• Korean Journal of Materials Research
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• v.14 no.9
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• pp.627-633
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• 2004

Lithium titanate whiske($Li_{x}Ti_{4}O_9$) was prepared by an ion-exchange reaction. To this end, the initial material, potassium tetratitanate ($K_{2}Ti_{4}O_9{\cdot}nH_{2}O$) was prepared by calcination of a mixture of $K_{2}CO_3\;and\;TiO_2$ with a molar ratio of 2.8 at $1050^{\circ}C$ for 3 h, followed by boiling water treatment of the calcined products for 10 h. Fibrous potassium tetratitanate could be transformed into layered hydrous titanium dioxide ($H_{2}Ti_{4}O_9{\cdot}nH_{2}O$) through an exchange of $K^{+}\;with\;H^{+}$ using 0.075 M HCl. Also, lithium titanate whisker was finally prepared as $Li^{+}\;and\;H^{+}$ ions were exchanged by adding 20 mL of a mixture solution of LiOH and $LiNO_3$ to 1g whisker and stirring for $5\~15$ days. The average length and diameter of the $Li_{x}Ti_{4}O_9$ whiskers were $10\~20{\mu}m\;and\;1\~3{\mu}m$, 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.513-519
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• 2023

It was reported that a tetragonal phase can be stabilized with maintaining good piezoelectric properties when Na_0.5K_0.5NbO₃ (KNN) is modified with 0.06 mol SrTiO₃. However, such a high amount of SrTiO₃ leads not only to poor sinterability but low Curie temperature (T_C). To maintain high TC with good piezoelectric properties in KNN-based lead-free piezoelectric ceramics, this study investigates the effect of Li-doping on the dielectric and piezoelectric properties of 0.96Na_0.5K_0.5NbO₃-0.04SrTiO₃ (KNN-4ST) ceramics. As a result, the orthorhombic-tetragonal phase transition was observed at 2 mol% Li₂CO₃ modified KNN-4ST ceramics, whose T_C, d₃₃ and k_p values are 328℃, 165pC/N and 0.33, respectively.

• Proceedings of the Materials Research Society of Korea Conference
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• 1997.05a
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• pp.90-90
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• 1997

• Korean Journal of Materials Research
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• v.17 no.8
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• pp.447-451
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• 2007

We investigated the dependence of the various annealing conditions and thickness ($6\sim45nm$) of the Ti-doped $Al_2O_3$ coating on the electrochemical properties and the capacity fading of Ti-doped $Al_2O_3$ coated $LiCoO_2$ films. The Ti-doped-$Al_2O_3$-coating layer and the cathode films were deposited on $Al_2O_3$ plate substrates by RF-magnetron sputter. Microstructural and electrochemical properties of Ti-doped-$Al_2O_3$-coated $LiCoO_2$ films were investigated by transmission electron microscopy (TEM) and a dc four-point probe method, respectively. The cycling performance of Ti-doped $Al_2O_3$ coated $LiCoO_2$ film was improved at higher cut-off voltage. But it has different electrochemical properties with various annealing conditions. They were related on the microstructure, surface morphology and the interface condition. Suppression of Li-ion migration is dominant at the coating thickness >24.nm during charge/discharge processes. It is due to the electrochemically passive nature of the Ti-doped $Al_2O_3$ films. The sample be made up of Ti-doped $Al_2O_3$ coated on annealed $LiCoO_2$ film with additional annealing at $400^{\circ}C$ had good adhesion between coating layer and cathode films. This sample showed the best capacity retention of $\sim92%$ with a charge cut off of 4.5 V after 50 cycles. The Ti-doped $Al_2O_3$ film was an amorphous phase and it has a higher electrical conductivity than that of the $Al_2O_3$ film. Therefore, the Ti-doped $Al_2O_3$ coated improved the cycle performance and the capacity retention at high voltage (4.5 V) of $LiCoO_2$ films.

