• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.3
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• pp.198-203
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• 2012

In this study, $[Li_{0.04}(Na_{0.5}K_{0.5})_{0.96}](Nb_{0.86}Ta_{0.10}Sb_{0.04})O_3+xSrO$ (x=0, 0.0025, 0.005, 0.0075) ceramics were synthesized by the conventional mixed oxide method. The X-ray diffraction patterns demonstrated that ceramics possessed single perovskite structure. The SEM images indicate that microstructure can be obviously affected by a small amount of added SrO. The phase transition temperature tetragonal-cubic($T_c$) and orthorhombic-tetragonal($T_{o-t}$) shifts downward and upward with the increase of Sr addition, respectively. The excellent piezoelectric properties of $d_{33}=170[pC/N]$, $k_p=0.37$, $Q_m=64.12$, $T_{o-t}=153^{\circ}C$ and $T_c=370^{\circ}C$ were obtained from the 0.25 mol% Sr added ceramics sintered at $1,120^{\circ}C$ for 1 h.

• Proceedings of the KIEE Conference
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• 2003.10a
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• pp.98-100
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• 2003

The microwave dielectric properties and microstructure of the $0.7Mg_4Ta_2O_9-0.3CaTiO_3$ ceramics were investigated. All sample of the $0.7Mg_4Ta_2O_9-0.3CaTiO_3$ ceramics were prepared by conventional mixed oxide method. The sintering temperature was $1375^{\circ}C{\sim}1450^{\circ}C$. The structural properties of the $0.7Mg_4Ta_2O_9-0.3CaTiO_3$ ceramics were investigated by X-ray diffractormeter. According to the X-ray diffraction patterns of the $0.7Mg_4Ta_2O_9-0.3CaTiO_3$ ceramics, the major phase of the hexagonal $Mg_4Ta_2O_9$ were presented. In the case of the $0.7Mg_4Ta_2O_9-0.3CaTiO_3$ ceramics sintered at $1425^{\circ}C$, density, dielectric constant, quality factor were $5.799g/cm^2$, 23.26, 40,054 GHz, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.682-685
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• 2002

The $0.96MgTiO_3-0.04SrTiO_3$ ceramics with $B_2O_3$(10wt%) were prepared by the conventional mixed oxide method. The structural properties were investigated with sintering temperature by XRD. According to the X-ray diffraction pattern of the $0.96MgTiO_3-0.04SrTiO_3$ ceramics with $B_2O_3$(10wt%), the ilmenite $MgTiO_3$ and perovskite $SrTiO_3$ structures were coexisted and secondary phase of the $MgTi_2O_5$ were appeared. In the case of $0.96MgTiO_3-0.04SrTiO_3+B_2O_3$(10wt%) ceramics sintered $1225^{\circ}C$, dielectric constant, quality factor and temperature coefficient of resonant frequency were 19.82, 62,735GHz, $-2.983ppm/^{\circ}C$, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.363-366
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• 2004

The structural and microwave dielectric properties of $0.7Mg_4Ta_2O_9-0.3SrTiO_3$ ceramics with sintering temperature were investigated. All the sample of the $0.7Mg_4Ta_2O_9-0.3SrTiO_3$ ceramics were prepared by conventional mixed oxide method and sintered at $1425^{\circ}C{\sim}1500^{\circ}C$. According to XRD Patterns, hexagonal $Mg_4Ta_2O_9$ phase and cubic $SrTiO_3$ Phase were coexisted. The porosity of $0.7Mg_4Ta_2O_9-0.3SrTiO_3$ ceramics were reduced with increasing sintering temperature. In the case of $0.7Mg_4Ta_2O_9-0.3SrTiO_3$ ceramics sintered at $1475^{\circ}C$, dielectric constant, quality factor and temperature coefficient of resonant frequency were 14.51, 82,596GHz and $-3.14ppm/^{\circ}C$, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.8
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• pp.840-845
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• 2004

The microstructure and microwave dielectric properties of $(1-x){Mg}_4{Ta}_2{O}_9-xTi{O}_2(x=0\sim0.9)$ ceramics were investigated. The specimens were prepared by the conventional mixed oxide method with sintering temperature of 140$0^{\circ}C$∼150$0^{\circ}C$. To improve the quality factor and the temperature coefficient of resonant frequency,$ Ti{O}_2(\varepsilon\Gamma=100, Q\times f_\Gamma=40,000 GHz,\ta_f= +450 ppm\diagup^{\circ}C $ was added in ${Mg}_4{Ta}_2{O}_9$ceramics. The dielectric and structural properties were investigated. According to the XRD patterns, $(1-x){Mg}_4{Ta}_2{O}_9-xTi{O}_2(x=0\sim0.9)$ ceramics had the ${Mg}_4{Ta}_2{O}_9$ phase(hexagonal) and ${MgTi}_2{O}_5$phase(orthorhombic). The dielectric constant($\varepsilon_r$). quality($Qtimes{f}_r$${\tau}_f$) of the $(1-x){Mg}_4{Ta}_2{O}_9-xTi{O}_2(x=0\sim0.9)$ ceramics were 8.12∼18.59, 18,750∼186,410 GHz and －36.02∼＋3.46 ppm/$^{\circ}C$, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.7
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• pp.506-510
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• 2012

