• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.6 no.2
• /
• pp.155-165
• /
• 1996

Growth of $LiNbO_3$ single crystal by Czochralski method was carried out to study the piezoelectric effects. Piezoelectric coefficients and elastic compliances of the $LiNbO_3$ single crystal were determined by the resonance method of length-extentional mode of bar resonator from the room temperature up to $100^{\circ}C$. Two dielectric constants of $LiNbO_3$ were also determined by measuring the capacitance of the plate specimen. Measured constants were piezoelectric coefficients $d_{15},d_{22},d_{31},d_{33}$ elastic compliances $s^E_{11},s^E_{33},2s^E_{13}+2s^E_{44},s^E_{14}$ and dielectric constants $K^T_{11},K^T_{33}$. As temperature increased, elastic compliances changed very slowly while piezoelectric coeffiecients and dielectric constant $K^T_{33}$ changed very rapidly. Electromechanical coupling constant of zyw ($45^{\circ}C$)-bar was as high as 0.51 in room temperature and nearly constant up to $1000^{\circ}C$. The increase of piezoelectric coefficients was mainly due to the increase of dielectric permittivity.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.51 no.11
• /
• pp.526-530
• /
• 2002

The $(Sr_{0.9}Ca_{0.1})TiO_3(SCT)$ thin films were deposited on Pt-coated electrode (Pt/TiN/$SiO_2$/Si) using RF sputtering method. The composition of SCT thin film deposited on Si substrate at room temperature is close to stoichiometry(1.081 in A/B ratio). The maximum dielectric constant of SCT thin film was obtained by ammealing at $600^{\cric}C$. The temperature dependence of dielectric loss showed a value within 0.02 in temperature ranges of -80 ${\sim}$ +90$^{\circ}C$. The capacitance characteristics showed a stable value within ${\pm}$4%. The drastic decrease of dielectric constant and increase of dielectric loss in SCT thin films was observed at the frequency above 200kHz.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2002.07a
• /
• pp.127-130
• /
• 2002

In this study, development of a new LTCC material using a non-glassy system was attempted with respect to reducing the fabrication process steps and cost down. Lowering the sintering temperature can be achieved by liquid phase sintering. For LTCC application, the starting material must have quality factor as high as possible in microwave frequency range. And also, the material should have a low dielectric constant for enhancing the signal propagation speed. Regarding these factors, dielectric constants of various materials were estimated by the Clausius-Mosotti equation. Among them, CaWO$_4$ was tamed out the suitable LTCC material. CaWO$_4$ can be sintered up to 98% of full density at 1200$^{\circ}C$ for 3 hours. It's measured dielectric constant, quality factor, and temperature coefficient of resonant frequency were 10.15, 62880GHz, and -27.8ppm/$^{\circ}C$, respectively. In order to modify the dielectric properties and densification temperature, 0.5∼1.5 wt% LiF were added to CaWO$_4$. LiF addition reduced the sintering temperature/time down to 800$^{\circ}C$/10∼30min due to the reactive liquid phase sintering. Dielectric constant lowered from 10.15 to 9.38 and Q x fo increased up to 92000GHz with increasing LiF content.

• Proceedings of the KIEE Conference
• /
• 1998.07d
• /
• pp.1456-1458
• /
• 1998

The $(Sr_{1-x}Ca_x)TiO_3(SCT)$ thin films were deposited at various substrate temperature using rf magnetron sputtering method on optimized Pt-coated electrodes ($Pt/TiN/SiO_2/Si$). The dielectric constant changes almost linearly in the temperature region of $-80{\sim}+90[^{\circ}C]$, the temperature characteristics of the dielectric loss exhibited a stable value within 0.1. The capacitance characteristics appears a stable value within ${\pm}5$[%]. The drastic decrease of dielectric constant and increase of dielectric loss in SCT thin films is observed above 200[kHz]. Dielectric constant of SCT thin films deposited on Si wafer substrate are larger with the increase of deposition temperature.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2001.11b
• /
• pp.430-433
• /
• 2001

The $0.96MgTiO_{3}-0.04SrTiO_{3}+xCe(x=0{\sim}1.6wt%)$ ceramics were fabricated by the conventional mixed oxide method. The sintering temperature and time were $1300^{\circ}C$, 2hr., respectively. From the X-ray diffraction patterns, it was found that the perovskite $SrTiO_{3}$ and ilmenite $MgTiO_{3}$ structures were coexisted in the $0.96MgTiO_{3}-0.04SrTiO_{3}+xCe(x=0{\sim}1.6wt%)$ ceramics. The dielectric constant$(\varepsilon_{r})$ was increased with addition of Ce. The temperature coefficient of resonant frequency$(\Gamma_{f})$ was gradually varied from positive value to the negative value with increasing the Ce. The temperature coefficient of resonant frequency of the $0.96MgTiO_{3}-0.04SrTiO_{3}+0.2Ce$ ceramics was near zero, where the dielectric constant, quality factor, and $\Gamma_{f}$ were 20.68, 50,272 and ${-0.5ppm/^{\circ}C}$, respectively.

