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.
Compared to the bulk-CN, the quasi-2D-CN possesses a unique electronic structure, enlarged bandgap, prolonged lifetime, increased surface area and enhanced electronic transport, and exhibits highly efficient hydrogen production from water under visible light.
Schematic diagram of the proposed gas-sensing mechanism for the p-type BiFeO3 based gas sensor: (a) and (c) in air, (b) and (d) in reducing gas, (e) simplified equivalent circuit.
Ternary solid solutions of (1 -x)(0.8Bi 0.5 Na 0.5 TiO 3 -0.2Bi 0.5 K 0.5 TiO 3 )-xNaNbO 3 (BNKT-xNN) lead-free piezoceramics were fabricated using a conventional solid-state reaction method. Pure BNKT composition exhibited an electric-fieldinduced irreversible structural transition from pseudocubic to ferroelectric rhombohedral phase at room temperature. Accompanied with the ferroelectric-to-relaxor temperature T F-R shifted down below room temperature as the substitution of NN, a compositionally induced nonergodic-to-ergodic relaxor transition was presented, which featured the pinched-shape polarization and sprout-shape strain hysteresis loops. A strain value of~0.445% (under a driving field of 55 kV/cm) with large normalized strain of~810 pm/V was obtained for the composition of BNKT-0.04NN, and the large strain was attributed to the reversible electric-field-induced transition between ergodic relaxor and ferroelectric phase.
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