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The mechanical properties of Mn- and Fe-doped Na0.5Bi0.5TiO3 ceramics in unpoled and poled states were examined and analyzed for the first time through measurements of Young's modulus, the elastic modulus, Poisson's number, compressibility modulus K, hardness, fracture toughness and bending strength on one hand and by stress–strain measurements on the other hand. It was found that both the introduction of Fe and Mn ions into Na0.5Bi0.5TiO3 and E-poling lead to improvements in their mechanical properties. The additives also cause improvement of the piezoelectric properties. The stress–strain curves revealed a changing mechanical response with the Mn and Fe doping of the NBT. With the doping, there was a decrease in coercive stress, which enhanced the remnant strain. In contrast, the E-poling led to an increase in the coercive stress, which reduced the remnant strain. Induced internal stresses associated with non-180° domain switching were determined. It was found that the investigated materials displayed significant ferroelastic deformation and large remnant polarization even under external stress of 180–250 MPa. Modification of NBT by Mn and Fe ions and E-poling were found to be effective ways of improving actuator performance and controlling operating stresses in order to minimize irreversible fatigue damage. The results suggest that the investigated materials could replace PZT ceramics in actuator applications where high blocking stress is required. [ABSTRACT FROM AUTHOR]

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]

The single crystals of lead-free Na 0.5 Bi 0.5 TiO 3 were grown using the Czochralski method. The energy gaps determined from X-ray photoelectron spectroscopy (XPS) and optical measurements were approximately 2.92 eV. The current-voltage characteristics, depolarization current, dc (σ dc ) and ac (σ ac ) electrical conductivity, and Seebeck coefficient of the crystals were investigated. The frequency/temperature-dependent electrical properties were also measured and analyzed through complex impedance spectroscopy. An overlapping reversible insulator-metal transition (resistive switching) on nanoscales, caused by the electric field, was detected. Most of these properties were measured for the first time. The activation energy values determined from the conductivity data, the imaginary part of the electric impedance and the modulus indicate that the relaxation process in the high-temperature range is attributable to both single and double ionized oxygen vacancies, in combination with the hopping of electrons between Ti 4+ and Ti 3+ . P-type electrical conductivity was also found. These discoveries create new possibilities of reducing the electrical conductivity of NBT and improving the process of effectively poling this material. Our results indicate the possibility of tuning the material properties by intentionally creating non-stoichiometry/structural defects (oxygen vacancies, cation excess and cation deficiency)., Competing Interests: Declarations. Competing interests: The authors declare no competing interests., (© 2025. The Author(s).)