• 한국전기전자재료학회논문지
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• 제27권1호
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• pp.14-17
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• 2014

In this study, lead-free Piezoelectric $(Na_{0.47}K_{0.47}Sr_{0.03}Ca_{0.03})(Nb_{0.94}Ti_{0.06})O_3$-0.1 $MnO_2$ ceramics were fabricated using mixed oxide method and the effects of various sintering temperature on the structural and electrical properties were investigated. For the $(Na_{0.47}K_{0.47}Sr_{0.03}Ca_{0.03})(Nb_{0.94}Ti_{0.06})O_3$-0.1 $MnO_2$ (NKN-SCT-$MnO_2$) ceramics sintered at temperatures of $1,025{\sim}1,100^{\circ}C$. The results indicated that all specimens were perovskite single phase formation without any second phase. It has been shown that relative density is increased to increasing sintering temperature. When the sintered temperature at $1,075^{\circ}C$, highest sintered density and maximum value of $4.45g/cm^3$. Average grain size is increased to increasing sintering temperature. The electromechanical coupling factor, dielectric constant, dielectric loss, d33 and curie temperature at the sintering temperature $1,075^{\circ}C$ of NKN-SCT-$MnO_2$ specimens were 0.22, 511, 0.033, 103 and $380^{\circ}C$, respectively.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2009년도 춘계학술대회 논문집
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• pp.436-438
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• 2009

In this study, in order to develop the composition of ceramics capable of being sintered at low temperature with high piezoelectric properties, PZW-PMN-PZT system ceramics for piezoelectric energy harvesting application were manufactured according to the amount of PZW addition. And also, their microstructural, dielectric and piezoelectric properties were investigated. At the sintering temperature of $930^{\circ}C$, a 5 mol% PZW substituted specimen showed a maximum value of density = $7.905g/cm^3$, kp = 0.585, $d_{33}$ = 351pC/N and Qm =1,254, respectively.

• Investigative Magnetic Resonance Imaging
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• 제18권1호
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• pp.52-58
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• 2014

목적: 임상용 MRI에서 마우스 종양의 pH 측정을 위한 $^1H-^{31}P$ RF 코일 시스템을 개발하고 팬텀을 이용하여 pH 값의 정확도를 시험하고자 한다. 대상과 방법: 마우스 종양 연구를 위한 표면형 $^1H$ 및 $^{31}P$ radio frequency (RF) 코일을 개발하였다. 두 코일을 서로 수직이 되도록 설치하여 두 코일간의 상호인덕턴스를 0으로 하였다. 다양한 pH 값을 가진 팬텀으로부터 $^{31}P$ MR 스펙트럼을 얻어 Henderson-Hasselbalch equation을 이용하여 pH를 구하였다. $^{31}P$ 스펙트럼으로부터 얻은 pH값은 pH meter를 사용하여 직접 구한 pH값과 비교한다. 결과: $^1H-^{31}P$ RF 코일 상호간 coil coupling (S12)은 각각 -73.0, -62.3 dB로 충분히 분리 되었다. 균일한 팬텀으로부터 얻은 $^1H$ 영상의 signal-to-noise ratio (SNR)는 약 300 이상이며, in vivo 고해상도 마우스 영상을 얻을 수 있었다. $^1H$ 신호가 분리된 $^{31}P$ MR 스펙트럼으로부터 얻은 pH값은 pH meter로 직접 측정하여 얻은 값과 약 97% 상관관계를 가졌다. 결론: 본 연구에서 개발한 임상 MRI 장비용 $^1H-^{31}P$ RF 코일 시스템으로부터 정확한 pH를 구할 수 있었다. 본 코일 시스템은 31P 이외의 다른 핵 MRS 혹은 MRI에 적용 가능할 것으로 기대된다.

• 센서학회지
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• 제10권1호
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• pp.62-70
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• 2001

