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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]

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]

The differences between the physical properties of BaTiO3and BaTiO3+0.1wt.% Eu2O3were identified. Scanning electron microscopy studies show that the small addition of europium to barium titanate ceramics results in a decrease in the average grain size from 5–10 μm to 2–4 μm. The alternating current measurements were performed in the temperature range from 150 to 600 K and in the frequency range from 0.1 Hz to 10 MHz. Both thermal analysis and dielectric spectroscopy indicate that the temperature of the ferroelectric–paraelectric phase transition shifts towards room temperature. [ABSTRACT FROM AUTHOR]