Bartosz Handke

Influence of Sr-Substitution on Diffuseness of (Ba1-xSrx)TiO3 Phase Transitions

The results of X-ray diffraction (XRD), scanning electron microscopy (SEM) and dielectric measurements performed for samples of the polycrystalline solid solutions of (Ba1-xSrx)TiO3, are presented. An increase of diffuseness of ferroelectric phase transition and a decrease of the temperature Tm (the temperature of the maximum value of the real part of the electric permittivity; ϵ′) with increase of Sr concentration is observed. Values of the phase angle (approximate to −90°) measured in broad range of temperatures suggest the occurrence of polar regions (clusters) in the temperature range of paraelectric (PE)-ferroelectric (FE) phase transition.

Raman spectra and anomalies of dielectric properties and thermal expansion of lead-free (1−x)Na0.5Bi0.5TiO3-xSrTiO3 (x = 0, 0.08 and 0.1) ceramics

ABSTRACT Thermal expansion, Raman and dielectric properties of the lead-free (1−x)Na0.5Bi0.5TiO3-xSrTiO3 (x = 0, 0.08 and 0.1) ceramic solid solutions, fabricated by the conventional solid-state reaction method, were investigated. The Sr-doping results in an increase of the dielectric permittivity, broadening of the permittivity maximum, enhancement of the relaxation near depolarization temperature, broadening of the Raman bands and shift of all anomalies toward lower temperatures. The observed effects are attributed to an increase of the degree of cationic disorder and enhancement of the relaxor-like features. Anomalies in the thermal expansion strain were observed at the temperatures corresponding to the dielectric anomalies but not related to any phase transitions. These anomalies are supposed to follow changes of the averaged unit cell volume in the temperature interval of tetragonal and rhombohedral phase coexistence.

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.

Thermal, Raman, dielectric and ferroelectric properties of 0.975BaTiO3-0.025Pb(Zn1/3Nb2/3)O3 ceramic

ABSTRACT A new low-lead content 0.975BaTiO3-0.025PbZn1/3Nb2/3O3 (0.975BT-0.025PZN) ceramic with a high relative density and good mechanical quality was fabricated by the SPS method. X-ray diffraction measurements showed that the obtained specimen possesses a pure perovskite structure. The composition undergoes a sequence of phase transitions as pure BT. Dielectric studies revealed that the dielectric permittivity decreases at its maximum and the phase transitions shift after PZN-doping of BT. In addition, the dielectric dispersion and polarization increases and decreases, respectively. Possible reasons for the observed properties change are discussed. The results show that the investigated ceramic is a promising low-lead material for electronic applications.

Influence of Sr addition on structural, dielectric and Raman properties of Na0.5Bi0.5TiO3 ceramics

ABSTRACT Lead free (Na0.5Bi0.5)1-xSrxTiO3 (x = 0, 0.01 and 0.02) ceramics were produced by a conventional solid-state sintering method. X-ray diffraction analysis shows that the obtained samples possess the perovskite structure with rhombohedral symmetry. The microstructure study shows a dense structure, in agreement with the relative density (above 97%). Dielectric analysis revealed the diffuse character of the electric permittivity anomalies and their shift to a lower temperature range after Sr doping of NBT. The Raman spectra are similar for all samples in agreement with the X-ray diffraction data. The possible origin of the observed effects was discussed.

Thermal, dielectric and ferroelectric properties of 0.925BaTiO3–0.075Pb(Zn1/3Nb2/3)O3 ceramic

New low-lead content 0.925BaTiO3–0.075PbZn1/3Nb2/3O3 (0.925BT–0.075PZN) ceramic was fabricated by the spark-plasma-sintering method. X-ray diffraction measurements showed that the obtained specimen possesses a pure perovskite structure. The microstructure investigation indicated a dense ceramic structure with 95% relative density determined by the Archimedes method. Composition undergoes a sequence of phase transitions as pure barium titanate (BT). Dielectric study revealed that the electric permittivity decreases at its maximum and the phase transition shifts to a higher temperature after lead zinc niobate doping of BT. Besides, the dielectric dispersion and polarization increases and decreases, respectively. Obtained results were discussed in term of the difference between ionic size and its mass and local elastic and electric fields. The results show that investigated ceramic is one of the promising low-lead materials for electronic applications.

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.