Synergistic optimization of structures and properties in NBT ceramics via heterovalent ion substitution at B‐site

Abstract Na 0.5 Bi 4.5 Ti 4 O 15 (NBT), a representative Aurivillius‐type ferroelectric materials, shows great promise for high‐temperature piezoelectric applications. However, both large piezoelectric coefficient ( d 33 ) and high Curie temperature ( T C ) are rather hard to achieve in NBT. In this study, an A/B‐site co‐substitution strategy was used for synergistically optimizing the structures and properties of NBT, a series of polycrystalline ceramics with chemical formula of (NaBi) 0.48 (KMn) 0.02 Ti 3.98 D 0.02 O 15 (D: Gd, Ce, Nb, W) were synthesized via a conventional solid‐state method. The influences of B‐site substitution ions with different chemical valences on the lattice/grain structures and dielectric/ferroelectric/piezoelectric properties, as well as alternating current (AC) impedance characteristics, were systematically studied. Nb⁵⁺ substitution notably enhanced the non‐centrosymmetric degree of lattice by inducing TiO 6 octahedral distortion and promoted domain wall motion, leading to the synergistic enhancement in piezoelectric activity and thermal stability. Nb⁵⁺ substitution also facilitated the grain growth of NBT, whereas both Gd 3+ and Ce 4+ substitution suppressed it. Unexpectedly, W 6+ substitution increased the oxygen vacancy concentration of NBT, resulting in an increased conductivity at high temperature. On the other hand, the donor substitution of Nb 5+ or W 6+ for Ti 4+ favored the relaxation processes of charge carriers in NBT at elevated temperatures, resulting in improved dielectric dynamics. Among them, the NBKMT‐Nb ceramic achieved the highest T C (668°C) and the largest d 33 (29 pC/N), as well as the lowest tan δ (0.16%). Also, it exhibited a better thermal stability than others ( d 33 remained 70% of its initial value after annealing at 600°C for 4 h). This study not only provided insight into the role of heterovalent substitution ions in optimizing the structures and properties of NBT, but also offered a strategy for designing the high‐performance Aurivillius‐phase ceramics.