Enhancing the piezoelectricity of CaBi₄Ti₄O₁₅ (CBT) ceramics is crucial for improving their application potential in high-temperature piezoelectric devices. Here, we propose a strategy involving the introduction of larger Na/Bi ions at the A-site, effectively inhibiting the tilt of oxygen octahedra and flattening the potential energy profile. This flattening enhances the variation in polarization under external fields. Concurrently, substituting Nb/Mn at the B-site increases the deviation between positive and negative ionic centers, leading to stronger spontaneous polarization, while the induced defect dipoles restrict oxygen vacancy migration and increase the direct current resistivity (ρ_dc). The flattened potential energy profile and increased spontaneous polarization significantly enhance the overall performance of CBT ceramics, with the piezoelectric constant (d₃₃) reaching 25 pC/N when the Curie temperature (T_C) = 752 °C. Piezoresponse force microscopy (PFM) and transmission electron microscopy (TEM) revealed submicron-long rectangular domains and nanoscale domains in the modified composition, indicating a high density of domain walls. This study presents an effective approach for enhancing the piezoelectric properties of bismuth layered-structured ferroelectrics (BLSFs), thereby improving the application potential of BLSFs at high temperatures.

In this work, different amount of Cr₂O₃ (x = 0–0.3 wt%) as dopant were doped into the Aurivillius-type compound Bi_2.8Gd_0.2TiNbO₉ (BGTN), such a kind of Gd/Cr co-doped Bi₃TiNbO₉ ceramics with improved electrical properties were synthesized by the convenient solid-state reaction route. The substitution of Cr³⁺ for Ti⁴⁺ at B-site induced the lattice distortion of pseduo-perovskite layer. Fewer Cr₂O₃ dopant (x < 0.2) resulted in the grain refinement of ceramics. After Cr₂O₃ was added into BGTN, T_C decreased to the vicinity of 908 ℃. Below T_C, the relaxed dielectric response resulted from charge carriers hopping induced another board dielectric permittivity peak, whose starting temperature shifts toward lower side gradually with increase of x. The values of E_a^con calculated from the Arrhenius relationship between conductivity and temperature indicated the intrinsic conduction at high temperature is dominated by the long-range migration of doubly ionized oxygen vacancies. Moderate Cr₂O₃ dopant (x = 0.1–0.25) are conducive to the enhancement of piezoelectric property and thermal stability. The sample with x = 0.2 achieved both a high T_C~903 ℃ and a high d₃₃~18 pC/N at the same time. Also, its d₃₃ can retain 80% of the initial value after the sample was annealed at 800 ℃ for 4 h.

In this paper, both the 1D radial mode and the equivalent circuit of a piezoceramic disk resonator were theoretically analyzed based on IEEE standards. And then, the radial resonance frequency spectra of the PZT-based (Nb/Ce co-doped Pb(Zr_0.52Ti_0.48)O₃, abbreviated as PZT-NC) piezoceramic circular disks were measured by an impedance analyzer. A set of resonance frequency spectra including six electrical parameters: Z, R, X, Y, G, and B, were used for making a value distinction between three possible resonance frequencies, and between three possible antiresonance frequencies. A new-form Nyquist diagram was depicted to describe the position relations of these characteristic frequencies. Such a complete resonance frequency spectrum was used to perform the accurate calculation of some material constants and electromechanical coupling parameters for the PZT-NC piezoceramics. Further, the frequency dependence of the AC conductive behavior of the specimen was characterized by the complex impedance measurement. The values of AC conductivity at resonance/antiresonance were deduced from the equivalent circuit parameters. Moreover, the Van Dyke circuit model was assigned to each element contribution and the simulated curves showed a nice fitting with the experimental results. Finally, an additional impedance analysis associated with resonance frequency calculation revealed a complicated coupled vibration mode existing in the annular disk specimen.

In this work, we present a new piezoelectric solid solution consisting of two typical alkali niobate-based materials, K_0.5Na_0.5NbO₃ (KNN) and Li_0.15Na_0.85NbO₃ (LNN). Although KNN and LNN have the same perovskite structure, they exhibit extremely different electrical properties and mechanical behaviors. The phase structures, electrical and mechanical evolutions of the new lead-free piezoelectric materials with different ratios of KNN and LNN are comprehensively and theoretically investigated. According to the X-ray diffraction patterns and curves of permittivity versus temperature, a series of complicated phase transitions can be found with varied LNN content. Rietveld refinement results based on XRD patterns reveal an oxygen octahedron tilting in the LNN-rich crystal structure, and simultaneously the reasons for octahedron tilting are discussed. The distorted crystal structure is accompanied by extremely decreased electric properties but increased mechanical properties, which reveals electrical and mechanical properties of alkali niobate-based piezoelectric ceramics strongly depend on their inner structures, and the enhancement of intrinsic hardness results in the deterioration of piezoelectric properties. Our work exhibits the detailed evolutions of structure, electrical and mechanical properties from KNN to LNN, which provides experimental and theoretical basis for development of new alkali niobate-based piezoelectric materials.