• Journal of the Korean Ceramic Society
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• v.54 no.2
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• pp.86-95
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• 2017

Active search for lead-free piezoceramics over the last decade has harvested a considerable amount of achievements both in theory and in practice. Few would deny that those achievements are highly beneficial, but agree that this quest of developing the lead-free piezoceramics in replace for PZTs is successfully completed. Nevertheless, few would clearly state where this quest should be directed in our next move. A source of this uncertainty may originate from the fact that it is still not clear how good is good enough to beat PZTs. In this short review, we analyzed the existing literature data to clearly locate the current state of the art of lead-free piezoceramics in comparison to PZT-based piezoceramics. Four strategies of a potential importance were suggested and discussed to help researchers plan and design their future research on lead-free piezoceramics with a recently reported exemplary work.

• Journal of Sensor Science and Technology
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• v.30 no.6
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• pp.408-414
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• 2021

This study analyzes the phase transition behavior and electrical properties of lead-free (1-x)K_0.5Na_0.5NbO₃-xBaZrO₃ (KNN-100xBZ) piezoelectric ceramics. The stabilized crystal structures in BaZrO₃-modified KNN ceramics is clarified to be pseudocubic. The polymorphic phase transition from the orthorhombic to pseudocubic phases can be observed with KNN-6BZ ceramics considering the optimized piezoelectric constant (d₃₃). Electromechanical strain behaviors are discussed. Accordingly, the enhancement of strain value at x = 0.08 (composition) may originate from the coexistence of ferroelectric domains and polar nanoregions. A schematic of domains for KNN, KNN-8BZ, and KNN-15BZ ceramics has been proposed to describe the relationship between the stabilized relaxor and changes in electrical properties.

• Proceedings of the Materials Research Society of Korea Conference
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• 2007.11a
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• pp.97.2-97.2
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• 2007

• Journal of the Korean Ceramic Society
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• v.56 no.6
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• pp.549-557
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• 2019

More than two decades of world-wide research efforts have resulted in several classes of potentially important materials. Among them are incipient piezoelectrics, which are especially useful for actuator applications. However, relatively large electric fields are required for activating the large incipient electromechanical strains. So far, many attempts have been made to reduce the required electric field by intentionally inhomogenizing the electric field distribution in the microstructure through core-shell and composite approaches. Here, we show that electric field concentration can be realized simply by adjusting electrode patterns. We have investigated the effect of electrode patterning on the incipient electromechanical strain properties of an exemplarily chosen lead-free relaxor system, revealing that electrode patterning does have a significant role on the strain properties of the given lead-free relaxor system. We believe that this approach would make a new strategy for ones to consider bringing the functional properties of electroceramics beyond their conventional limit.

• Journal of the Korean Ceramic Society
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• v.50 no.2
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• pp.157-162
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• 2013

The need for lead-free piezoceramics has caused a renewal of interest in $BaTiO_3$-based systems. Recently, it was found that ceramics in the $(Ba,Ca)(Zr,Ti)O_3$ system have properties comparable to those of $Pb(Zr,Ti)O_3$. However, these ceramics require rather high sintering temperatures of $1450-1550^{\circ}C$. In this work, the effect of $TiO_2$ and CuO addition on the sintering behavior, microstructure, dielectric and piezoelectric properties of $(Ba_{0.85}Ca_{0.15})(Zr_{0.1}Ti_{0.9})O_3$ (BCTZ) ceramics will be discussed. BCTZ ceramics were prepared by the mixed oxide route and 1 mol % of $TiO_2$ or CuO was added. Undoped and doped ceramics were sintered at $1350^{\circ}C$ for 1-5 h. CuO was found to be a very effective sintering aid, with samples sintered for 1 h at $1350^{\circ}C$ having a bulk density of 95% theoretical density; however the piezoelectric properties were greatly reduced, probably due to the small grain size.

• Journal of Sensor Science and Technology
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• v.24 no.4
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• pp.228-231
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• 2015

Ultrasonic motors provide high torques and quick responses compared to their magnetic counterparts; therefore, they are widely used in small-scale applications such as mobile phones, microrobots, and auto-focusing modules in digital cameras. To determine the feasibility of lead-free piezoceramics for ultrasonic motor applications, we fabricated a ring-type piezoceramic with a KNN-based lead-free piezoceramic (referred to as CZ5), intended for use in an auto-focusing module of a digital camera. The vibration of the lead-free stator was observed at 45.1 kHz. It is noteworthy that the fully assembled lead-free ultrasonic motor exhibited a revolution speed of 5-7 rpm, even though impedance matching with neighboring components was not considered. This result suggests that the tested KNN-based piezoceramic has great potential for use in ultrasonic motor applications, requiring minimal modifications to existing lead-based systems.