CBD방법으로 성장하여 $450^{\circ}C$로 열처리한 ZnSe 박막은 회전 무늬로부터 외삽법으로 구한 격자상수 $a_0$가 $5.6678\;{\AA}$인 zinc blend임을 알았다. Van der Pauw 방법으로 측정한 Hall 데이터에 의한 이동도는 10 K에서 150 K 까지는 불순물 산란 (impurity scatterimg)에 의하여, 150 K에서 293 K까지는 격자산란 (lattice scattering)에 의하여 감소하는 경향을 나타냈다. 또한 운반자 농도의 ln n대 1/T에서 구한 활성화 에너지($E_a$)는 0.27 eV였다. 투과 곡선의 투과단으로 본 띠 간격은 293 k에서 $2,700{\underline{5}}\;eV$이었던 것이 10K에서는 $2.873{\underline{9}}\;eV$로 변하였다. 광전류 봉우리 위치를 투과단과 비교할 때 293 K에서 30 K까지 관측된 한 개의 봉우리는 가전자대 ${\Gamma}_8$에서 전도대 ${\Gamma}_6$로 전이에 의한 광전류 봉우리이고, 10K에서 관측된 단파장대 417.3 nm($2.971{\underline{4}}\;eV$)의 봉우리는 가전자대 ${\Gamma}_7$에서 전도대 ${\Gamma}_6$로, 431.5 nm($2.873{\underline{3}}\;eV$)의 봉우리는 가전자대 ${\Gamma}_8$에서 전도대 ${\Gamma}_6$로 전이에 의한 광전류 봉우리가 관측된 것으로 판단된다. 광전류 봉우리의 10K에서 단파장대의 가전자대 갈라짐(splitting)에 의해서 측정된 ${\Delta}so$(spin orbit coupling)는 $0.098{\underline{1}}\;eV$ 였다. 10 K에서 광발광 봉우리의 440.7 nm($2.812{\underline{7}}\;eV$)는 자유 엑시톤(free exciton : $E_x$), 443.5 nm ($2.795{\underline{5}}\;eV$)는 주개-얽매인 엑시톤(donor-bound exciton) 인 $I_2(D^0,\;X)$와 445.7 nm ($2.781{\underline{8}}\;eV$)는 반개-얽매인 엑시톤(acceptor-bound exciton) 인 $I_1(A^0,X)$이고, 460.5 nm ($2.692{\underline{3}}\;eV$)는 주개-받개쌍(donor-acceptor pair:DAP) 발광, 580 nm ($2.137{\underline{6}}\;eV$)는 self activated(A)에 기인하는 광발광 봉우리로 분석된다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 D
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• pp.1723-1725
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• 1999

This paper is the study for piezoelectric properties of PMN-PT-PZ composition for high power piezoelectric device. It needs the properties such as high mechanical quality factor(Qm), high electromechanical coupling coefficient(kp) and high dielectric strain constant$(d_31)$, and the stable electromechanical properties under high vibration level. For acquiring this results, the value of x is changed in 0.1Pb$(Mn_{1/3}Nb_{2/3})O_3$+(0.9-x)$PbZrO_3+xPbTiO_3$ composition to find MPB(morphotropic phase boundary), and the piezoelectric constants is measured by resonance-antiresonance frequency method, based on IRE Standard. Also, it is measured as a function of the amount of additive, $Nb_2O_5$. When the composition is applied to high power device, the electromechanical properties is measured by laser vibrometer to confirm the reliablity under high vibration level. From these results, PMN-PT-PZ composition is shown excellent properties and capacity of application to high power device.

• Tribology and Lubricants
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• 제37권3호
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• pp.99-105
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• 2021

In this study, for a high-pressure turbine (HPT) of 800 MW class supercritical thermal-power plant, considering aerodynamic cross-coupling, we performed a rotordynamic logarithmic decrement (LogDec) stability analysis with various tilting pad journal bearing (TPJB) designs, which several steam turbine OEMs (original equipment manufacturers) currently apply in their supercritical and ultra-supercritical HPTs. We considered the following TPJB designs: 6-Pad load on pad (LOP)/load between pad (LBP), 5-Pad LOP/LBP, Hybrid 3-Pad LOP (lower 3-Pad tilting and upper 1-Pad fixed), and 5-Pad LBPs with the design variables of offset and preload. We used the API Level-I method for a LogDec stability analysis. Following results are summarized only in a standpoint of LogDec stability. The Hybrid 3-Pad LOP TPJBs most excellently outperform all the other TPJBs over nearly a full range of cross-coupled stiffness. In a high range of cross-coupled stiffness, both the 6-Pad LOP and 5-Pad LOP TPJBs may be recommended as a practical conservative bearing design approach for enhancing a rotordynamic stability of the HPT. As expected, in a high range of cross-coupled stiffness, the 6-Pad LBP TPJBs exhibit a better performance than the 5-Pad LBP TPJBs. However, contrary to one's expectation, notably, the 5-Pad LOP TPJBs exhibit a slightly better performance than the 6-Pad LOP TPJBs. Furthermore, we do not recommend any TPJB design efforts of either increasing a pad offset from 0.5 or a pad preload from 0 for the HPT in a standpoint of stability.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.183-183
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• 2014

Recently, multiferroic materials gain much attention due to their fascinating fundamental physical properties. These materials offer wide range of potential applications such as data storage, spintronic devices and sensors, where both electronic and magnetic polarizations can be coupled. Among single-phase multiferroic materials, $BiFeO_3$ is typical because of the room-temperature magnetoelectric coupling in view of long-range magnetic- and ferroelectric-ordering temperatures. However, $BiFeO_3$ is well known to have large leakage current and small spontaneous polarization due to the existence of oxygen vacancies and other defects. Furthermore the magnetic moment of pure $BiFeO_3$ is very weak owing to its antiferromagnetic nature. Recently, various attempts have been performed to improve the multiferroic properties of $BiFeO_3$ through the co-doping at the A and the B sites, by making use of the fact that the intrinsic polarization and magnetization are associated with the lone pair of $Bi^{3+}$ ions at the A sites and the partially-filled 3d orbitals of $Fe^{3+}$ ions at the B sites, respectively. In this study, $BiFeO_3$, $Bi_{0.9}Ho_{0.1}FeO_3$, $BiFe_{0.97}Ni_{0.03}O_3$ and $Bi_{0.9}Ho_{0.1}Fe_{0.97}Ni_{0.03}O_3$ bulk compounds were prepared by solid-state reaction and rapid sintering. High-purity $Bi_2O_3$, $Ho_2O_3$, $Fe_2O_3$ and $NiO_2$ powders with the stoichiometric proportions were mixed, and calcined at $500^{\circ}C$ for 24 h to produce the samples. The samples were immediately put into an oven, which was heated up to $800^{\circ}C$ and sintered in air for 1 h. The crystalline structure of samples was investigated at room temperature by using a Rigaku Miniflex powder diffractometer. The field-dependent and temperature-dependent magnetization measurements were performed with a vibrating-sample magnetometer and superconducting quantum-interference device.