• Journal of the Korean Chemical Society
• /
• v.6 no.1
• /
• pp.47-53
• /
• 1962

The "reactivity" of coal is one of the important characteristics of a coal used as a process raw material as well as a fuel. In this study, the reactivity was measured in terms of the magnitude of the reaction rate constant in the reduction of carbon dioxide with coal. A reactivity-testing apparatus was designed and constructed, and its performance characteristics were investigated by using Korean anthracite and hard-wood charcoal. Experiments were carried out at temperatures ranging from 750 to 1100$^{\circ}C$ with pulverized Korean anthracite whose sizes range from 1 to 10mm in diameter. Results showed that the reaction rate constant was not appreciably affected by the particle size investigated, and the reactivities of the anthracite and the charcoal were found to be a function of reaction temperature alone. It was also found that a straight line was produced when the logarithm of the rate constant is plotted against the reciprocal of the absolute temperature. The reactivities of the charcoal were found to be 2 to 10 times higher than those of the anthracite at a temperature ranging from 750 to 1100$^{\circ}C$, and 90% of carbon dioxide was reduced to carbon monoxide by the anthracite at a temperature above 1050$^{\circ}C$.

• Proceedings of the KIEE Conference
• /
• 2006.10a
• /
• pp.20-21
• /
• 2006

In this study, structural and microwave dielectric properties of the ${Ba_5}{B_4}{O_{15}}$ (B=Ta, Nb} cation-deficient perovskite ceramics with sintering temperature were investigated. All sample of the ${Ba_5}{B_4}{O_{15}}$ (B=Ta, Nb) ceramics prepared by conventional mixed oxide method and sintered at $1325^{\circ}C{\sim}1575^{\circ}C$. The bulk density and dielectric constant of the ${Ba_5}{Ta_4}{O_{15}}$ ceramics were increased continuously with increasing of sintering temperature. And the bulk density and dielectric constant of the ${Ba_5}{Nb_4}{O_{15}}$ ceramics was increased in $1375^{\circ}C{\sim}1400^{\circ}C$ but decerased in $1425^{\circ}C$. In the case of ${Ba_5}{Ta_4}{O_{15}}$ ceramics sintered at $1475^{\circ}C$ and ${Ba_5}{Nb_4}{O_{15}}$ ceramics sintered at $1400^{\circ}C$, The dielectric constant and 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.

• Bulletin of the Korean Chemical Society
• /
• v.34 no.8
• /
• pp.2473-2479
• /
• 2013

The kinetics of the radical-polar molecule reaction $CH_3+HBr{\rightarrow}CH_4+Br$ has been studied at temperatures between 150 and 1000 K using classical dynamics procedures. Potential energy surfaces constructed using analytical forms of inter- and intramolecular interaction energies show a shallow well and barrier in the entrance channel, which affect the collision dynamics at low temperatures. Different collision models are used to distinguish the reaction occurring at low- and high-temperature regions. The reaction proceeds rapidly via a complex-mode mechanism below room temperature showing strong negative temperature dependence, where the effects of molecular attraction, H-atom tunneling and recrossing of collision complexes are found to be important. The temperature dependence of the rate constant between 400 and 1000 K is positive, the values increasing in accordance with the increase of the mean speed of collision. The rate constant varies from $7.6{\times}10^{-12}$ at 150 K to $3.7{\times}10^{-12}$ at 1000 K via a minimum value of $2.5{\times}10^{-12}\;cm^3\;molecule^{-1}\;s^{-1}$ at 400 K.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.49 no.11
• /
• pp.603-608
• /
• 2000

$(Ba, Sr)TiO_{3}$[BST] thin films were fabricated on the Pt/TiO$_2$/SiO$_2$/Si substrate by the RF sputtering. The structure and dielectric properties of the BST thin films with the substrate temperature were investigated. Increasing the substrate temperature, The BST phase increased and barium multi titanate phases decreased. Increasing the frequency, the dielectric constant decreased and the dielectric loss increased. The dielectric constant and dielectric loss of the BST thin films deposited at 50$0^{\circ}C$ were 300 and 0.018, respectively at 1 kHz. The leakage current density of the BST thin films deposited at 50$0^{\circ}C$ was $10^{-9}$ A/$\textrm{cm}^2$ with applied voltage of 3V. Because of the high dielectric constant(300), low dielectric loss(0.018) and low leakage current($10^{-9}$ A/$\textrm{cm}^2$), BST thin films deposited at 50$0^{\circ}C$ is expecting for the application of DRAM.

• Electrical & Electronic Materials
• /
• v.10 no.6
• /
• pp.533-540
• /
• 1997

The microwave dielectric properties of ((P $b_{1-x}$ C $a_{x}$)Zr $O_3$ and (P $b_{0.63}$,C $a_{0.37-x}$ $M_{x}$)Zr $O_3$(M=Mg,Sr) ceramics were investigated. In (P $b_{1-x}$ C $a_{x}$)Zr $O_3$ (X=0.33~0.40) ceramics, high quality factor and small temperature coefficient of resonant frequency were obtain in (P $b_{0.63}$C $a_{0.37}$)Zr $O_3$with perovskite structure. In the case of (P $b_{0.63}$C $a_{0.37-x}$M $g_{x}$)Zr $O_3$ dielectric constant temperature coefficient of resonant frequency increased and quality factor decreased due to increase of polarization of A-O bonding. When replacing Ca ion with Sr ion with large ion radius, polarization decreased with increased of bonding length and thus dielectric constant and temperature coefficient of resonant frequency decreased.decreased.creased.