• Korean Journal of Materials Research
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• v.25 no.8
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• pp.423-428
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• 2015

Impedancemetric $NO_x$ (NO and $NO_2$) gas sensors were designed with a stacked-layer structure and fabricated using $LaCr_xCo_{1-x}O_3$ (x = 0, 0.2, 0.5, 0.8 and 1) as the receptor material and $Li_{1.3}Al_{0.3}Ti_{1.7}(PO_4)_3$ plates as the solid-electrolyte transducer material. The $LaCr_xCo_{1-x}O_3$ layers were prepared with a polymeric precursor method that used ethylene glycol as the solvent, acetyl acetone as the chelating agent, and polyvinylpyrrolidone as the polymer additive. The effects of the Co concentration on the structural, morphological, and $NO_x$ sensing properties of the $LaCr_xCo_{1-x}O_3$ powders were investigated with powder X-ray diffraction, field emission scanning electron microscopy, and its response to 20~250 ppm of $NO_x$ at $400^{\circ}C$ (for 1 kHz and 0.5 V), respectively. When the as-prepared precursors were calcined at $700^{\circ}C$, only a single phase was detected, which corresponded to a perovskite-type structure. The XRD results showed that as the Co concentration of the $LaCr_xCo_{1-x}O_3$powders increased, the crystal structure was transformed from an orthorhombic phase to a rhombohedral phase. Moreover, the $LaCr_xCo_{1-x}O_3$ powders with $0{\leq}x<0.8$ had a rhombohedral symmetry. The size of the particles in the $LaCr_xCo_{1-x}O_3$powders increased from 0.1 to $0.5{\mu}m$ as the Co concentration increased. The sensing performance of the stack-structured $LaCr_xCo_{1-x}O_3/Li_{1.3}Al_{0.3}Ti_{1.7}(PO_4)_3$ sensors was found to divide the impedance component between the resistance and capacitance. The response of these sensors to NO gas was more sensitive than that to $NO_2$ gas. Compared to other impedancemetric sensors, the $LaCr_{0.8}Co_{0.2}O_3/Li_{1.3}Al_{0.3}Ti_{1.7}(PO_4)_3$ sensor exhibited good reversibility and reliable sensingresponse properties for $NO_x$ gases.

• Journal of the Korean Ceramic Society
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• v.31 no.11
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• pp.1337-1345
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• 1994

Glasses in the system of 45CaO-25TiO2-30P2O5 containing 1 mole% of M2O(M=Li, Na, K) were melted and crystallized. And their crystal phases were Ca3(PO4)2, CaTi4(PO4)6, and TiO2. Porous glass-ceramics with skeleton of two crystal phase CaTi4(PO4)6 and TiO2 were prepared by selective leaching of Ca3(PO4)2 with 0.1 N-HCl. Glass transition temperature(Tg) and crystallization temperature(Tc) were decreased by addition of 1 mole% alkali metal oxide. Pore size of porous glass-ceramics was increased with increasing heat treatment temperature and its dependence on heat treatment temperature was decreased with addition of Na2O and K2O. It was found that porous glass-ceramics of parent glass and containing 1mole% M2O(M=Li, Na, K) composition had maximum specific surface area, porosity and maximum of crystallzed phase by heat treatment at 80$0^{\circ}C$, 76$0^{\circ}C$, 78$0^{\circ}C$, 80$0^{\circ}C$ respectively.

• Korean Journal of Materials Research
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• v.11 no.5
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• pp.339-344
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• 2001

An all solid-state thin film supercapacitor (TFSC) with Co$_3$O$_4$/LiPON/Co$_3$O$_4$ structure was fabricated on Pt/Ti/Si substrate using Co$_3$O$_4$ thin film electrode. Each Co$_3$O$_4$ film was grown by reactive dc reactive magnetron sputtering with increasing $O_2$/[Ar+O$_2$] ratio. Amorphous LiPON electrolyte film was deposited on Co$_3$O$_4$/Pt/Ti/Si in pure nitrogen ambient by using reactive rf magnetron sputtering. The electrochemical behavior of the Co$_3$O$_4$/LiPON/Co$_3$O$_4$ multi-layer structures exhibits a behavior of a bulk-type supercapacitor, even though much lower capacity (from 5 to 25 mF/$\textrm{cm}^2$-$\mu\textrm{m}$) than that of the bulk one. It was found that the TFSC showed a fairly constant discharge capacity with a constant current of 50 $\mu\textrm{A}/\textrm{cm}^2$ at the cut-off voltage 0-2V during 400 cycles. It is shown that the electrochemical behavior of the Co$_3$O$_4$/LiPON/Co$_3$O$_4$ TFSC is dependent upon the sputtering gas ratio. The capacity dependency of electrode films on different gas ratios was explained by different structural, electrical, and surfacical properties.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.297-297
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• 2007