• Bulletin of the Korean Chemical Society
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• 제35권10호
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• pp.3041-3046
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• 2014

Blue emitting materials, 9,10-bis-biphenyl-4-yl-anthracene (AC-P), 9,10-bis-[1,1';4',1"]terphenyl-4-yl-anthracene (AC-DP), and 9,10-bis[3",5"-deiphenyltriphenyl-4'-yl]anthracene (AC-TP) were synthesized through boration and Suzuki aryl-aryl coupling reaction. EL performance of blue light-emitters was optimized and improved by varying the chemical structures of the side groups. In the thin film state, the three materials exhibit $PL_{max}$ values in the range of 442-456 nm. EL device with the synthesized compounds in the following configuration was fabricated: ITO/4,4',4"-tris(N-(2-naphthyl)-N-phenylamino)triphenylamine (2-TNATA) 60nm/N,N'-bis (naphthalene-1-yl)-N,N'-bis(phenyl)benzidine (NPB) 15nm/synthesized blue emitting materials (30nm)/1,3,5-tri(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl (TPBi) 20nm/LiF 1nm/Al 200nm. The current efficiency and C.I.E. value of AC-TP were 3.87 cd/A and (0.15, 0.12). A bulky and non-planar side group helps to prevent ${\pi}-{\pi}^*$ stacking interaction, which should lead to the formation of more reliable amorphous film. This is expected to have a positive effect on the high efficiency of the operating OLED device.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.533-538
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• 2001

The ZnSe sample grown by chemical bath deposition (CBD) method were annealed in Ar gas at 450$^{\circ}C$ Using extrapolation method of X-ray diffraction pattern, it was found to have zinc blend structure whose lattice parameter a$\_$o/ was 5.6687 ${\AA}$. From Hall effect, the mobility was likely to be decreased by impurity scattering at temperature range from 10 K to 150 K and by lattice scattering at temperature range from 150 K to 29 3K. The band gap given by the transmission edge changed from 2.7005 eV at 293 K to 2.8739 eV at 10 K. Comparing photocurrent peak position with transmission edge, we could find that photocurrent peaks due to excition electrons from valence band, $\Gamma$$\_$8/ and $\Gamma$$\_$7/ to conduction band $\Gamma$$\_$6/ were observed at photocurrent spectrum. From the photocurrent spectra by illumination of polarized light on the ZnSe thin film, we have found that values of spin orbit coupling splitting Δso is 0.0981 eV. From the PL spectra at 10 K, the peaks corresponding to free bound excitons and D-A pair and a broad emission band due to SA is identified. The binding energy of the free excitons are determined to be 0.0612 eV and the dissipation energy of the donor -bound exciton and acceptor-bound exciton to be 0.0172 eV, 0.0310 eV, respectively.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 하계학술대회 논문집
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• pp.235-235
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• 2009

This paper describes the influence of a polycrystalline (poly) 3C-SiC buffer layer on the surface acoustic wave (SAW) properties of poly aluminum nitride (AlN) thin films by comparing the center frequency, insertion loss, the electromechanical coupling coefficient ($k^2$), andthetemperaturecoefficientoffrequency(TCF) of an IDT/AlN/3C-SiC structure with those of an IDT/AlN/Si structure, The poly-AlN thin films with an (0002)-preferred orientation were deposited on a silicon (Si) substrate using a pulsed reactive magnetron sputtering system. Results show that the insertion loss (21.92 dB) and TCF (-18 ppm/$^{\circ}C$) of the IDT/AlN/3C-SiC structure were improved by a closely matched coefficient of thermal expansion (CTE) and small lattice mismatch (1 %) between the AlN and 3C-SiC. However, a drawback is that the $k^2(0.79%)$ and SAW velocity(5020m/s) of the AlN/3C-SiC SAW device were reduced by appearing in some non-(0002)AlN planes such as the (10 $\bar{1}$ 2) and (10 $\bar{1}$ 3) AlN planes in the AlN/SiC film. Although disadvantages were shown to exist, the use of the AlN/3C-SiC structure for SAW applications at high temperatures is possible. The characteristics of the AlN thin films were also evaluated using FT-IR spectra, XRD, and AFM images.