Porous piezoceramics are attractive for high-sensitivity sensing and energy conversion due to their low density, reduced dielectric constant (ε_r), and good mechanical compliance. However, increasing porosity is often accompanied by a significant reduction in the piezoelectric charge coefficient (d₃₃), creating an intrinsic trade-off that limits the practical use of porous structures in high-sensitivity piezoelectric devices and leaves their overall performance advantages under debate. In this work, we overcome this challenge by developing a fully open-cell, three-dimensionally interconnected Pb(Zr_1/2Ti_1/2)O₃–Pb(Zn_1/3Nb_2/3)O₃–Pb(Ni_1/3Nb_2/3)O₃ (PZT–PZN–PNN, PZNNT) porous piezoceramic (3D-PPC). Despite an ultrahigh porosity of 92%, the material maintains a high d₃₃ of approximately 470 pC/N, approximately 90% of that of the dense ceramic. The effective ε_r is reduced to approximately 140 (a 94% decrease), leading to an approximately 14-fold enhancement in the piezoelectric voltage coefficient g₃₃ (approximately 380×10⁻³ Vm/N). Combined microstructural characterization, domain analysis, defect studies, and multiphysics simulations show that the exceptional performance arises from synergistic effects of heterogeneous stress and electric fields, multiscale domain structures, and defect-mediated regulation within the three-dimensionally interconnected porous architecture. Finally, the material generates peak output voltages up to 200 V under subtle mechanical excitation and achieves an ultrahigh sensitivity of 38.7 V/kPa. These results show that three-dimensionally interconnected porous architectures are not merely passive means of reducing dielectric permittivity but also active structural strategies for tuning local fields and polarization behavior.

Piezocomposites with both flexibility and electromechanical conversion characteristics have been widely applied in various fields, including sensors, energy harvesting, catalysis, and biomedical treatment. In the composition of piezocomposites or their preparation process, a category of materials is commonly employed that do not possess piezoelectric properties themselves but play a crucial role in performance enhancement. In this review, the concept of auxiliary phase is first proposed to define these materials, aiming to provide a new perspective for designing high-performance piezocomposites. Three different categories of modulation forms of auxiliary phase in piezocomposites are systematically summarized, including the modification of piezo-matrix, the modification of piezo-fillers, and the construction of special structures. Each category emphasizes the role of the auxiliary phase and systematically discusses the latest advancements and the physical mechanisms of the auxiliary phase enhanced flexible piezocomposites. Finally, a summary and future outlook of piezocomposites based on the auxiliary phase are provided.

Piezoelectric energy harvesters (PEHs) have attracted significant attention with the ability of converting mechanical energy into electrical energy and power the self-powered microelectronic components. Generally, material's superior energy harvesting performance is closely related to its high transduction coefficient (d₃₃×g₃₃), which is dependent on higher piezoelectric coefficient d₃₃ and lower dielectric constant ε_r of materials. However, the high d₃₃ and low ε_r are difficult to be simultaneously achieved in piezoelectric ceramics. Herein, lead zirconate titanate (PZT) based piezoelectric composites with vertically aligned microchannel structure are constructed by phase-inversion method. The polyvinylidene fluoride (PVDF) and carbon nanotubes (CNTs) are mixed as fillers to fabricate PZT/PVDF&CNTs composites. The unique structure and uniformly distributed CNTs network enhance the polarization and thus improve the d₃₃. The PVDF filler effectively reduce the ε_r. As a consequence, the excellent piezoelectric coefficient (d₃₃ = 595 pC/N) and relatively low dielectric constant (ε_r = 1,603) were obtained in PZT/PVDF&CNTs composites, which generated an ultra-high d₃₃×g₃₃ of 24,942 × 10⁻¹⁵ m²/N. Therefore, the PZT/PVDF&CNTs piezoelectric composites achieve excellent energy harvesting performance (output voltage: 66 V, short current: 39.22 μA, and power density: 1.25 μW/mm²). Our strategy effectively boosts the performance of piezoelectric-polymer composites, which has certain guiding significance for design of energy harvesters.

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 $g_{33}=d_{33}/({\epsilon }_0{\epsilon }_{\text{r}})$ and $d_{33}=2Q{\epsilon }_0{\epsilon }_{\text{r}}{P}_{\text{r}}$. 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.