In this study, lead-free $(Na_{0.465}K_{0.465}Bi_{0.07})(Nb_{0.93}Ti_{0.07})O_3-0.08MnO_2$ ceramics were fabricated by conventional mixed oxide method. Structural and electrical properties of lead-free $(Na_{0.465}K_{0.465}Bi_{0.07})(Nb_{0.93}Ti_{0.07})O_3-0.08MnO_2$ ceramics with the variation of sintering temperature were investigated. As results of x-ray diffraction analysis, all specimens showed a typical polycrystalline perovskite structure without presence of the second phase. Sintered density increased with an increases of sintering temperature and the specimen sintered at $1,020^{\circ}C$ showed the maximum value of 4.5 $g/cm^3$. The average grain size of the $(Na_{0.465}K_{0.465}Bi_{0.07})(Nb_{0.93}Ti_{0.07})O_3-0.08MnO_2$ specimen sintered at $1,020^{\circ}C$ is about 0.83 ${\mu}m$. Electromechanical coupling factor, relative dielectric constant and dielectric loss of $(Na_{0.465}K_{0.465}Bi_{0.07})(Nb_{0.93}Ti_{0.07})O_3-0.08MnO_2$ specimens sintered at $1,020^{\circ}C$ were 0.252, 741 and 0.043% respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.2
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• pp.104-108
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• 2013

In this paper, the $0.95(Na_{0.5}K_{0.5})_{0.04}[(Nb_{0.8}Ta_{0.20})_{0.994}Co_{0.015}]O_3$(abbreviated as NKNT) + $0.05KNbO_3$ lead-free piezoelectric ceramics were synthesized by the conventional mixed oxide method route with normal sintering. And also, the effects of calcination temperature on the microstructure, dielectric properties, and piezoelectric properties were investigated. A polymorphic phase transition(PPT) between orthorhombic and tetragonal phases was observed in specimens calcined at $810^{\circ}C{\sim}850^{\circ}C$. The ceramics calcined at $830^{\circ}C$ showed excellent piezoelectric properties: $d_{33}$= 179 pC/N, $k_p$= 0.384, $Q_m$= 79.73). These results indicate that the ceramic is a promising candidate material for lead-free piezoelectric ceramics.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.1
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• pp.29-32
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• 2012

Lead-free $0.98(Na_{0.5},K_{0.5})NbO_3-0.02Li(Sb_{0.17}Ti_{0.83})O_3$ (hereafter 0.98NKN-0.02LST) ceramics doped with $Ag_2O$ were prepared using a conventional mixed oxide method. The specimen showed superior structural and electrical properties when 1 mol% $Ag_2O$ was doped. For the 0.98NKN-0.02LST+1.0mol%$Ag_2O$ ceramics sintered at $1,100^{\circ}C$, piezoelectric constant ($d_{33}$) of sample showed the optimum values of 207 pC/N. The 0.98NKN-0.02LST+1.0 mol%$Ag_2O$ ceramics are a promising candidate for lead-free piezoelectric materials.

• 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.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.7
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• pp.1208-1212
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• 2008

In this study, both structural and microwave dielectric properties of the $Ba_5B_4O_{15}$ (B=Ta, Nb) cation-deficient perovskite ceramics with sintering temperature were investigated. All samples of the $Ba_5B_4O_{15}$ (B=Ta, Nb) ceramics were prepared by the conventional mixed oxide method and sintered at $1325^{\circ}C{\sim}1575^{\circ}C$. The bulk density and dielectric constant of the $Ba_5Ta_4O_{15}$ ceramics were increased continuously with increasing of sintering temperature. The quality factor of the $Ba_5Ta_4O_{15}$ ceramics was increased in as the sintering temperature increases from $1375^{\circ}C{\sim}1475^{\circ}C$ but decreased at the temperatures above $1475^{\circ}C$. And the bulk density, dielectric constant and quality factor of the $Ba_5Nb_4O_{15}$ ceramics were increased in as the sintering temperature increases from $1325^{\circ}CP{\sim}1400^{\circ}C$ but decreased at the temperatures above $1400^{\circ}C$. In the case of the $Ba_5Ta_4O_{15}$ sintered at $1475^{\circ}C$ and $Ba_5Nb_4O_{15}$ ceramics sintered at $1400^{\circ}C$, the dielectric constant, quality factor, and temperature coefficient of the resonant frequency (TCRF) were 25.15, 53,105 GHz, -3.06 $ppm/^{\circ}C$ and 39.55, 28,052 GHz, +5.7 ppm/$^{\circ}C$, respectively.