• 한국자기학회지
• /
• 제8권4호
• /
• pp.203-209
• /
• 1998

Single phase garmet Y3-xBixFe5O12(x=0.0, 0.25, 0.5, 0.75, 1.0)을 ethylene glycol을 용매로 하여 sol-gel 법으로 합성후 x-ray diffraction, Mossbauer 분광기, vibrating sample magnetometer (VSM)를 이용하여 결정학적 및 자기적 특성을 연구하였다. Y과 Fe의 수화 반응을 통하여 얻은 Y3Fe5O12의 x-ray 회절 분석 결과는 결정구조가 cubic임을 알 수 있었고 Y에 Bi를 치환한 경우 또한 cubic 구조이었으며 Bi의 치환 량이 증가할수록 격자 상수가 선형적으로 증가함을 알수 있었다. Bi를 첨가한 Y3-xBixFe5O12 (x=0.0, 0.25, 0.5, 0.75, 1.0)의 단일상의 garnet이 형성되기 시작하는 온도는 80$0^{\circ}C$이고 secound phase (BiFeO3)가 생성되기 시작하는 온도는 x=0.75는 100$0^{\circ}C$이며 x-1.0은 95$0^{\circ}C$였다. Mossbauer 분광 실험과 VSM측정 결과 Birk 치환 될수록 포화 자화 값과 coercivity값이 감소하는 경향을 보였으며 Curic 온도는 Bi의 치환 양이 증가할수록 약간 증가하는 경향을 보임을 알 수 있었다.

• 한국자기학회지
• /
• 제9권5호
• /
• pp.234-238
• /
• 1999

각종 microwave용 통신기기 소자 및 고주파용 memory 소자로 사용하기 위해서 각형비가 크고 보자력이 작은 lithium ferrite를 개발하고 물리적인 특성을 조사하기 위하여 Li0.48-0.5xBi0.02Ni0.04ZnxFe2.46-0.5xO4의 조성식을 갖는 시편을 제조하였다. ZnO을 첨가하여 변화시킴에 따라 잔류자기(Bm)가 증가하고 보자력(Hc)이 낮아졌으나 각형비 R은 감소하였다. 105$0^{\circ}C$에서 소결한 시편의 경우 R=0.82, Hc=1.8Oe로 나타났고 110$0^{\circ}C$에서 소결한 시편의 경우 R=0.75 및 Hc=1.70Oe인 값을 얻었다. Tc는 463$^{\circ}C$로 측정되었고 주변온도 변화에 대한 Br값의 변화가 매우 안정된 0.09~0.11 값으로 나타났다.

• 한국자기학회지
• /
• 제27권1호
• /
• pp.30-34
• /
• 2017

본 연구에서는 교환 결합력을 갖는 강자성/반강자성(AF) 박막에서 단자구 모델을 사용하여 교환 바이어스($H_{ex}$)의 각도 의존성을 계산하였으며, NiFe/MnIr 박막에서 측정한 결과와 비교 분석하였다. AF층 두께가 임계 두께 이상에서($t_{AF}$ > $t_c$) 계산한 $H_{ex}$의 각도 의존성은 전형적인 일방 이방성 특성을 보였으나, $0.5t_c$ < $t_{AF}$ < $t_c$에서는 $90^{\circ}$ 근처의 특정한 각도에서 AF 스핀의 고정에 의한 독특한 $H_{ex}$의 각도 의존성을 보였다. NiFe/MnIr(20 nm) 박막에서 측정한 $H_{ex}$의 각도 의존성은 전형적인 일방 이방성 특성을 보였으나, NiFe/MnIr(4 nm) 박막에서는 일방 이방성 특성과 AF 스핀의 고정에 의한 특성이 혼합된 결과를 보였으며, 이는 다결정 구조를 갖는 MnIr의 입도 분포 특성으로 설명되어짐을 알 수 있었다.

