• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.3
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• pp.194-199
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• 2011

In this study, non-stoichiometric 1-x$[(K_{0.5}Na_{0.5})_{0.97}(Nb_{0.96}Sb_{0.04})O_3]$ + x $CeMnO_3$ + 0.8 mol%CuO + 0.2 wt% $Ag_2O$ (x=0, 0.005) ceramics were prepared by a conventional mixed oxide and carbonate method, their dielectric and piezoelectric properties were investigated with the variations of sintering temperature. As $CeMnO_3$ substitution incereased, the density, piezoelectric constant($d_{33}$) and dielectric constant($\varepsilon_r$) were increased and the mechanical quality factor(Qm) was decreased. At the sintering temperature of $1100^{\circ}C$, the density, electromechanical coupling factor($k_p$), dielectric constant($\varepsilon_r$) and piezoelectric constant($d_{33}$) of 0.5mol% $CeMnO_3$ specimen showed the optimun values of 4.475 $g/cm^2$, 0.437, 552 and 166 pC/N, respectively. However, the mechanical quality factor($Q_m$) showed the minimum value of 380.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.11
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• pp.2093-2096
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• 2011

In this study, lead-free $(Na_{0.5}K_{0.5})NbO_3-BiTiO_3$ ceramics were fabricated by a conventional mixed oxide method. Structural and electrical properties of lead-free $(Na_{0.5}K_{0.5})NbO_3$ ceramics with the variation of $BiTiO_3$ were investigated. The results of X-ray diffraction analysis showed a typical polycrystalline perovskite structure without presence of the second phase in all specimens. Sintered density increased with an increasing of BTO and the specimen added with 0.07 mol% of $BiTiO_3$ showed the maximum value of 97.8%. Average grain size decreased and densification increased with an increasing of $BiTiO_3$ contents. The electromechanical coupling factor of the 0.01 mol% $BiTiO_3$ doped NKN specimens was 0.32. Dielectric constant, dielectric loss and Curie temperature of the 0.07 mol% $BiTiO_3$ doped NKN specimens were 1185, 0.145% and $400^{\circ}C$, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.5
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• pp.505-512
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• 2023

This study investigated crystal structures, microstructures, and electric-field-induced strain (EFIS) properties of Bi-based lead-free ferroelectric/relaxor composites. Bi_1/2Na_0.82K_0.18)_1/2TiO₃ (BNKT) as a ferroelectric material and 0.78Bi_1/2(Na_0.78K_0.22)_1/2TiO₃-0.02LaFeO₃ (BNKT2LF) as a relaxor material were synthesized using a conventional solid-state reaction method, and the resulting BNKT2LF powders were subjected to high-energy ball milling (HEBM) after calcination. As a result, HEBM proved a larger average grain size of sintered samples compared to conventional ball milling (CBM). In addition, the increased sintering time led to grain growth. Furthermore, HEBM treatment and sintering time demonstrated a significant effect on EFIS of BNKT/BNKT2LF composites. At 6 kV/mm, 0.35% of the maximum strain (S_max) was observed in the HEBM sample sintered for 12 h. The unipolar strain curves of CBM samples were almost linear, indicating almost no phase transitions, while HEBM samples displayed phase transitions at 5~6 kV/mm for all sintering time levels, showing the highest S_max/E_max value of 700 pm/V. These results indicated that HEBM treatment with a long sintering time might significantly enhance the electromechanical strain properties of BNT-based ceramics.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.6
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• pp.489-494
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• 2009

In this study, In order to improve dielectric and piezoelectric properties of Lead-free piezoelectric ceramics, $0.95(K_{0.5}Na_{0.5})NbO_3-0.05Li(Sb_{0.8}Nb_{0.2})O_3+0.2\;wt%Ag_2O+0.4\;wt%MnO_2+Xwt%CuO$ were investigated as a function of the amount of CuO addition. With increasing the amount of CuO addition, density was increased up to 0.4 wt.% CuO and then decreased above. And also, electro mechanical coupling factor ($k_p$) was decreased. At the 0.4 wt% CuO added specimen sintered at $1020^{\circ}C$, $k_p$, Qm, density, dielectric constant (${\varepsilon}_r$) and $d_{33}$[pC/N] showed the optimal value of $4.37\;g/cm^3$, 0.354, 305, 645, and 144 pC/N respectively.

• Korean Journal of Materials Research
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• v.30 no.7
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• pp.343-349
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• 2020

NKN [(Na,K)NbO₃] is a candidate lead-free piezoelectric material to replace PZT [Pb(Zr,Ti)O₃]. A single crystal has excellent piezoelectric-properties and its properties are dependent of the crystal orientation direction. However, it is hard to fabricate a single crystal with stoichiometrically stable composition due to volatilization of sodium during the growth process. To solve this problem, a solid solution composition is designed (Na,K)NbO₃-Ba(Cu,Nb)O₃ and solid state grain growth is studied for a sizable single crystal. Ceramic powders of (Na,K)NbO₃-M(Cu,Nb)O₃ (M = Ca, Sr, Ba) are synthesized and grain growth behavior is investigated for different temperatures and times. Average normal grain sizes of individual specimens, which are heat-treated at 1,125 ℃ for 10 h, are 6.9, 2.8, and 1.6 ㎛ for M = Ca, Sr, and Ba, respectively. Depending on M, the distortion of NKN structure can be altered. XRD results show that (NKN-CaCuN: shrunken orthorhombic; NKN-SrCuN: orthorhombic; NKN-BaCuN: cubic). For the sample heat-treated at 1,125 ℃ for 10 h, the maximum grain sizes of individual specimens are measured as 40, 5, and 4,000 ㎛ for M = Ca, Sr, and Ba, respectively. This abnormal grain size is related to the partial melting temperature (NKN-CaCuN: 960 ℃; NKN-SrCuN: 971 ℃; NKN-BaCuN: 945 ℃).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.210-220
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• 2006

