Giant strain with low hysteresis in A-site-deficient (Bi0.5Na0.5)TiO3-based lead-free piezoceramics

Abstract

We report a giant strain (0.72 %) with a low degree of hysteresis (ca. 36.2 %) and a giant S max /E max ratio (916 pm V-1 , S max and E max denote the maximum strain and the corresponding electric field, respectively) for lead-free (1-x)(0.8Bi 0.5 Na 0.5 TiO 3-0.2Bi 0.5 K 0.5 TiO 3)-xSr 0.8 Bi 0.1 □ 0.1 Ti 0.8 Zr 0.2 O 2.95 piezoceramics with x = 0.06. The giant strain originates from a reversible transition between the ergodic relaxor and ferroelectric states under applied electric fields. A-site vacancies (V A) and oxygen vacancies (V O), deliberately introduced to the system, induce a randomly distributed local polarization field. The local field induces embryonic polarization domains that have a broad distribution of maturity and thus smears the transition between the ferroelectric and relaxor states. This leads to a narrow hysteresis loop. The poling field required for the relaxor-to-ferroelectric transition is reduced significantly, due to the remanent ferroelectric phase at zero field acting as the seed, and the point defects synergistically facilitating the nucleation and growth of the ferroelectric phase. Our work provides a novel route for designing piezoelectric materials with both a giant strain and a narrow hysteresis for practical actuator applications.

Large strain response with low driving field in Bi1/2Na1/2TiO3–Bi1/2K1/2TiO3–Bi(Mg2/3Nb1/3)O3 ceramics

“…The S ‐ E loop exhibits pronounced hysteretic behavior as well, suggesting the large strain is induced mainly by extrinsic effects instead of true piezoelectric response . Generally, the giant strain is mostly attributed to the existence of nonpolar phase at zero external electric field . Compositional‐dependent unipolar strain loops are shown in Figure B.…”

Lead-free Bi(Mg0.5Ti0.5)O3-modified 0.875Bi0.5Na0.5TiO3-0.125BaTiO3 ferroelectric ceramics with tetragonal structure and large field-induced strains

“…When BT content exceeds over 10 mol.%, the solid solution possesses tetragonal structure with P4mm space group at room temperature, and then transforms into ergodic relaxor P4bm space group at temperature T F-R . 12,13 However, the field-induced strain behavior of tetragonal NBT-BT compositions was rarely considered.…”

Reduced leakage current and enhanced piezoelectricity of BNT–BT–BMO thin films

“…The variation of S / E can be attributed to the following factors. First of all, in BNT‐based systems, a bias field could induce a transition of a relaxor phase to a ferroelectric phase, and this process is reversible . Since the diffuseness of the BNT–BT–0.01BMO thin film is the highest among all thin films, ergodic relaxation can help the system switch back from its original state, leading to a large reversible strain .…”