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In this work, Nb‐doped 0.75SrTiO3‐0.25BiFeO3 (ST‐BF) lead‐free ceramics are designed and synthesized using a conventional solid‐state reaction method. The influence of Nb doping on the microstructure, dielectric, and electrical properties are systematically investigated. With the increase of Nb concentration, the crystal structure of ST‐BF remains pseudo‐cubic as exhibited in the X‐ray diffraction patterns. The grain size is found to increase from 0.33 to 6.23 μm, and then decrease to 1.88 μm by Nb doping, along with a clear heterogeneous core–shell microstructure. A relatively low dielectric loss (∼0.1, at 1 kHz) and a stable dielectric constant (∼700, at 1 kHz) are obtained for the 0.03 Nb‐doped ST‐BF composition at room temperature. Impedance spectroscopy analysis shows that Nb doping in ST‐BF increases the total resistivity, forming an electrically conductive core and a nonconductive shell, with enhanced activation energy. The results may provide a feasible approach to develop novel ST‐based lead‐free dielectric ceramics for capacitor applications. [ABSTRACT FROM AUTHOR]

Abstract: For the first time, potassium sodium niobate (KNN)‐based lead‐free piezoelectric ceramic coating with strong piezoelectric response was fabricated on stainless steel substrates by thermal spray process, after introducing NiCrAlY and yttria‐stabilized zirconia (YSZ) intermediate layers. A large effective piezoelectric coefficient (d33) of 125 pm/V was obtained with the thermal‐sprayed KNN‐based ceramic coating on the steel substrates. The mechanisms of improving the structure and enhancing the properties of the KNN‐based piezoelectric ceramic coatings by introducing the intermediate layers were analyzed. Ultrasonic transducers were designed and fabricated from the KNN‐based coatings directly formed on a steel plate structure, and the feasibility for generation and detection of ultrasonic waves for structural health monitoring using the thermal‐sprayed lead‐free piezoelectric ceramic coating was demonstrated. [ABSTRACT FROM AUTHOR]

• Significantly reduced conductivity in ST-based ceramics was achieved by excess Bi. • Heterogeneous core–shell microstructure was revealed by SEM and Impedance. • Excellent die/ferroelectric properties were obtained, attractive for capacitors. Lead-free dielectric ceramics 0.75SrTiO 3 -0.25BiFeO 3 (ST-BF) with an extra amount of bismuth (Bi) are synthesized by the conventional solid-state reaction method. The crystal structures of ST-BF retain pseudo-cubic phase as Bi content increases. The grain size is found to significantly increase from 1.8 to 4.9 µm and then fall to 3.3 µm in the presence of excess Bi, exhibiting a distinct heterogeneous core–shell microstructure. Impedance spectroscopy data indicates that with increasing excess Bi content to 2 mol%, the shell resistivity increases significantly to ∼ 9 MΩ cm with the largest volume fraction of the shell/core area, and both the core and shell activation energies are increased, resulting in reduced dielectric loss of ∼ 0.08 at 1 kHz and high breakdown strength of ∼ 140 kV cm−1. This work provides a potential strategy for further improvement of ST-BF for capacitor applications. [ABSTRACT FROM AUTHOR]