How to achieve synergistic improvement of permittivity (ε_r) and breakdown strength (E_b) is a huge challenge for polymer dielectrics. Here, for the first time, the π-conjugated comonomer (MHT) can simultaneously promote the ε_r and E_b of linear poly(methyl methacrylate) (PMMA) copolymers. The PMMA-based random copolymer films (P(MMA-co-MHT)), block copolymer films (PMMA-b-PMHT), and PMMA-based blend films were prepared to investigate the effects of sequential structure, phase separation structure, and modification method on dielectric and energy storage properties of PMMA-based dielectric films. As a result, the random copolymer P(MMA-co-MHT) can achieve a maximum ε_r of 5.8 at 1 kHz owing to the enhanced orientation polarization and electron polarization. Because electron injection and charge transfer are limited by the strong electrostatic attraction of π-conjugated benzophenanthrene group analyzed by the density functional theory (DFT), the discharge energy density value of P(MMA-co-PMHT) containing 1 mol% MHT units with the efficiency of 80% reaches 15.00 J cm⁻³ at 872 MV m⁻¹, which is 165% higher than that of pure PMMA. This study provides a simple and effective way to fabricate the high performance of polymer dielectrics via copolymerization with the monomer of P-type semi-conductive polymer.

Herein, a high strain of ~0.3% with a small hysteresis of 43% is achieved at a low electric field of 4 kV/mm in the highly <001>-textured 0.97(0.76Bi_0.5Na_0.5TiO₃–0.24SrTiO₃)–0.03NaNbO₃ (BNT–ST–0.03NN) ceramics with an ergodic relaxor (ER) state, leading to a large normalized strain (d₃₃^*) of 720 pm/V. The introduction of NN templates into BNT–ST induces the grain orientation growth and enhances the ergodicity. The highly <001>-textured BNT–ST–0.03NN ceramics display a pure ergodic relaxor state with coexisted ferroelectric R $\overline{3}$c and antiferroelectric P4bm polar nanoregions (PNRs) on nanoscale. Moreover, due to the incomplete interdiffusion between the NN template and BNT–ST matrix, the textured ceramics present a core–shell structure with the antiferroelectric NN core, and thus the BNT-based matrix owns more R $\overline{3}$c PNRs relative to the homogeneous nontextured samples. The high <001> crystallographic texture and more R $\overline{3}$c PNRs both facilitate the relaxor-to-ferroelectric transition, leading to the low-field-driven high strain, while the ergodic relaxor state ensures a small hysteresis. Furthermore, the d₃₃^* value remains high up to 518 pm/V at 100 ℃ with an ultra-low hysteresis of 6%.