Piezoelectric properties of (Na_0.5K_0.5)(Nb_1‐xSb_x)O₃‐SrTiO₃ ceramics with tetragonal‐pseudocubic PPB structure

Abstract

CuO‐added 0.96(Na0.5K0.5)(Nb1‐xSbx)O3‐0.04SrTiO3 ceramics sintered at the low temperature of 960°C for 10 hours showed dense microstructures and high relative densities. The specimens with 0.0 ≤ x ≤ 0.04 had orthorhombic‐tetragonal polymorphic phase boundary (PPB) structure. Tetragonal‐pseudocubic PPB structure was observed in specimens with 0.05 ≤ x ≤ 0.07, while the specimen with x = 0.08 has a pseudocubic structure. The structural variation in the specimens is explained by the decreases in the orthorhombic‐tetragonal transition temperature and Curie temperature with the addition of Sb5+ ions. The specimens with 0.05 ≤ x ≤ 0.07, which have tetragonal‐pseudocubic PPB structure, had large electric field‐induced strains of 0.14%‐0.016%. Moreover, these specimens also showed increased d33 values between 280 pC/N and 358 pC/N. In particular, the specimen with x = 0.055 showed particularly enhanced piezoelectric properties: d33 of 358 pC/N, kp of 0.45, and the electric field‐induced strain of 0.16% at 4.5 kV/mm.

Recent Developments in (K, Na)NbO3-Based Lead-Free Piezoceramics

“…Moreover, a pseudocubic (PC) structure was observed at temperatures near T C [ 77 , 78 , 79 ]. The PC structure cannot be considered as a cubic (C) structure because a KNN-modified ceramic with a pure PC structure exhibits piezoelectric properties [ 80 ]. Therefore, a PC structure was interpreted as an R structure or the T–C multistructure based on Rietveld analysis [ 77 , 78 , 79 , 80 ].…”

“…The PC structure cannot be considered as a cubic (C) structure because a KNN-modified ceramic with a pure PC structure exhibits piezoelectric properties [ 80 ]. Therefore, a PC structure was interpreted as an R structure or the T–C multistructure based on Rietveld analysis [ 77 , 78 , 79 , 80 ]. In addition, the PC structure has been understood as various structures depending on the specimens in which the PC structure is developed.…”

“…Therefore, it is difficult to suggest the unique atomic model for the PC structure developed in the KNN-modified piezoceramics. However, since detailed information on the PC structure was reported in previous studies [ 77 , 78 , 79 , 80 , 81 , 82 ], the various atomic model diagrams for the PC structure can be obtained using the information reported in the previous studies. KNN-modified lead-free piezoceramics started gaining interest at the beginning of this century and increased considerably after Satio et al reported that KNN-modified ceramics fabricated by the reactive template grain growth (RTGG) technique provided a high d 33 of 416 pC/N [ 83 ].…”

“…Finally, KNN-based ceramics with an O–PC or T–PC multistructure were developed by reducing T C near RT, providing a slightly improved d 33 value of ~330 pC/N. The composition and piezoelectric properties of KNN-modified piezoceramics, in which the two structures coexist, were reviewed in a previous study [ 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 ].…”

Dependence of Phase Structure and Discharge Performance on the Temperature of Perovskite Composited Ceramics

“…[21] In addition, KNN is a ferroelectric material with a higher Curie temperature, which can effectively improve temperature stability. [22,23] Chai et al [24] reported that KNN, as a transparent ferroelectric material, can effectively improve the energy storage density, so it is feasible for KNN ceramics to be used in pulse capacitors.…”