Dense $((Na_{0.5}K_{0.5})_{1-x}Li_x)(Nb_{0.8}Ta_{0.2})O_3$ ceramics were developed by conventional sintering process. The electrical properties of $((Na_{0.5}K_{0.5})_{1-x}Li_x)(Nb_{0.8}Ta_{0.2})O_3$ ceramics were investigated as a function of Li substitution. When the sample sintered at $1100^{\circ}C$ for 4 h with the Substitution of 2 mol% Li, electro-mechanical coupling factor ($k_p$) and piezoelectric coefficient ($d_{33}$) were found to reach the highest values of 0.42 and 210 pC/N, respectively.

• Ceramist
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• v.23 no.1
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• pp.54-88
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• 2020

Global effort has resulted in tremendous progress with energy harvesters that extract mechanical energy from ambient sources, convert it to electrical energy, and use it for systems such as wrist watches, mobile electronic devices, wireless sensor nodes, health monitoring, and biosensors. However, harvesting a single energy source only still pauses a great challenge in driving sustainable and maintenance-free monitoring and sensing devices. Over the last few years, research on high-performance mechanical energy harvesters at the micro and nanoscale has been directed toward the development of hybrid devices that either aim to harvest mechanical energy in addition to other types of energies simultaneously or to exploit multiple mechanisms to more effectively harvest mechanical energy. Herein, we appraise the rational designs for multiple energy harvesting, specifically state-of-the-art hybrid mechanical energy harvesters that employ multiple piezoelectric and triboelectric mechanisms to efficiently harvest mechanical energy. We identify the critical material parameters and device design criteria that lead to high-performance hybrid mechanical energy harvesters. Finally, we address the future perspectives and remaining challenges in the field.

• Korean Journal of Materials Research
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• v.25 no.7
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• pp.317-321
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• 2015

The effects of Nb doping on the crystal structure, microstructure, and dielectric ferroelectric and piezoelectric properties of $(Bi_{0.5}Na_{0.5})_{0.935}Ba_{0.065}Ti_{(1-x)}Nb_xO_3-0.01SrZrO_3$ (BNBTNb-SZ, with ${\chi}=0$, 0.01 and 0.02) ceramics have been investigated. X-ray diffraction patterns revealed that all ceramics have a pure perovskite structure with tetragonal symmetry. The grain size of the ceramics slightly decreased and a change in grain morphology from square to spherical shape was observed in the Nb-doped samples. The maximum dielectric constant temperature ($T_m$) increases with increasing amount of Nb; however, ferroelectric-relaxor transition temperature ($T_{F-R}$) and maximum dielectric constant (${\varepsilon}_m$) values decrease gradually. Nb addition disrupted the polarization hysteresis loops of the BNBT-SZ ceramics by leading a reduction in the remnant polarization coercive field and piezoelectric constant.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.1 no.2
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• pp.27-32
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• 2008

A current research basically diverted towards an increase in the operational output with the minimization of the materials used, which ultimately scaled down the dimensions of ceramic electronic components. In this direction the nano-technology pave the revolutionary changes in particular the electronic industries. The applications of nano-sized particles or nano-sized materials are hence, playing a significant role for various purposes. The PZT(lead, zirconium, titanium) based ceramics which, are reported to be ferroelectric materials have their important applications in the areas of surface acoustic waves (SAW), filters, infrared detectors, actuators, ferroelectric random access memory, speakers, electronic switches etc. Moreover, these PZT materials possess the large electro mechanical coupling factor, large spontaneous polarization, low dielectric loss and low internal stress etc. Hence, keeping in view the unique properties of PZT piezoelectric ceramics we also tried to synthesize indigenously the small sized PZT ceramic powder in the laboratory by using the modified sol-gel approach. In this paper, propyl alcohol based sol-gel method was used for preparation of PZT piezoelectric ceramic. The powder obtained by this sol-gel process was calcined and sintering to reach a pyrochlore-free crystal phase. The characterization of synthesized material was carried out by the XRD analysis and the surface morphology was determined by high resolution scanning electron microscopy.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.6
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• pp.342-347
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• 2016

We investigated the effect of $Bi_{1/2}(Na_{0.82}K_{0.18})_{1/2}TiO_3$ (BNKT) modification on the ferroelectric and electric-field-induced strain (EFIS) properties of lead-free $0.97Bi_{1/2}(Na_{0.82}K_{0.18})_{1/2}TiO_3-0.03LaFeO_3$ (BNKTLF) ceramics as a function of BNKT content (x= 0, 0.1, 0.2, 0.3, 0.5, and 1). BNKT-modified BNKTLF powders were synthesized using a conventional solid-state reaction method. As the BNKT content x increased from 0 to 1 the normalized electric-field-induced strain ($S_{max}/E_{max}$) was observed to increase at relatively low fields, i.e., below the poling field. Moreover, BNKTLF-30BNKT showed about 460 pm/V as low as at 3 kV/mm, which is a considerably high value among the lead-free systems reported so far. Consequently, it was confirmed that ceramic-ceramic composite, a mixture of an ergodic relaxor matrix and embedded ferroelectric seeds, is a salient way to make lead-free piezoelectrics practical with enhanced EFIS at low field as well as less hysterical.