Piezoelectric nanogenerators with the ability to convert mechanical energy into electrical energy for energy harvesting have prompted widespread concern. In this work, gradient porous PZT ceramics with a cellular region, transition region, progressive lamellar region and homogeneous lamellar region were prepared via freeze casting method. PDMS as a flexible matrix was introduced into the pore space of porous PZT ceramics to form piezoelectric composites. The gradient porous structure promoted the ability of stress transfer, and greatly improved the efficiency of electromechanical conversion. Among these regions, the PENG in the progressive lamellar region displayed the maximum optional electric output performance. The PENG generated the maximum output voltage of 152 V and current of 17.5 μA, which were 2 times and 1.6 times higher than those of piezoelectric composites with randomly dispersed PZT ceramic particles under the given external mechanical stress. The sensitivity of PENG based on the gradient porous PZT ceramics was 1.52 V N⁻¹, which possessed a remarkable superiority in comparison with other PENG with 3D interconnected structure. Moreover, the instantaneous power reached 1.1 mW, which could light up 96 LEDs. This work demonstrated the potential application of porous piezoelectric composites in energy harvesting.

The synergistic contributions of high P_max, small P_r and large E_b endow the BiFeO₃-based ceramics with relaxor ferroelectric characteristics, due to which an ultrahigh W_rec of 13.9 J cm⁻³ and high η of 89.6% have been achieved synchronously.

The intrinsic conduction mechanism and optimal sintering atmosphere of (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ (BCZT) ceramics were regulated by Mn-doping element in this work. By Hall and impedance analysis, the undoped BCZT ceramics exhibit a typical n-type conduction mechanism, and the electron concentration decreases with the increasing oxygen partial pressure. Therefore, the undoped ceramics exhibit best electrical properties (piezoelectrical constant d₃₃ = 585 pC·N⁻¹, electro-mechanical coupling factor k_p = 56%) in O₂. A handful of Mn-doping element would transfer the conduction mechanism from n-type into p-type. And the hole concentration reduces with the decreasing oxygen partial pressure for Mn-doped BCZT ceramics. Therefore, the Mn-doped ceramics sintered in N2 have the highest insulation resistance and best piezoelectric properties (d₃₃ = 505 pC·N⁻¹, k_p = 50%). The experimental results demonstrate that the Mn-doping element can effectively adjust the intrinsic conduction mechanism and then predict the optimal atmosphere.

Piezoelectric energy harvesters (PEHs) fabricated using piezoceramics could convert directly the mechanical vibration energy in the environment into electrical energy. The high piezoelectric charge coefficient (d₃₃) and large piezoelectric voltage coefficient (g₃₃) are key factors for the high-performance PEHs. However, high d₃₃ and large g₃₃ are difficult to simultaneously achieve with respect to g₃₃ = d₃₃/(ε₀ε_r) and d₃₃ = 2Qε₀ε_rP_r. Herein, the energy harvesting performance is optimized by tailoring the CaZrO₃ content in (0.964−x)(K_0.52Na_0.48)(Nb_0.96Sb_0.04)O₃ −0.036(Bi_0.5Na_0.5)ZrO₃−xCaZrO₃ ceramics. First, the doping CaZrO₃ could enhance the dielectric relaxation due to the compositional fluctuation and structural disordering, and thus reduce the domain size to ∼30 nm for x = 0.006 sample. The nanodomains switch easily to external electric field, resulting in large polarization. Second, the rhombohedral–orthorhombic–tetragonal phases coexist in x = 0.006 sample, which reduces the polarization anisotropy and thus improves the piezoelectric properties. The multiphase coexistence structures and miniaturized domains contribute to the excellent piezoelectric properties of d₃₃ (354 pC/N). Furthermore, the dielectric relative permittivity (ε_r) reduces monotonously as the CaZrO₃ content increases due to the relatively low ion polarizability of Ca²⁺ and Zr⁴⁺. As a result, the optimized energy conversion coefficient (d₃₃ × g₃₃, 5508 × 10⁻¹⁵ m²/N) is achieved for x = 0.006 sample. Most importantly, the assembled PEH with the optimal specimen shows the excellent output power (∼48 µW) and lights up 45 red commercial light-emitting diodes (LEDs). This work demonstrates that tailoring ferroelectric/relaxor behavior in (K,Na)NbO₃-based piezoelectric ceramics could effectively enhance the electrical output of PEHs.