Lead-free Ba_1−xSr_xTiO₃ (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.

The low-lead (1-x)Pb(Mg_1/3Nb_2/3)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(Mg_1/3Nb_2/3)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(Mg_1/3Nb_2/3)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.

The preparation of high-density lead-free potassium-bismuth titanate K_0.5Bi_0.5TiO₃ about 96–98% of the calculated density (X-ray), confirmed by the Archimedes method, is presented. All stages of the technological process are explained in detail. The control of microstructure was performed by scanning electron microscopy. The crystal structure and phase content of samples were determined by X-ray diffraction at each stage of sintering. Four types of samples were obtained under various technological conditions. The ultrasonic measurements of the obtained samples were carried out and basic parameters were determined, such as Young and Kirchoff modulus and Poisson’s ratio were determined at room temperature. The dielectric measurements show that the maximum value of dielectric permittivity is shifted towards higher temperatures as the frequency increases. This feature is characteristic of ferroelectric relaxor materials. The presented materials can be a good starting point for the development of lead-free ceramics.