• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.5
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• pp.355-359
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• 2013

In this paper, the $0.995(Li_{0.04}(Na_{0.56}K_{0.44})_{0.96}(Nb_{0.90}Ta_{0.10})_{0.998}Zn_{0.005}O_3+0.005KNbO_3+xwt%\;TeO_2$ lead-free piezoelectric ceramics for energy harvesting devices were fabricated by the conventional mixed oxide method. The microstructure, dielectric, and piezoelectric properties were investigated as a function of the $TeO_2$ addition. All the specimens showed an orthorhombic phase structure. At the composition ceramics doped with 0.1 wt%$TeO_2$, the optimum values of $d_{33}$= 212 pC/N, $d_{33}{\cdot}g_{33}=9.54pm^2/N$, and kp=0.448 were obtained, respectively. The results indicate that the composition ceramics is a promising candidate for energy harvesting devices applications.

• Korean Journal of Materials Research
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• v.28 no.9
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• pp.489-494
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• 2018

Lead free $(1-x)(0.675BiFeO_3-0.325BaTiO_3)-xLiTaO_3$ (BFBTLT, x = 0, 0.01, 0.02, and 0.03, with 0.6 mol% $MnO_2$ and 0.4 mol% CuO) were prepared by a solid state reaction method, followed by air quenching and their crystalline phase, morphology, dielectric, ferroelectric and piezoelectric properties were explored. An X-ray diffraction study indicates that lithium (Li) and tantalum (Ta) were fully incorporated in the BFBT materials with the absence of any secondary phases. Dense ceramic samples (> 92 %) with a wide range of grain sizes from $3.70{\mu}m$ to $1.82{\mu}m$ were obtained in the selected compositions ($0{\leq}x{\leq}0.03$) of BFBTLT system. The maximum temperatures ($T_{max}$) were mostly higher than $420^{\circ}C$ in the studied composition range. The maximum values of maximum polarization ($P_{max}{\approx}31.01{\mu}C/cm^2$), remnant polarization ($P_{rem}{\approx}22.82{\mu}C/cm^2$) and static piezoelectric constant ($d_{33}{\approx}145pC/N$) were obtained at BFBT-0.01LT composition with 0.6 mol% $MnO_2$ and 0.4 mol% CuO. This study demonstrates that the high $T_{max}$ and $d_{33}$ for BFBTLT ceramics are favorable for industrial applications.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.9
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• pp.728-732
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• 2011

In this study, piezoelectric and dielectric properties of Lead-free $0.97[(K_{0.5}Na_{0.5})(Nb_{0.97}Sb_{0.03})O_3]+0.03[(Bi_{0.5}K_{0.5})TiO_3]$ (abbreviated as 0.97NKNS-0.03BKT)ceramics synthesized by conventional solid-state reaction process were investigated as a function of $K_{5.4}Cu_{1.3}Ta_{10}O_{29}$ addition. The results indicated that the $K_{5.4}Cu_{1.3}Ta_{10}O_{29}$ addition significantly improved the sinterability, grain growth and piezoelctric properties of 0.97NKNS-0.03BKT ceramics. The optimum values as planar piezoelectric coupling coefficient ($k_p$= 0.355), piezoelectric constant ($d_{33}$= 207 pC/N) and mechanical quality factor ($Q_m$= 128) were obtained when 0.009KCT was added. The electromechanical coupling factor($k_p$) was slightly decreased according to the increasing temperature.

• 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.29 no.4
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• pp.205-209
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• 2016

In this paper, piezoelectric ceramics with the composition of $(Na_{0.525}K_{0.4425}Li_{0.0375})(Nb_{0.8975}Sb_{0.065}Ta_{0.0375})O_3+0.3wt%\;CoO+x\;CuO$ ($0.005{\leq}x{\leq}0.025$) (abbreviated to NKL-NST) were fabricated for ultrasonic sensor application. The effects of CuO addition and sintering on the microstructure and the piezoelectric properties of the NKL-NST ceramics were systematically studied. Excellent piezoelectric properties such as electromchanical coupling $factor(k_p)=0.415$, piezoelectric constant $(d_{33})=166pC/N$ and piezoelectric figure of merit $d_{{33}*}g_{33}=5.47pm^2/N$ were obtained from the 2.5 mol% CuO doped NKL-NST+0.3 wt%CoO ceramics sintered at $1,000^{\circ}C$ for 3 h.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.660-663
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• 2003

In this Study, lead-free $Bi_{0.5}(Na_{0.84}K_{0.16})_{0.5}TiO_3$ system ceramics were fabricated with the variations of Sr substitution and their dielectric and piezoelectric characteristics were investigated. With the increase of Sr substitution, dielectric constant increased linearly and Curie temperature decreased slightly. Also, the temperature dependence curve of dielectric constant was moved to left-ward. At 4mol% Sr substitution, Tc of 292, kp of 34.03%, kt of 45.32% and ${\epsilon}r$ of 868 were shown, respectively.

