Bi₇Ti_4.5-xMn_xW_0.5O₂₁ (BTW-BIT-x Mn) bismuth layered-structure ceramics were synthesized by using the traditional solid-state method. Structure and electrical properties of the Bi₇Ti_4.5-xMn_xW_0.5O₂₁were systematically studied. XRD and SEM results showed that all the samples were single phase bismuth layered compound and the grain growth was inhibited due to the doping with Mn. Electrical properties of the ceramics were improved after doping with Mn and the Bi₇Ti_4.45Mn_0.05W_0.05O₂₁ sample exhibited optimal properties, with a piezoelectric constant d₃₃ of 19.3 pC/N, Curie temperature of 701 ℃ and DC resistivity of 2.1×10⁸ Ω cm at 500 ℃. The annealing data indicated that more than 80% of the initial value of piezoelectric constant was retained at 550 ℃, demonstrating that the material has high thermal stability. Such BTW-BIT-x Mn ceramics have great potential for high-temperature piezoelectric applications.

BaBi₈Ti_7−xMg_xO_27−δ (x=0, 0.2, 0.4, 0.6, 0.8) intergrowth bismuth layered lead-free piezoelectric ceramics were prepared by using the conventional solid-state reaction method. The effect of Mg²⁺ on structure, electrical properties and temperature stability of the ceramics was studied. All the samples have a single phase structure. With increasing content of Mg²⁺, both the dielectric constant and dielectric loss showed a decreasing trend, while the impedance and activation energy increase at high temperatures. In addition, a small quantity of Mg²⁺ resulted in a variation in the microstructure from plate-like grains to particle-like grains, leading to an improvement in piezoelectric properties of the ceramics. The sample with x=0.60 exhibited optimum electrical properties, with Curie temperature of about 480 ℃ and piezoelectric constant (d₃₃) of 18.8 pC·N⁻¹, which is higher than that of the undoped sample by about 250%.

Bi_0.47Na_0.47Ba_0.06Cu_0.015Ti_0.985O₃ (BNBCT) lead-free piezoelectric ceramics were prepared by using the solid-state reaction technique. Samples were sintered at 1090 ℃ for 2 h in oxygen (BNBCT-O₂), air (BNBCT-Air), and nitrogen (BNBCT-N₂). Effects of sintering atmospheres on structure and electrical properties of the BNBCT ceramics were thoroughly studied. X-ray diffraction (XRD) results revealed that all samples exhibited pure perovskite phase. XRD Rietveld refinements confirmed that the BNBCT-O₂ ceramics have strong lattice distortion. According to complex impedance spectra, the electrical response activation energy, activation energy of conductivity, and O1s X-ray photoelectron spectra (XPS), it is indicated that oxygen vacancy concentrations are different in different sintering atmosphere. When the oxygen content in sintering atmospheres is sufficiently high, oxygen vacancies can be easily inhibited. Compared with BNBCT-Air and BNBCT-N₂, the BNBCT-O₂ exhibited the highest piezoelectric coefficient (d₃₃=227 pC·N^-1) and the largest remnant polarization (P_r=31.9 μC·cm^-2). It is therefore concluded that the microstructure and electrical properties of BNBCT were related to oxygen vacancy concentration, which could be controlled by the sintering atmosphere. This work provides a feasible way to improve the piezoelectric properties of Bi_0.47Na_0.47Ba_0.06TiO₃-based ceramics by simply controlling the sintering atmosphere.

(1–x)BiFeO₃–xBaTiO₃(BF–xBT, x=0.28,0.29,0.30,0.31) piezoelectric ceramics were prepared by a conventional sintering technology. The relationship between the phase structure and dielectric, ferroelectric and piezoelectric properties of the ceramics near the phase boundary was investigated. Based on the results by X-ray diffraction, all the samples present a pure perovskite phase structure without any impurity phase, and all the ceramics are located around the rhombohedral–pseudocubic phase boundary. The phase structure gradually transforms from rhombohedral to pseudocubic phase as x increases, and the content of R and pC phase tends to be equal when x=0.30, showing the optimum electrical properties (i.e., piezoelectric coefficient (d₃₃) =165 pC/N, remanent polarization (P_r) = 26.80 μC/cm₂, and the Curie temperature (T_C) = 465 ℃). In addition, the changes of Raman vibration mode and diffuseness factor of the samples after quenching indicate that the quenching process can effectively improve the long range order degree and the temperature stability of ferroelectric phase of the samples, resulting in a further increase in the Curie temperature of BF–xBT ceramics. For a ceramic BF–0.30BT, the enhanced dielectric and ferroelectric properties are obtained due to its more proper R/pC phase ratio and quenching process. Also, the relationship between the phase structure evolution and piezoelectric properties of BF–xBT ceramics was revealed, and the electrical properties of BF–xBT ceramics were further optimized by quenching process, so as to provide a reference for broadening the application temperature range of the BF–BT system materials.