Na _1/2 Bi _1/2 TiO ₃ ‐based materials have been earmarked for one of the first large‐volume applications of lead‐free piezoceramics in high‐power ultrasonics. Zn ²⁺ ‐doping is demonstrated as a viable route to enhance the thermal depolarization temperature and electromechanically harden (1‐ y )Na _1/2 Bi _1/2 TiO ₃ ‐ y BaTiO ₃ (NBT100 y BT) with a maximum achievable operating temperature of 150 °C and mechanical quality factor of 627 for 1 mole % Zn ²⁺ ‐doped NBT6BT. Although quenching from sintering temperatures has been recently touted to enhance T _F‐R , with quenching the doped compositions featuring an additional increase in T _F‐R by 17 °C, it exhibits negligible effect on the electromechanical properties. The effect is rationalized considering the missing influence on conductivity and therefore, negligible changes in the defect chemistry upon quenching. High‐resolution diffraction indicates that Zn ²⁺ ‐doped samples favor the tetragonal phase with enhanced lattice distortion, further corroborated by ²³ Na Nuclear Magnetic Resonance investigations.

Na_0.5Bi_0.5TiO₃-based materials have been widely investigated over the past two decades due to their giant strain and stable mechanical quality factor, which render them potential alternatives to lead-based materials. One of the limiting factors of these materials has been the relatively lower depolarization temperatures, which restrict their use in high power ultrasonics. This work explores the phase evolution and electromechanical properties of (1 − x)Na_0.5Bi_0.5TiO₃–xBiFeO₃ (x = 0–0.60, labelled as NBT–100xBFO) and demonstrates a composition-induced relaxor-to-ferroelectric crossover. With increasing BFO content, the samples exhibit R3c symmetry and the unit cell volume increases monotonously. The electromechanical properties indicate a criticality at x = 0.30, beyond which, NBT–100xBFO becomes ferroelectric. The unit cell distortions reflect the changes observed in the electrical response. These results are further corroborated by the temperature dependent strain-field hysteresis and lamellar domain structure in the TEM images of unpoled NBT–50BFO, indicating a stable, long-range ferroelectric order. The outcome of this study indicates that NBT–100xBFO could be a potential high temperature ferroelectric, which can be further tailored to surpass the existing temperature limits of the NBT class of materials.

Perovskite oxides with mixed ionic and electronic conductivities are very promising candidates for their application as energy materials related to fuel cell and metal air battery integration. In this article, we report on the systematic characterization of mixed proton and electron conducting compounds of composition BaFe_1−xCo_xO_3−y−δ(OH)_y synthesized via nebulized spray pyrolysis. Independent of the value of x, all samples BaFe_1−xCo_xO_3−y−δ(OH)_y were found to crystallize in an orthorhombic ordering/distortion variant of the perovskite type structure (space group Cmcm) and are isotypic to the border phases (x = 0 or 1) reported previously. A minimum water content was observed for the composition with x = 0.5, which increases steadily for Co or Fe richer compositions. Impedance studies show that the conductivity increases with increasing Co-content, with BaCo_0.5Fe_0.5O_2.07(OH)_0.74 showing a total electrical conductivity of 10⁻⁷ S cm⁻¹ at 298 K, an order of magnitude higher than found for BaFeO_2.33(OH)_0.33. Further, bifunctional catalytic activity for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) was found for the compounds of the series as investigated in 0.1 M KOH, with BaFe_0.8Co_0.2O_3−y−δ(OH)_y possessing the best bifunctional performance parameter of ΔU = 1.10 V, which is comparable to that of other non-precious metal catalysts.