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Lead-free Ba1−xSrxTiO3 (BST) (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.45) ceramics were successfully prepared via the solid-state reaction route. A pure perovskite crystalline structure was identified for all compositions by X-ray diffraction analysis. The basic phase transition temperatures in these ceramics were studied over a wide temperature range. A change in symmetry from a tetragonal to cubic phase was detected, which was further proven by phonon anomalies in composition/temperature-dependent Raman spectra. The incorporation of Sr2+ into BaTiO3 (BT) lead to a shift in the phase transitions to lower temperatures, suppressing the ferroelectric properties and inducing relaxor-like behavior. Therefore, it was reasonable to suppose that the materials progressively lack long-range ordering. The initial second-harmonic generation (SHG) measurements demonstrated that the cubic phase of BST ceramics is not purely centrosymmetric over a wide temperature interval. We discussed the possible origin of the observed effects, and showed that electric field poling seems to reconstruct the structural ordering destroyed by the introduction of Sr2+ to BT. In the first approximation, substitution of Sr for larger Ba simply reduced the space for the off-central shift in Ti in the lattice and hence the domain polarization. A-site cation ordering in BST and its influence on the density of electronic states were also explored. The effect of doping with strontium ions in the BST compound on the density of electronic states was investigated using ab initio methods. As the calculations showed, doping BT with Sr2+ atoms led to an increase in the bandgap. The proposed calculations will also be used in the subsequent search for materials optimal for applications in photovoltaics. [ABSTRACT FROM AUTHOR]

Na0.5Bi0.5TiO3 (NBT) and Fe- and Mn-modified NBT (0.5 and 1 mol%) ceramics were synthesized by the solid-state reaction method. The crystal structure, dielectric and thermal properties of these ceramics were measured in both unpoled and poled states. Neither the addition of iron/manganese to NBT nor poling changed the average crystal structure of the material; however, changes were observed in the short-range scale. The changes in shapes of the Bragg peaks and in their 2Θ-position and changes in the Raman spectra indicated a temperature-driven structural evolution similar to that in pure NBT. It was found that both substitutions led to a decrease in the depolarization temperature Td and an increase in the piezoelectric coefficient d33. In addition, applying an electric field reactivated and extended the ferroelectric state to higher temperatures (Td increased). These effects could be the result of: crystal structure disturbance; changes in the density of defects; the appearance of (FeTiˈ-), (Mn′Ti-V••O) and (Mn″Tii-V••O)—microdipoles; improved domain reorientation conditions and instability of the local polarization state due to the introduction of Fe and Mn into the NBT; reinforced polarization/domain ordering; and partial transformation of the rhombohedral regions into tetragonal ones by the electric field, which supports a long-range ferroelectric state. The possible occupancy of A- and/or B-sites by Fe and Mn ions is discussed based on ionic radius/valence/electronegativity principles. The doping of Fe/Mn and E-poling offers an effective way to modify the properties of NBT. [ABSTRACT FROM AUTHOR]

Ferroelectric ceramics BaTiO3:x%Eu (x = 0, 0.1, 1, 2, 3) were synthesized by a conventional method. Structural investigation confirmed that all ceramics possessed tetragonal (P4mm) symmetries at room temperature for the undoped ceramics as well as for the doped ceramics. Furthermore, a slight downshifting of the Curie temperature (TC) with an increasing Eu3+ doping amount has been noted. The Raman spectra unveiled the existence of new modes for higher-doped BaTiO3:x%Eu (BTEx) which are related to local disorders and defects. The ferroelectric properties were found to depend on both doping and the microstructure. The electrocaloric effect was also studied for those ceramics. It was observed that ΔT decreases with doping; however, the temperature range of its occurrence widens considerably. [ABSTRACT FROM AUTHOR]

The electrocaloric effect (ECE) was investigated in BaTiO3 ceramics, pure and doped with 2% of Eu3+ ions. The temperature and electric field dependences of ECE were investigated by the indirect method. Based on Maxwell relations, the ECE was characterized via P–T curves under different electric fields. The ECE experiments have been carried out from room temperature through the phase transition region and in the paraelectric phase. A normal positive ECE was found around the phase transition point and is of the order of 0.6 K for pure BaTiO3 and 0.15 K for the BT doped with Eu ions. The abnormal negative ECE was detected for the BaTiO3 ceramic doped with Eu ions above the temperature of the phase transition. This phenomenon was related to the existence of defects that originates from the fixed local polarization of defect dipoles. [ABSTRACT FROM AUTHOR]

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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. [ABSTRACT FROM PUBLISHER]

0.82K0.5Bi0.5TiO3-0.18PbTiO3ceramic 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. [ABSTRACT FROM AUTHOR]

Lead-free Na0.5K0.5NbO3and Na0.5K0.5NbO3+0.5mol%MnO2ceramics were fabricated by solid state hot pressing sintering process. The phase structure and thermal, dielectric and ferroelectric properties of these ceramics were investigated. X-ray measurements showed that all samples have a single perovskite structure and possess orthorhombic–tetragonal and tetragonal–cubic phase transitions. Sequence of phase transitions was confirmed by differential scanning calorimetry (DSC) and dielectric measurements. Obtained results showed that optimal temperature sintering of Na0.5K0.5NbO3+0.5mol%MnO2ceramics is 1100 °C. The results show that investigated ceramics are one of the promising materials as electronic ceramics. [ABSTRACT FROM AUTHOR]

The BaZrxTi1-xO3 for 0⩽x⩽15 ceramics were prepared by a conventional solid state reaction method and were determined by an X-ray diffraction (XRD) and scanning electron microscopy (SEM) for crystallographic, surface morphological and compositional studies. A single phase with perovskite structure was identified in the samples at room temperature. No significant impurities were detected in an EDS spectrum and the samples are in good stoichiometric ratio. The temperature dependence of electric conductivity was evaluated in the temperature range from 300 to 550 K for a selected frequency by a HP4284 LCR meter. The activation energy was calculated from the Arrhenius plots. [ABSTRACT FROM PUBLISHER]