The $(B_{0.5},Sr_{0.5})TiO_3$ ceramics, which added with low sintering materials $Li_2CO_3$ and ZnBO, was investigated for LTCC(low temperature co-fired ceramic) applications. To compare sintering temperature of $(B_{0.5},Sr_{0.5})TiO_3$ respectively, we added 1, 2, 3, 4, and 5wt% of $Li_2CO_3$ and ZnBO to $(B_{0.5},Sr_{0.5})TiO_3$. For confirming the sintering temperature, the respective specimens were sintered from $750^{\circ}C$ to $1200^{\circ}C$ by $50^{\circ}C$. The case of $Li_2CO_3$ greatly lowered the sintering temperature of $(B_{0.5},Sr_{0.5})TiO_3$ ($1350^{\circ}C$) below $900^{\circ}C$. The addition of ZnBO improved the loss tangent of $(B_{0.5},Sr_{0.5})TiO_3$. The crystalline structure of $LiCO_3$ doped $(B_{0.5},Sr_{0.5})TiO_3$ and ZnBO doped $(B_{0.5},Sr_{0.5})TiO_3$ was analyzed with the X-ray diffraction (XRD) analysis. The dielectric permittivity and loss tangent of $Li_2CO_3$ doped BST and ZnBO doped BST were measured with the HP 4284A precision. From the electrical characterization, we respectively obtained the dielectric permittivity 1361, loss tangent $6.94{\times}10^{-3}$ at $Li_2CO_3$ doped $(B_{0.5},Sr_{0.5})TiO_3$ (3wt%) and the dielectric constant 1180, loss tangent $3.70{\times}10^{-3}$ at ZnBO doped $(B_{0.5},Sr_{0.5})TiO_3$(5wt%).

• Journal of the Korean Ceramic Society
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• v.40 no.4
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• pp.328-332
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• 2003

Ceramics of xCaTiO$_3$-(1-x)Li$_{0.5}$Nd$_{0.5}$TiO$_3$(xCT-(1-x)LNT) series have been prepared by the mixed oxide route. Powders were calcined at 110$0^{\circ}C$ ; cylindrical specimens were fired at temperatures in the range 1300-150$0^{\circ}C$. Sintered products were typically 90-95% dense. The microstructures were dominated by angular grains typically 1.3${\mu}{\textrm}{m}$ to 3.5 ${\mu}{\textrm}{m}$ in size. Twinning in the microstructures was analysed using Electron Back Scattered Diffraction (EBSD). Microwave dielectric properties of xCT-(1-x)LNT at 2.1 GHz ($\varepsilon$$_{r}$, Qxf, and $\tau$r) were 170,3800 GHz and 744 ppm/$^{\circ}C$ for pure CaTiO$_3$ and 80,2000 GHz and -240 ppm/$^{\circ}C$ for LNT. The $\tau$r decreases almost linearly from 744 for pure CaTiO$_3$ to -240 for pure LNT.LNT.T.

• Proceedings of the KIEE Conference
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• 2006.10a
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• pp.3-4
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• 2006

${Li_2}{CO_3}$ and MgO doped paraelectric ${Ba_{0.5}}{Sr_{0.5}}{TiO_3}$, materials were prepared and compared for LTCC applications. In these days LTCC (Low Temperature Co-fired Ceramics) technology has been widely employed for electronic modules for the communication systems such as front-end modules, antenna modules, and switching modules. In this paper, 1 ${\sim}$ 5 wt % of ${Li_2}{CO_3}$, and 30 wt % of MgO were added to ${Ba_{0.5}}{Sr_{0.5}}{TiO_3}$, respectively. The crystalline properties and electrical properties will be compared and discussed.