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19. Thermally stable large strain in low‐loss (Na0.2K0.8)NbO3‐BaZrO3 for multilayer actuators.

Author

Kim, Sun‐Woo, Lee, Tae‐Gon, Kim, Dae‐Hyeon, Kim, Eun‐Ji, Kim, Dae Su, Kang, Woo‐Seok, Jo, Wook, Lee, Sang Jin, Han, Seung Ho, Kang, Hyung‐Won, Hong, Youn‐Woo, and Nahm, Sahn

Subjects
PIEZOELECTRIC actuators, THERMAL fatigue, ACTUATORS, DIELECTRIC loss, THERMAL properties, THERMAL strain
Abstract

CuO‐doped (1–x)(Na0.2K0.8)NbO3‐xBaZrO3 ceramics (0.0 ≤ x ≤ 0.06) were densified at 960°C. The ceramic with x = 0 exhibited a large sprout‐shaped strain vs electric‐field (S‐E) curve and a double polarization vs electric‐field (P‐E) hysteresis curve, owing to the defect polarization (PD) developed between Cu2+ ions at Nb5+ sites and oxygen vacancies. The sizes of the S‐E and P‐E loops decreased with increasing x, owing to the decrease in the number of PDs. The ceramic with x = 0.04 displayed small S‐E and P‐E curves, indicating its small dielectric loss. It exhibited large strain (0.19% at 8.0 kV/mm) at room temperature, which was maintained at 200°C. A similar strain was observed after applying 106 cycles of an electric field (3.0 kV/mm). Hence, this specimen exhibited large strain with excellent thermal and fatigue properties. Moreover, the synthesized multilayer actuator using the ceramic with x = 0.04 showed excellent vibrational properties, making it promising for applications in multilayer piezoelectric actuators. [ABSTRACT FROM AUTHOR]

Published
2019
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32. Effect of chemical inhomogeneity on domains and ferroelectric properties of Fe‐modified 0.77Bi0.5Na0.5TiO3–0.23SrTiO3.

Author

Cho, Jeong‐Ho, Jeong, Seung‐Jae, Kim, Sung‐Won, Jeon, Chang‐Jun, Jeong, Young‐Hun, Yun, Ji‐Sun, Hong, Youn‐Woo, and Paik, Jong‐Hoo

Subjects
BISMUTH compounds, TITANIUM compounds, STRONTIUM compounds, ENERGY dispersive X-ray spectroscopy, SCANNING transmission electron microscopy
Abstract

Abstract: Lead‐free 0.77(Bi0.5Na0.5)TiO3–0.23Sr(Ti1−xFex)O3 (x = 0, 0.04) (BNT–23STFx) was prepared using a conventional solid‐state reaction route. The effects of Fe‐modification on the chemical homogeneity from a μm scale perspective, the core‐shell domains structures, and the ferroelectric properties were investigated. The chemical homogeneity was analyzed using energy dispersive X‐ray mapping in scanning transmission electron microscopy mode, and the field‐dependent behaviors of strain and polarization were obtained to determine the ferroelectric properties. Substituting Fe3+ for Ti4+ resulted in completely different electrical behavior and properties, despite similar XRD patterns and microstructures. The Fe‐substitution promoted the mobility of Sr2+ ions in the BNT phase and, as a consequence, the chemical homogeneity increased and the core‐domains collapsed. Extending the ceramic processing, such as milling time and sintering time, affected domain distribution and compositional inhomogeneity, which led to a gradual transformation from ferroelectric to relaxor. [ABSTRACT FROM AUTHOR]

Published
2018
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36. Piezoelectric properties of (Na0.5K0.5)(Nb1‐xSbx)O3‐SrTiO3 ceramics with tetragonal‐pseudocubic PPB structure.

Author

Kim, Dae‐Hyeon, Lee, Tae‐Gon, Cho, Sung‐Hoon, Lee, Ku‐Tak, Lee, Tae‐Ho, Hong, Youn‐Woo, Hong, Chang‐Hyo, Kim, Jeong‐Seog, and Nahm, Sahn

Subjects
PIEZOELECTRIC materials, CERAMIC materials, SINTERING, ORTHORHOMBIC crystal system, TRANSITION temperature, CURIE temperature, PIEZOELECTRICITY
Abstract

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. [ABSTRACT FROM AUTHOR]

Published
2018
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