• Korean Journal of Materials Research
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• v.31 no.10
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• pp.562-568
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• 2021

(Bi_1/2Na_1/2)TiO₃ (BNT)-based ceramics are considered promising candidates for actuator application owing to their excellent electromechanical strain properties However, to obtain large strain properties, there remain several issues such as thermal stability and high operating fields. Therefore, this study investigates a reduction of operating field in (0.98-x)Bi_1/2Na_1/2TiO₃-0.02 BiAlO₃-xSrTiO₃ (BNT-2BA-100xST, x = 0.20, 0.21, 0.22, 0.23, and 0.24) via analyses of the microstructure, crystal structure, dielectric, polarization, ferroelectric and electromechanical strain properties. The average grain size of BNT-${\underline{2}}$BA-100xST ceramics decreases with increasing ST content. Results of polarization and electromechanical strain properties indicate that a ferroelectric to relaxor state transition is induced by ST modification. As a consequence, a large electromechanical strain of 592 pm/V is obtained at a relatively low electric field of 4 kV/mm in 22 mol% ST-modified BNT-2BA ceramics. We believe that the materials synthesized in this study are promising candidates for actuator applications.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.35 no.1
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• pp.24-31
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• 2022

This study investigated microstructures, crystal structures, polarization, dielectric and electromechanical properties of 0.76Bi_1/2Na_1/2TiO₃-0.24SrTiO₃ (BNT-24ST)-based piezoceramcs by adding Li₂CO₃ and B₂O₃ (LB) as sintering aids for low-temperature sintering. All samples were successfully synthesized using conventional solid-state reaction method and sintered at 950, 1,000, 1,050, 1,100 and 1,175℃ for 2 hours. Without LB, specimens required sintering temperatures over 1,175℃ for sufficient densification, while the addition of 0.10-mol LB decreased the sintering temperatures down to 950℃. The average grain size and dielectric properties of BNT-24ST-10LB ceramics were enhanced with increasing sintering temperature. We found that the low-temperature sintered BNT-24ST piezoceramics by adding LB showed the d₃₃*value of 402 pm/V at 4 kV/mm after sintering at 1,050℃, which was better than that of high-temperature fired specimens sintered at 1,175℃ without LB (242 pm/V). We believe that the results of this study promise a candidate for low-cost multilayer ceramic actuator applications.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.34 no.1
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• pp.1-7
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• 2021

This study investigated the structural, dielectric, ferroelectric, and strain properties of (0.98-x)Bi1/2Na1/2TiO3-0.02BiFeO3-xSrTiO3 (BNT-BF-100xST, x＝0.20, 0.22, 0.24, 0.26, and 0.28). All samples were successfully synthesized using the conventional solid-state reaction method and sintered at 1,175℃ for 2 h. The average grain size of the BNT-BF-100x ceramics decreased with increasing ST content. Furthermore, we observed that the ferroelectric- relaxor transition temperature (TF-R) decreased with increasing ST content, which eventually vanished in the BNT-BF-24ST ceramics. The results indicated that a ferroelectric to relaxor phase transition could be induced by ST modification. Consequently, a large electromechanical strain of 633 pm/V at 4 kV/mm was observed for the BNT-BF-26ST ceramics. These results imply that our materials have the competitive advantage of larger strain under lower operating field conditions compared with other BNT-based lead-free piezoelectric ceramics. We expect that BNT-BF-ST lead-free piezoelectric ceramics are promising candidates as a novel ternary BNT-based system and can find potential applications in actuators.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.9
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• pp.646-650
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• 2013

$(Na,K)NbO_3$-based piezoelectric ceramics were synthesized by a liquid phase sintering method with a selected glass frit. The effects of the content of the glass frit and the sintering temperature on the microstructure and the electrical properties of the samples were investigated. With the 0.1 wt% of glass frit content, $(Na_{0.52}K_{0.44}Li_{0.06})(Nb_{0.84}Ta_{0.10}Sb_{0.06})O_3$ (NKL-NTS) ceramics showed the maximum values of the relative density (99.1%) and the electro-mechanical coupling factor ($k_p$: 0.32) at the sintering temperature of $1,050^{\circ}C$. It might mean that a liquid phase sintering with a suitable glass frit having the lower flow temperature could improve the relative density and the piezoelectric properties.