W. Smiga

Electrical Properties of Na 0.98 Li 0.02 NbO 3 Under Axial Pressure in Phase Transition Region

The measurements of electric properties of Na 0.98 Li 0.02 NbO 3 ceramics for stress-free or samples under stress have been carried out. It was found that incorporation of Li-cations (2% mol) in antiferroelectric NaNbO 3 causes the induction of ferroelectric properties. It was also found that axial pressure shifts the phase transition and decreases the polarisation. These effects can be mainly connected with change in domain walls dynamics and with the switching of the polarisation under the action of axial pressure.

Polaronic transport in NaNbO3

Abstract Measurements of the temperature dependence of the dc conductivity (α) and the Seebeck coefficient (α) were performed for polycrystalline samples of stoichiometric sodium niobate. The measurements were made in the temperature range from 930 K to 470 K. Obtained results allowed to determine the type and mechanism of electrical conductivity as well as the order of magnitude of charge carriers mobility (μ) and their activation energy.

Phase transitions in LixNa1-xNbO3 solid solution for 0<x<0.1

Abstract Phase transitions in solid solution LixNa1-xO3 have been investigated. Results indicate the strong relation of the parameters of the lower temperature phase transitions on the oxygen vacancies resulting from annealing of the sample at low pressure of oxygen.

DIELECTRIC PROPERTIES OF LEAD-FREE [(1-x)(Na0.5Bi0.5)-xBa]Zr1−y Ti y O3 CERAMICS (x = 0.01, 0.06, 0.085, 0.09, 0.1 AND y = 0.96, 0.97)

ABSTRACT Lead-free ceramics based on (Na0.5Bi0.5TiO3, NBT)-(Ba(Ti, Zr)O3, BTZ) were prepared by solid phase synthesis and hot pressing sintering process and their dielectric properties have been studied. The obtained results were compared with these for pure NBT. The obtained samples show pure perovskite structure. Low frequency (100 Hz-100 kHz) investigations reveal the diffuse phase transitions and relaxorlike behaviour. The obtained results are discussed in terms of inhomogeneity of ions distribution, their ferro- and antiferroactivity and internal stresses. The NBT-BTZ system is expected to be a new promising candidate for lead-free electronic ceramics.

Electrical Transport in Lead-Free [(1−x)(Na0.5Bi0.5)-xBa]Zr1 - yTiyO3 Ceramics (x = 0, 0.06, and y = 0, 0.96)

Lead-free ceramics based on (Na 0.5 Bi 0.5 TiO 3 , NBT)-(Ba(Ti,Zr)O 3 , BTZ) were prepared by solid phase hot pressing sintering process and their ac (σ ac ) and dc (σ dc ) conductivity have been studied (303–753 K). Low frequency (100 Hz–100 kHz) ac conductivity obeys power law σ ac ∼ ω s characteristic for disordered materials. The frequency exponent s is a decreasing function of temperature and tends to zero at high temperatures. Dc conductivity has thermally activated character and possesses four linear parts with four different activation energies and some discontinous changes. However, σ ac (T) possesses two linear parts with two different activation energies and more discontinuous changes than dc conductivity. The results was interpreted by correlated hopping model. The NBT-BTZ system is expected to be a new promising candidate for lead-free electronic ceramics.

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.

Phase transitions in polycrystalline Ba(Ti1−xSnx)O3

Abstract Temperature measurements of dielectric permittivity and pyroelectric current for polycrystalline Ba(Ti1−xSnx)O3-samples have been performed. A decrease of temperature Tm of e;-peak and the increase of diffuseness of the para-ferroelectric phase transition with the increase of x have been observed. The overlap of three phase transitions into one (para-ferroelectric) for x > 0.06 has been confirmed.

Influence of Axial Pressure on Electric Properties of PLuN and 0.6PLuN–0.4PSN Ceramics

The dielectric, pyroelectric and hysteresis loops measurements of PLuN and 0.6PLuN–0.4PSN ceramics, stress-free or under the stress (0–1.5 kbar), have been carried out. It is shown that uniaxial pressure shifts the phase transformation and decreases the thermal hysteresis of the electric permittivity and the field-polarization hysteresis. These changes of properties could be connected with domain wall motion and with switching of the polarization under uniaxial pressure.

Effect of Electromechanical Loading on the Dielectric Properties of PLZT−x/65/35 Ceramics (x = 8 and 8.5)

The influence of uniaxial pressure (0-800 bars) applied parallel to the ac electric field on the dielectric properties of La−modified lead–zirconate−titanate ceramics with the Zr/Ti ratio of 65/35 was investigated. Applying uniaxial pressure leads to the reduction of the peak intensity of the electric permittivity (ϵ), of the frequency dispersion as well as of the dielectric hysteresis. The peak intensity of ϵ becomes diffuse and shifts with increasing the pressure. Our results show that applying uniaxial pressure induces similar effects as increasing the Ti−ion concentration in PZT system. We interpreted our results based on domain switching processes under the action of combined electromechanical loading. These studies clearly showed that the applied stress has a significant influence on the dielectric properties of perovskite ceramics.

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.