High strain with low hysteresis is crucial for commercial applications in high precision actuators. However, the clear conflict between the high strain and low hysteresis in BNT-based ceramics has long been an obstacle to actual precise actuating or positioning applications. To obtain piezoceramics with high strain and low hysteresis, it is necessary to enhance the electrostrictive effect and develop an ergodic relaxor (ER) and nonergodic relaxor (NR) phase boundary under ambient conditions. In this work, (Co_0.5Nb_0.5)⁴⁺ doped 76Bi_0.5Na_0.5TiO₃-24SrTiO₃ (BNST24) relaxors were fabricated using the conventional solid state reaction route. X-ray diffraction patterns revealed the B-site substitution in BNST24 ceramics. By adjusting the (Co_0.5Nb_0.5)⁴⁺ doping in BNST24, we effectively tuned the T_NR-ER and T_d close to ambient temperature, which contributed to the development of the ergodic relaxor phase and enhanced the electrostrictive effect at ambient temperature. The I-P-E loops and bipolar strain curves verified the gradual evolution from NR to ER states, while the enhanced electrostrictive effect was verified by the nearly linear S-P² curves and improved electrostrictive coefficient of the BNST24-xCN relaxors. An enhanced strain of 0.34% (d^*₃₃ = 483 pm/V) with low hysteresis of 8.9% was simultaneously achieved in the BNST24-0.02CN relaxors. The enhanced strain was mainly attributed to the proximity effect at the ER and NR phase boundary of BNST24-0.02CN, while the improved electrostrictive effect contributed to the reduced strain hysteresis. Our work demonstrates an effective strategy for balancing the paradox of high strain and low hysteresis in piezoceramics.

Polymeric positive temperature coefficient (PTC) materials with low switching temperature points are crucial for numerous electronic devices, which typically function within the room temperature range (0–40 °C). Ideal polymeric PTC materials for flexible electronic thermal control should possess a room-temperature switching temperature, low room-temperature resistivity, exceptional mechanical flexibility, and adaptive thermal control properties. In this study, a novel PTC material with a room-temperature switching temperature and superb mechanical properties has been designed. A blend of a semi-crystalline polymer EVA with a low melting temperature (Tm) and an amorphous polymer (PVAc) with a low glass transition temperature (Tg) was prepared. Low-cost graphite was chosen as the conductive filler, while CNF was incorporated as a hybrid filler to enhance the material’s heating stability. PVAc0.4/EVA0.6/GP-3wt.% CNF exhibited the lowest room temperature resistivity, and its PTC strength (1.1) was comparable to that without CNF addition, with a Curie temperature of 29.4 °C. Room temperature Joule heating tests revealed that PVAc0.4/EVA0.6/GP-3wt.% CNF achieved an equilibrium temperature of approximately 42 °C at 25 V, with a heating power of 3.04 W and a power density of 3.04 W/cm². The Young’s modulus of PVAc0.4/EVA0.6/GP-3wt.% CNF was 9.24 MPa, and the toughness value was 1.68 MJ/m³, indicating that the elasticity and toughness of the composites were enhanced after mixing the fillers, and the mechanical properties of the composites were improved by blending graphite with CNF.