• 한국재료학회지
• /
• 제19권4호
• /
• pp.220-223
• /
• 2009

Lithium dihydrogen phosphate ($LiH_2PO_4$) powder was purchased from Aldrich Chemical Co. From the scanning electron microscope (SEM) observation, these polycrystals have dimensions in the range of $25-250{\mu}m$. The electrical conductivity was measured at a measuring frequency of 1 kHz on heating polycrystalline lithium dihydrogen phosphate ($LiH_2PO_4$) from room temperature to 493 K. Two anomalies appeared at 451 K ($T_{p1}$) and 469 K ($T_{p2}$). The electrical conductivity reached the magnitude of the superprotonic phases: $3{\times}10^{-2}{\Omega}^{-1}cm^{-1}$ at 451 K ($T_{p1}$) and $1.2{\times}10{\Omega}^{-1}cm^{-1}$ at 469 K ($T_{p2}$). It is uncertain whether the superprotonic phase transformations are due to polymorphic transitions in the bulk, surface transitions, or chemical reactions (thermal decomposition) at the surface. Considering several previous thermal studies (differential scanning calorimetry and thermogravimetry), our experimental results seem to be related to the last case: chemical reactions (thermal decomposition) at the surface with the progressive solid-state polymerization.

• 한국재료학회지
• /
• 제24권1호
• /
• pp.48-52
• /
• 2014

The Mg-enriched magnesium aluminum silicate (MAS) glass is known for its higher mechanical strength and chemical resistance. Among such glasses, cordierite ($Mg_2Al_4Si_5O_{18}$) is well known to have a low thermal expansion and low melting point. Polycrystalline engineering ceramics such as alumina can be strengthened by a surface modification with low thermal expansion materials. The present study involves the synthesis of cordierite by a sol-gel process and investigates the effect of glass penetration on the surface of alumina. The cordierite powders were prepared from $Al(OC_3H_7)_3$, $Mg(OC_2H_5)_2$ and tetraethyl orthosilicate by hydrolysis and condensation reaction. The cordierite powders were characterized by X-ray diffraction (XRD, Rigaku), scanning electron microscope (SEM, JEOL: JSM-5610), energy dispersive spectroscopy (EDS, JEOL: JSM-5610), and universal testing machine (UTM, INSTRON). The X-ray diffraction patterns showed that the synthesized particles were ${\mu}$-cordierite calcined at $1100^{\circ}C$ for 1 h. The shape of synthesized cordierite was changed from ${\mu}$-cordierite to ${\alpha}$-cordierite with increasing calcination temperature. Synthesized cordierite was used for surface modification of alumina. Cordierite powders penetrated deeply into the alumina sample along grain boundaries with increasing temperature. The results of surface modification tests showed that the strength of the prepared alumina sample increased after surface modification. The strength of a surface modified with synthesized cordierite increased the most, to about 134.6MPa.

• 한국재료학회지
• /
• 제24권1호
• /
• pp.19-24
• /
• 2014

We report the nitrogen monoxide (NO) gas sensing properties of p-type CuO-nanorod-based gas sensors. We synthesized the p-type CuO nanorods with breadth of about 30 nm and length of about 330 nm by a hydrothermal method using an as-deposited CuO seed layer prepared on a $Si/SiO_2$ substrate by the sputtering method. We fabricated polycrystalline CuO nanorod arrays at $80^{\circ}C$ under the hydrothermal condition of 1:1 morality ratio between copper nitrate trihydrate [$Cu(NO_2)_2{\cdot}3H_2O$] and hexamethylenetetramine ($C_6H_{12}N_4$). Structural characterizations revealed that we prepared the pure CuO nanorod array of a monoclinic crystalline structure without any obvious formation of secondary phase. It was found from the gas sensing measurements that the p-type CuO nanorod gas sensors exhibited a maximum sensitivity to NO gas in dry air at an operating temperature as low as $200^{\circ}C$. We also found that these CuO nanorod gas sensors showed reversible and reliable electrical response to NO gas at a range of operating temperatures. These results would indicate some potential applications of the p-type semiconductor CuO nanorods as promising sensing materials for gas sensors, including various types of p-n junction gas sensors.

