Correlation between depolarization temperature and lattice distortion in quenched (Bi_1/2Na_1/2)TiO₃-based ceramics

Abstract

(Bi1/2Na1/2)TiO3 (BNT) is one of the candidates for lead-free piezoelectric ceramics. Recently, we found that the depolarization temperature T d of BNT could be increased by approximately 40 °C–80 °C with a quenching treatment after the sintering. To elucidate the mechanism, high-energy synchrotron X-ray powder diffraction data were collected in SPring-8 to analyze their crystal structures in detail. In the case of a quenched BNT-based sample, Bi ions displaced more to the off-center position of the A-site in a perovskite structure with a more ordered structure. The increase in rhombohedral distortion then affects the T d elevation in the quenched sample.

Quenching effects on depolarization temperature and ¹⁸O tracer diffusion in (Bi_0.5Na_0.5)TiO₃ ceramics with acceptor and donor additives

“…In the quenched samples, previous reports reveal that the enhancement of lattice distortion enhances the order of the lattice structure and then stabilizes the structural phase. 29) Our results (Fig. 7) also showed that the lattice distortion was enhanced by quenching, and we considered that the lattice of the quenched samples has a more ordered structure than that of OF-samples.…”

“…16) Such a contribution of the bonding enhances disorder in the lattice, and then the structural phase of the unit cell changes from R3c to P4bm or Pnma. 16),17),27) 29) The quenching process after sintering is effective to increase the T d of BNT ceramics with the rhombohedral phase and the quenching does not deteriorate their piezoelectric and ferroelectric properties. 30), 31) The T d of BNT ceramics reaches 223°C after quenching from 1100°C, that is, the T d is about 50°C higher than that by the conventional cooling process.…”

“…36)38) Quenching freezes the off-centered structure and stabilizes the R3c structure. 29) On the other hand, recently, the Ti off-center has been demonstrated by local structural analysis. 39) Both of these reports showed that the order of the crystal structure is commonly enhanced by the quenching process.…”

Quenching‐circumvented ergodicity in relaxor Na1/2Bi1/2TiO3‐BaTiO3‐K0.5Na0.5NbO3

“…41 In NBT-6BT, it has been demonstrated that Bi-O and Bi-Ti bond distances feature an abrupt change at T m but not at T F-R , indicating the transformation from rhombohedral to tetragonal phase to occur gradually. However, a recent report indicated that quenching results in enhanced Bi 3+ offcentering as opposed to furnace-cooled specimens, 32 which can alter the local structure. In the present work, it was observed that quenching significantly affects T F-R , but does not alter T m (Figure 3; Table 1) and the quenched compositions exhibit an increased tetragonal distortion.…”

Morphotropic Phase Boundary on K-substituted Na_0.5Bi_0.5TiO₃ Synthesized with Suppressing Evaporation of Bismuth and Sodium

“…The unit-cell parameters of K-substituted NBTs were refined by Rietveld analysis and summarized in Table I. Larger isotropic atomic displacement parameters, B, of Na, Bi and K sites may be caused by the displacement of Bi ions on the off-center position along the <111> direction [20].…”