiO3 ceramics

ABSTRACT The low-lead (1-x)Pb(Mg1/3Nb2/3)O3-xBaTiO3 (x = 0, 0.025, 0.05, 0.075, 0.10 and 0.15) ceramics were fabricated by a two-step solid-state reaction route. The X-ray diffraction characterization confirms a perovskite crystal structure with tetragonal symmetry at room temperature (except for x = 0.15). SEM images indicate that all ceramic samples are dense and compact, with the grain size of 2–6 μm. Along with the increase of Pb(Mg1/3Nb2/3)O3 content, the electrical conductivity increases, and the Seebeck coefficient and the thermal conductivity decrease. With increasing temperature, σ and α increase and κ decreases. In general, adding Pb(Mg1/3Nb2/3)O3 to BaTiO3 leads to an improvement of the thermoelectric figure of merit ZT. The results are explained on the basis of structural, morphological and compositional changes.

Isothermal depolarization currents of Na0.5Bi0.5TiO3 ceramics

ABSTRACT Na0.5Bi0.5TiO3 ceramics were synthesized by the conventional solid-state reaction method. The influence of polarizing electric field strength, polarization time, and temperature on the depolarization currents of these ceramics was studied. The measurements were made in both the rhombohedral (ferroelectric) and rhombohedral/tetragonal (nonpolar or weakly polar) phases coexistence. The results indicate that depolarization currents follow the Id∼t-s formula. The value of the s parameter depends on the electric field strength, the polarization time, and the temperature. The calculated activation energy is close to that obtained from electric conductivity measurements.

Influence of sintering conditions on structural, thermal, electric and ferroelectric properties of Na0.5Bi0.5TiO3 ceramics

ABSTRACT Na0.5Bi0.5TiO3 ceramics were prepared by a conventional solid-state reaction method and by a hot-pressing route. The influence of sintering conditions on structural, thermal, dielectric and ferroelectric properties of these ceramics was investigated. All obtained samples exhibited a single perovskite phase. It was shown that the sintering conditions significantly influence the properties under investigation. This includes changes in the value of the electric permittivity ϵ and dielectric loss tanδ, a shift of Tm and Td and change of the ferroelectric properties. These effects are mainly related to volatility of the Na and Bi components during the sintering process along with formation of their compensating charge defects, which leads to local structure change.

Dielectric, thermal and ferroelectric properties of Na0.997Li0.003NbO3 ceramics

Na0.997Li0.003NbO3 ceramics of 93% density have been prepared by a solid-state chemical reaction of stoichiometric mixtures of the component oxides and carbonates. The dielectric, thermal expansion, heat capacity, Raman and ferroelectric studies of these ceramics have been performed. The electric permittivity peak shows rather a small dispersion and no change of the maximum position with increasing frequency can be observed. The results clearly show a first-order phase transition at about 375 °C on heating and near 310 °C on cooling and ambiguously indicated another phase transitions. The pyroelectric measurements show for the first time that the material has weak ferroelectric properties, which are rather metastable. The results show that the investigated ceramics are one of the promising lead-free materials for electronic applications.

Pressure Effect on Dielectric Properties of 0.2Na0.5Bi0.5TiO30.8BaTiO3 Ceramics

The dependence of dielectric properties on the uniaxial pressure (0–1500 bar) of 0.2Na0.5Bi0.5TiO3-0.8BaTiO3 ceramic was investigated, revealing a significant influence of the external stress on their properties. This includes a shift of the phase transition, a diffuseness of the permittivity characteristics, a change of the dielectric dispersion and the thermal hysteresis. We discuss our results based on domain/nanoregions switching processes under applying of pressure.

The Uniaxial Pressure Dependence of Dielectric Properties of Na0.5K0.5(Nb0.96Sb0.04)O3+0.5mol%MnO2 Ceramics

The behavior of the electric permittivity and polarization of Na0.5K0.5(Nb0.96Sb0.04)O3+0.5mol%MnO2 ceramics as a function of uniaxial pressure (0 – 600 bar) applied perpendicularly to the ac electric field were investigated. The application of a uniaxial pressure causes a reduction of the peak intensity of the electric permittivity (ɛ) and change of the phase transition from first order to second one. The temperature dependence of electric permittivity ɛ shows that the Curie temperature increases with increasing pressure and presents a broadening and flattening of the maximum of ɛ(T). The obtained results suggested an appearance of the dielectric relaxation near the phase transition temperature which strongly coupled with strain induced by the pressure. The effect of uniaxial pressure have an effect on the dynamics of the perovskite lattice.

Influence of Electromechanical Fields on Dielectric Properties of PLZT−x/65/35 Ceramics (x = 6 and 7)

High density and transparent PLZT−x/65/35 (x = 6 and 7) ceramics with the average grain size of 5–7 μm was obtained by two−stage hot−pressing technology. The measurements of temperature/frequency dependence of the permittivities of these ceramics under uniaxial pressure (0–100 MPa) applied parallel to the ac electric field have been carried out. It was found that uniaxial pressure significantly influences dielectric properties of these ceramics. With the increase of pressure the maximum intensity in ϵ(T) curve decreases, becomes more diffuse and shifts towards higher temperature, dielectric dispersion decreases and classical ferroelectric seems to change to relaxor one. It was concluded, that the applied uniaxial pressure or increasing Ti−ions content in PZT solid solutions induces similar effects. The results were discussed in term of an elastic changes in inter−ionic distances in the crystal structure and domain switching under the action of electromechanical loading.