Mapping the low tolerance factor Bi(Li1/3Zr2/3)O3 end member and MPB composition nexus in Bi1/2Na1/2TiO3-based ceramics

Abstract

The structural stability of an end member Bi(Li1/3Zr2/3)O3 was calculated by a first principal method and lead-free perovskite piezoelectric system (1 − x)Bi1/2Na1/2TiO3-xBi(Li1/3Zr2/3)O3 (0 ≤ x ≤ 0.05 [(1 − x)BNT-xBLZ] was synthesized. Rietveld analysis of the XRD data shows the coexistence of rhombohedral (R3c) and tetragonal (P4bm) phases for the compositions (x = 0.01 and 0.02). A remarkable shift in the transition temperature (TF-R) below room temperature was observed with increasing BLZ content. In the vicinity of the coexistence between rhombohedral and tetragonal phases, the sample with x = 0.02 exhibits enhanced remnant polarization (Pr ∼ 34 µC/cm2) and an optimal direct piezoelectric coefficient (d33 ∼ 107 pC/N) attributed to the reduction of energy barriers for polarization switching. However, further addition of BLZ manifested a coexistence of nonergodic and ergodic relaxor phases at or near room temperature, particularly for the x = 0.03 composition, which exhibits a maximum electrostrain of 0.13 % with normalized strain (Smax/Emax = 173 pm/V). Furthermore, a relationship between the tolerance factor (t) of end members and the morphotropic phase boundary (MPB) compositions was explored, which provides valuable insight into the specific range of tolerance factors for MPB compositions. It was found that the t value associated with the formation of the MPB is confined to a relatively narrow range (t = 0.9750–0.9757) in (1 − x)BNT-xBi(M1M2)O3 systems featuring low tolerance factor end members. These findings offer a valuable reference point for swiftly identifying the approximate region where the MPB is likely to occur in newly designed solid solutions. © 2024