• Transactions on Electrical and Electronic Materials
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• v.18 no.1
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• pp.1-6
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• 2017

A comparative study of microwave and conventional sintering of lead-free $Bi_{1/2}(Na_{0.82}K_{0.18})_{1/2}TiO_3-BaZrO_3-CuO$ ceramics is presented. It was found that microwave sintering (MWS) can be successfully applied to the fabrication of large strain Bi-perovskite with electric field-induced strains comparable to those obtained with conventional sintering (CFS). Although MWS resulted in smaller grained microstructures than CFS, the ferroelectric properties were stronger in MWS-derived specimens than in the CFS-derived ones. The piezoelectric strain constant $d_{33}{^*}$ of the CFS-derived specimens reached a maximum value of 372 pm/V after sintering at $1100^{\circ}C$, whereas that of MWS-derived specimens peaked at $950^{\circ}C$ with a $d_{33}{^*}$ value of 324 pm/V.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.33.2-33.2
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• 2009

Dielectric and piezoelectric properties of Lead-free $(1-x)(Bi_{0.5}K_{0.5})TiO_3-xBiFeO_3$ceramics prepared by a conventional solid state reaction method were investigated in the range of x = 0~10 mol%. Piezoelectric coefficient was increased from 31 pC/N at x = 0 mol% to 64 pC/N at x = 6 mol% then decreased with increasing x. Electromechanical coupling factor ($K_p$) was increased up to 0.18 at x = 10 mol%. On the other hand, mechanical quality factor ($Q_m$) was decreased. Grain size was not much changed with various x and a single perovskite with tetragonal symmetry was maintained at all compositions forming a solid solution between $(Bi_{0.5}K_{0.5})TiO_3$ and $BiFeO_3$. Depolarization temperature ($T_d$) was gradually decreased with increasing x from $302^{\circ}C$ at x = 0 to $245^{\circ}C$ at x = 10 mol%.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.10
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• pp.1056-1060
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• 2004

In this study, 0.96B $i_{0.5}$($Na_{0.84}$ $K_{0.16}$)$_{0.5}$Ti $O_3$ + 0.04SrTi $O_3$ + 0.3 wt% N $b_2$ $O_{5}$+0.2 wt% L $a_2$ $O_3$ + xwt % Mn $O_2$ were investigated as a function of the amount of Mn $O_2$ addition in order to improve dielectric and piezoelectric properties of Lead-free piezoelectric ceramics. With increasing the amount of Mn $O_2$ addition, the density, electromechanical coupling factor( $k_{p}$), piezoelectric constant( $d_{33}$, $g_{33}$) and curie temperature (Tc) showed the maximum value of 5.7 g/㎤, 38 %, 219 pC/N, 26 mVㆍm/N and 32$0^{\circ}C$ at 0.1 wt% Mn $O_2$ addition, respectively, and mechanical quality factor( $Q_{m}$ ) showed the maximum value of 158 at 0.3 wt% Mn $O_2$ addition.ddition.ion.n.

• Korean Journal of Materials Research
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• v.15 no.10
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• pp.639-643
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• 2005

Lead-free $[Bi_{0.5}(Na_{1-x}K_x)_{0.5}TiO_3](x=0\~1.0)$ ceramics were prepared using a solid state reaction method and their structural and electrical characteristics were investigated. X-ray investigations indicated that the rhombohedral-tetragonal morphotropic phase boundary(MPB) of the $[Bi_{0.5}(Na_{1-x}K_x)TiO_3$ ceramics exists in the range of $x=0.16\~0.20$. The optimum values of piezoelectric constant$(d_{33})$, dielectric constant, and electromechanical coupling factor $(k_p)$ were obtained at $x=0.16\~0.20$ of the MPB region.