• Korean Journal of Materials Research
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• v.12 no.6
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• pp.464-469
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• 2002

$SrBi_2Nb_2O_9(SBN)$ thin films were grown on Pt/Ti/Si and p-type Si(100) substrates by rf-magnetron co-sputtering method using two ceramic targets, $SrNb_2O_6\; and \;Bi_2O_3$. The structural and electrical characteristics have been investigated to confirm the possibility of the SBN thin films for the applications to destructive and nondestructive read out ferroelectric random access memory(FRAM). For the optimum growth condition X-ray diffraction patterns showed that SBN films had well crystallized Bi-layered perovskite structure after $700^{\circ}C$ heat-treatment in furnace. From this specimen we got remnant polarization $(2P_r)$ of about 6 uC/$\textrm{cm}^2$ and coercive voltage $(V_c)$ of about 1.5 V at an applied voltage of 5 V. The leakage current density was $7.6{\times}10^{-7}$/A/$\textrm{cm}^2$ at an applied voltage of 5V. And for the NDRO-FRAM application, properties of SBN films on Si substrate has been investigated. From transmission electron microscopy (TEM) analysis, we found the furnace treated sample had a native oxide about 2 times thicker than the RTA treated sample and this thick native oxide layer had a bad effect on C-V characteristics of SBN/Si thin film. After $650^{\circ}C$ RTA process, we got the improved memory window of 1.3 V at an applied voltage of 5 V.

• Journal of the Korean Magnetics Society
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• v.11 no.2
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• pp.45-49
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• 2001

Effects of multilayer structure and annealing condition on the soft magnetic properties of sputtered Fe/CoNbZr multilayers were investigated. We observed a minimum coercivity (1.1 Oe) at 5 nm thick Fe layer and the maximum permeability (2300) at 15 nm Fe layer and high saturation magnetization in the as-deposited state. As a result of increase of Fe grain size, coercivity increases with increasing Fe layer thickness. Degradation of ${\mu}$ at the thin Fe layer region may be due to the intermixed phase of high magnetostriction, such as CoFe. Optimum annealing condition was obtained through annealing at 300 $^{\circ}C$ for 40 min (${\mu}$=2500, H$\sub$c/=0.35 Oe). Enhancement of permeability was observed in the temperature range of 250∼300$^{\circ}C$. These results may closely be related with lowering the anisotropy energy by lattice deformation (0.4%) and enhanced uniaxial anisotropy.

• Electrical & Electronic Materials
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• v.9 no.10
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• pp.991-1000
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• 1996

PbTiO$_{3}$-PbZrO$_{3}$-Pb(Ni$_{1}$3/Nb$_{2}$3/O$_{3}$) (PZT-PNN) thin films were prepared from corresponding metal organics partially stabilized with diethanolamine by the sol-gel spin coating method. Each mol ratio of PT:PZ:PNN solutions were #1(50:40:10), #2(50:30:20), #3(45:35:20), #4(40:40:20), #5(40:50:10), #6(35:45:20) and #7(30:50:20) respectively. The spin-coated PZT-PNN films were heat-treated at 350.deg. C for decomposition of residual organics, and were sintered from 450.deg. C to 750.deg. C for crystallization. The substrates, such as Pt and Pt/TiN/Ti/TiN/Si were used for the spin coating of PZT PNN films. The perovskite phase was observed in the PZT-PNN films heat-treated at 500.deg. C. The crystalline of the PZT-PNN films was optimized at the sintering of 700.deg. C. By the result of AES analysis, It is confirmed that the films of TiN/Ti/TiN was a good diffusion barrier and that co-diffusion into the each films was not observed.

• Electrical & Electronic Materials
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• v.10 no.2
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• pp.134-140
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• 1997

PbTiO$_{3}$-PbZrO$_{3}$-Pb(Ni$_{1}$3/Nb $_{2}$3/O$_{3}$)(PZT-PNN) thin films were prepared from corresponding metal organics partially stabilized with diethanolamine by the sol-gel spin coating method. Each mol rates of PT:PZ:PNN solutions were #1(50:40:10), #2(50:30:20), #3(45:35:20) and #4(40:40:20), respectively. The spin-coated PZT-PNN films were sintered at the temperature from 500.deg. C to 600.deg. C for crystallization. The P-E hysteresis curve was drawn by Sawyer-Tower circuit with PZT-PNN film. The coercive field and the remanent polarization of #4(40:40:20 mol%) PZT-PNN film were 28.8 kV/cm and 18.3 .mu.C/cm$^{2}$, respectively. Their dielectric constants were shown between 128 and 1120, and became maximum value in MPB(40:40:20 mol%). The leakage currents of PZT-PNN films were about 9.4x 10$^{-8}$ A/cm$^{2}$, and the breakdown voltages were about 0.14 and 1.1 MV/cm. The Curie point of #3(45:35:20 mol%, sintered at 600.deg. C) film was 330.deg. C.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2004.06a
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• pp.355-355
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• 2004

사용후핵연료 금속전환체는 세라믹형 사용후핵연료를 리튬용융염으로 금속전환하여 생성한 우라늄금속으로 상온에서도 표면산화가 진행될 정도로 매우 불안정한 상태이다. 이에 대한 저장 안정성 향상방안을 도출하기 위해 금속전환체의 주성분인 금속우라늄과 산화 안정화물질인 Nb을 첨가한 모의 금속전환체 합금을 제작하여 $200^{\circ}C~300^{\circ}C$ 온도구간에서 열중량분석기(TGA)를 이용해 순수 산소분위기로 산화시험을 수행하였다.(중략)

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.8
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• pp.617-621
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• 2010