• International Journal of Precision Engineering and Manufacturing
• /
• 제8권2호
• /
• pp.44-48
• /
• 2007

In recent years, the size of plane substrates and semiconductor wafers has increased. As conventional contact transportation systems composed of, for example, carrier rollers, belt conveyers, and robot hands carry these longer and wider substrates, the increased weight results in increased potential for fracture. A noncontact transportation system is required to solve this problem. We propose a new noncontact transportation system combining acoustic viscous and aerostatic forces to provide damage-free transport. In this system, substrates are supported by aerostatic force and transported by acoustic viscous streaming induced by traveling wave deformation of a disk-type stator. A ring-type piezoelectric transducer bonded on the stator excites vibration. A stator with a high Q piezoelectric transducer can generate traveling vibrations with amplitude of $3.2{\mu}m$. Prior to constructing a carrying road for substrates, we clarified the basic properties of this technique and stator vibration characteristics experimentally. We constructed the experimental equipment using a rotational disk with a 95-mm diameter. Electric power was 70 W at an input voltage of 200 Vpp. A rotational torque of $8.5\times10^{-5}Nm$ was obtained when clearance between the stator and disk was $120{\mu}m$. Finally, we constructed a noncontact transport apparatus for polycrystalline silicon wafers $(150(W)\times150(L)\times0.3(t))$, producing a carrying speed of 59.2 mm/s at a clearance of 0.3 mm between the stator and wafer. The carrying force when four stators acted on the wafer was $2\times10^{-3}N$. Thus, the new noncontact transportation system was demonstrated to be effective.

• 한국진공학회지
• /
• 제6권2호
• /
• pp.114-121
• /
• 1997

투명전도성 산화주석 박막이 펄스레이저증착에 의하여 파이렉스유리 기판상에 제조 되었다. 진공, $O_2$, 및 $Sn(CH_3)_4$분위기에서 Nd-YAG레이저 빛살이 다결정 $SnO_2$ 타겟을 융제 하여 실온에서 기판상에 박막을 증착시키고, 증착된 막을 230, 420, 및 $610^{\circ}C$에서 각각 2시 간 동안 공기중에서 열처리하였다. 박막의 특성이 UV-VIS-NIR 분광법과 X-선 회절법에 의하여 조사되고, 전기적 성질이 촉심식법으로 구해진 막의 두께와 함께 사점탐침법에 의하 여 측정되었다. $Sn(CH_3)_4$이 존재할 때 $SnO_2$상들이 실온에서조차 성장되는 것이 관찰되었다. 이는 레이저 융제 동안 발생된 마이크로플라즈마가 전구물질분자의 분해에 중요한 역할을 함을 시사한다.

• 한국재료학회지
• /
• 제1권2호
• /
• pp.77-85
• /
• 1991

LPCVD(Low Pressure Chemical Vapor Deposition) System을 이용하여 여러가지 증착 변수에 따른 실리콘 박막의 표면형상에 대해 고찰하였다. 중착압력, 중착온도, 반응기체의 유속에 따라 증착층의 표면형상이 큰 변화를 나타냈으며, 증착압력과 반응기체의 유속이 증가할수록 유효면적이 최대가 되는 증착온도가 증가하였다. 이러한 실험결과는 안정한 핵의 생성률이 최대가 될때 유효표면적이 최대가 된다는 가정으로부터 유도된 식과 일치하는 결과를 나타냈다.

• 한국재료학회지
• /
• 제1권2호
• /
• pp.93-98
• /
• 1991

The as-grown $YBa_2Cu_3O_{7-x}$ superconducting thin films on MgO(100) substrate have been prepared by a reactive coevaporation method. The superconducting transition temperature, surface morphology and crystalline quality were examined as a function of the substrate temperature ranging from $450^{\circ}C$ to $590^{\circ}C$. From the reflection high energy electron diffraction (RHEED) analysis, it was found the film consisted of almost amorphous phase with a halo pattern deposited at the substrate temperature of $450^{\circ}C$. The film deposited at the substrate temperature of $510^{\circ}C$ consisted of polycrystalline phase, showing a broad ring pattern. On the other hand, for the film deposited at $590^{\circ}C$, RHEED showed spotty pattern indicating that this film consisted of single crystal phase. It has rough film surface due to the surface outgrowth. The surface outgrowth increased as the substrate temperature increased from $510^{\circ}C$ to $590^{\circ}C$. the surface outgrowth may be due to the anisotropic growth rate. The highest transition temperature obtained in this study was $Tc_{zero}$ of 83K with $Tc_{onset}$ of 88K for the film deposited at $590^{\circ}C$ using activated RF oxygen plasma.