($K_{0.5}Na_{0.5}$)($Nb_{0.96}Sb_{0.04}$)$O_3$+1.2 mol% $K_4CuNb_8O_{23}$ ceramics doped with iron oxide ($Fe_2O_3$) were prepared by a conventional mixed oxide method. And then, their piezoelectric and dielectric properties were investigated as a function of $Fe_2O_3$ addition. X-ray diffraction studies reveal that $Fe^{3+}$ diffuses into the NKN lattices to form a solid solution with a pure perovskite structure at room temperature. At the sintering temperature of $1,060^{\circ}C$, when 0.2 mol% $Fe_2O_3$ was doped, the piezoelectric constant ($d_{33}$), electromechanical coupling factor (Kp), and mechanical quality factor ($Q_m$) showed the excellent values of 131.67 pC/N, 0.436, and 696.36, respectively. Results show that $Fe_2O_3$ deped ($K_{0.5}Na_{0.5}$)($Nb_{0.96}Sb_{0.04}$)$O_3$+1.2 mol% $K_4CuNb_8O_{23}$ lead-free piezoelectric ceramics are a promising lead free material for piezoelectric transformer applications.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.3
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• pp.289-293
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• 2004

PNW-PMN-PZT ceramics were fabricated with the variations of Nb$_2$O$_{5}$ addition and their microstructural and piezoelectric characteristics were investigated. When the amount of Nb$_2$O$_{5}$ increased, grain size decreased gradually. At 0.3wt％ Nb$_2$O$_{5}$ which is the same weight percent with Fe$_2$O$_3$, maximum tetragonality(c/a) and density were shown due to the complexed doping effects. Also, this composition that showed Qm of 2,041, kp of 0.55, grain size of 2.5${\mu}{\textrm}{m}$ and $\varepsilon$r of 1704 were proper for high power application. Using this composition, Rosen-type piezoelectric transformer was fabricated as the size of 1 ${\times}$ 16 ${\times}$ 5㎣ and its electrical characteristics were investigated with the variations of load resistance and driving frequency. At the resistance of 200㏀, maximum step-up ratio of 13.68 was shown. After driving PDA CCFL for 25 min using the inverter circuit, at driving frequency of 214.4KHz, input voltage of 31.78 V and input current of 21.1mA were measured at the input part of piezoelectric transformer. And then, output voltage of 293.2 V and output current of 2.2mA were shown at the output part of piezoelectric transformer. At the same time, efficiency of 96.2％ and temperature rise of 3.5$^{\circ}C$ were appeared at the piezoelectric transformer.ormer.

• Korean Journal of Materials Research
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• v.15 no.2
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• pp.89-92
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• 2005

The induction melting was employed to prepare Nb-doped $CoSb_3$ skutterudites and their thermoelectric properties were investigated. Single phase $\delta-CoSb_3$ was successfully obtained by induction melting and subsequent annealing at $400^{\circ}C$ for 2 hrs in vacuum. The positive signs of Seebeck coefficients for all the specimens revealed that Nb atoms acted as p-type dopants by substituting Co atoms. Electrical conductivity decreased and then increased with increasing temperature, indicating mixed conduction behavior. Electrical conductivity increased by Nb doping, and it was saturated at high temperature. Maximum value of the thermoelectric power factor was shifted to higher temperature with increasing the amount of Nb doping, mainly originated from the high Seebeck coefficient around mixed conduction temperature and high electrical conductivity.

• Current Applied Physics
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• v.18 no.12
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• pp.1523-1527
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• 2018

The thermal stability, magnetic and magnetocaloric properties of $Gd_{55}Co_{35}M_{10}$ (M = Si, Zr and Nb) melts-pun ribbons were studied. The relatively high reduced glass transition temperature ($T_{x1}/T_m$ > 0.60) and low melting point ($T_m$) resulted in excellent glass forming ability (GFA). The Curie temperatures ($T_C$) of melt-spun amorphous ribbons $Gd_{55}Co_{35}M_{10}$ for M = Si, Zr and Nb were 166, 148 and 173 K, respectively. For a magnetic field change of 2 T, the values of maximum magnetic entropy change $(-{\Delta}S_M)^{max}$ for $Gd_{55}Co_{35}Si_{10}$, $Gd_{55}Co_{35}Zr_{10}$ and $Gd_{55}Co_{35}Nb_{10}$ were found to be 2.86, 4.28 and $4.05J\;kg^{-1}K^{-1}$, while the refrigeration capacity (RC) values were 154, 274 and $174J\;kg^{-1}$, respectively. The $RC_{FWHM}$ values of amorphous alloys $Gd_{55}Co_{35}M_{10}$ (M = Si, Zr and Nb) are comparable to or larger than that of $LaFe_{11.6}Si_{1.4}$ crystalline alloy. Large values of $(-{\Delta}S_M)^{max}$ and RC along with good thermal stability make $Gd_{55}Co_{35}M_{10}$ (M = Si, Zr and Nb) amorphous alloys be potential materials for magnetic cooling operating in a wide temperature range from 150 to 175 K, e.g., as part of a gas liquefaction process.

• Korean Journal of Optics and Photonics
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• v.7 no.1
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• pp.77-86
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• 1996

We employ the SOR method to analyze CPW electrodes of Ti:$LiNbO_3$ Mach-Zehnder traveling-wave optical modulator in the tapered region of an optical modulator. In the tapered region of the modulator, we design the electrodes satisfying $Z_c=50{\Omega}$. In the modulation region, we find two find sets of design parameters. One set is for $Z_c=50{\Omega}$, $n_{eff}=2.26$ and the another is for $n_{eff}=2.2$, $Z_c=47.7{\Omega}$.