• 한국재료학회지
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• 제19권10호
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• pp.550-554
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• 2009

Unreported dielectrics based on the binary system of MgO-SiO$_2$ were investigated as potential candidates for microwave dielectric applications, particularly those demanding a high fired density and high quality factors. Extensive dielectric compositions having different molar ratios of MgO to SiO$_2$, such as 2:1, 3:1, 4:1, and 5:1, were prepared by conventional solid state reactions between MgO and SiO$_2$. 1 mol% of V$_2$O$_5$ was added to aid sintering for improved densification. The dielectric compositions were found to consist of two distinguishable phases of Mg$_2$SiO$_4$ and MgO beyond the 2:1 compositional ratio, which determined the final physical and dielectric properties of the corresponding composite samples. The increase of the ratio of MgO to SiO$_2$ tended to improve fired density and quality factor (Q) without increasing grain size. As a promising composition, the 5MgO.SiO$_2$ sample sintered at 1400 $^{\circ}C$ exhibited a low dielectric constant of 7.9 and a high Q $\times$ f (frequency) value of $\sim$99,600 at 13.7 GHz.

• 한국결정성장학회지
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• 제29권6호
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• pp.298-307
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• 2019

본 연구에서는 Al₂O₃ 소결체 표면에 두 종류의 CaO-Al₂O₃-SiO₂(CAS) 계 유리 분말을 스프레이 코팅(spray coating) 후 소성 거동에 대하여 연구하였다; (1) Si-rich, SiO₂ 함량이 높은 유리, (2) Ca-rich, CaO 함량이 높은 유리. Ca-rich 유리는 점도가 약 10⁷~10⁹ poise일 때 유리 내부에 잔존하는 기포들의 심한 발포 현상이 일어났고 이에 따라 소결 방해에 따른 수축율이 감소하였으며 조도는 증가하였다. 반면, Si-rich 유리의 경우, 1000℃ 이하에서는 Ca-rich와 같은 심각한 발포현상은 없었으나, 1200℃에서 밀도가 낮은 크리스토발라이트(cristobalite) 결정 발생과 함께 기포의 재발포 현상이 일어나 수축율이 감소하였으며 조도가 증가하는 이상 소성 거동을 보였다. 이는 저밀도 크리스토발라이트 결정 생성으로 인한 유리질의 칼슘 함량 증가에 의한 점도 감소로 생각된다. 따라서 CAS계 유리의 경우 저온 소성에서는 발포 현상에 의한 표면조도 상승과 소결 방해를 고려해야 하며, 특히 SiO₂ 함량이 높을 경우, 고온에서 결정화에 의한 이상 발포 현상도 생각해야 한다.

• 한국광물학회지
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• 제30권3호
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• pp.127-136
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• 2017

자외선 차단기능과 제균 기능을 갖는 합성 $TiO_2$-복합체에 대해 압력의 영향을 체크하기 위해 고압실험을 시행하였다. 복합체 분말시료는 아나타제와 루틸 및 염화은으로 구성되어 있으며, 입자크기는 34 nm 정도로 결정되었다. 아나타제와 루틸 모두 약 14~16 GPa 구간에서 $ZrO_2$ (배델레이트)-형태의 결정구조로 상변이하며, 본 실험의 최고압력인 22.7 GPa까지 상변이는 계속된다. 압력을 모두 제거하여 상압 상태가 되면, 루틸은 ${\alpha}-PbO_2$ 구조로 상변이하며 아나타제는 고압의 $ZrO_2$-결정구조가 유지되는 것으로 판단된다. 염화은의 회절피크는 낮은 압력에서 사라지는 것이 관찰되었다.

• 한국세라믹학회지
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• 제49권6호
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• pp.631-636
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• 2012

Conventional SONOS (poly-silicon/oxide/nitride/oxide/silicon) type memory is associated with a retention issue due to the continuous demand for scaled-down devices. In this study, $Al_2O_3/Y_2O_3/SiO_2$ (AYO) multilayer structures using a high-k $Y_2O_3$ film as a charge-trapping layer were fabricated for nonvolatile memory applications. This work focused on improving the retention properties using a $Y_2O_3$ layer with different tunnel oxide thickness ranging from 3 nm to 5 nm created by metal organic chemical vapor deposition (MOCVD). The electrical properties and reliabilities of each specimen were evaluated. The results showed that the $Y_2O_3$ with 4 nm $SiO_2$ tunnel oxide layer had the largest memory window of 1.29 V. In addition, all specimens exhibited stable endurance characteristics (program/erasecycles up to $10^4$) due to the superior charge-trapping characteristics of $Y_2O_3$. We expect that these high-k $Y_2O_3$ films can be candidates to replace $Si_3N_4$ films as the charge-trapping layer in SONOS-type flash memory devices.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2017년도 춘계학술대회 논문집
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• pp.95.2-95.2
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• 2017

Anodic TiO2 nanostructures have wide applications due to their various functional properties such as wide band-gap, chemical stability, and anti-corrosiveness. In order to enhance the properties, several approaches to fabricate TiO2 structures have been developed. Especially, TiO2 nanotube arrays prepared by anodization in a fluoride electrolyte show impressive properties for dye sensitized solar cells1 and photocatalyst. In this presentation, we introduce new types of TiO2 nanostructures beyond TiO2 nanotubes that are fabricated by anodization at high temperature in a glycerol/phosphate electrolyte. We show that depending on the anodization parameters different self-organized morphologies - of highly aligned, high aspect ratio oxide structures can be formed. Critical factor for growth and the use for dye sensitized solar cells and photocatalyst will be discussed.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2001년도 추계 학술발표강연 및 논문개요집
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• pp.116-116
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• 2001

• Bulletin of the Korean Chemical Society
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• 제24권3호
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• pp.311-317
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• 2003

Vanadium oxides supported on zirconia and modified with MoO₃were prepared by adding Zr(OH)₄powder into a mixed aqueous solution of ammonium metavanadate and ammonium molybdate followed by drying and calcining at high temperatures. The characterization of prepared catalysts was performed using FTIR, Raman spectroscopy and solid-state $^{51}V$ NMR. In the case of a calcination temperature of 773 K, for samples containing low loading of $V_2O_5$, below 15 wt %, vanadium oxide was in a highly dispersed state, while for samples containing high loading of $V_2O_5$, equal to or above 15 wt %, vanadium oxide was well crystallized because the $V_2O_5$ loading exceeded the formation of a monolayer on the surface of $ZrO_2$. The $ZrV_2O_7$ compound was formed through the reaction of $V_2O_5\;and\;ZrO_2$ at 873 K and the compound decomposed into $V_2O_5\;and\;ZrO_2$ at 1073 K, which were confirmed by FTIR spectroscopy and solid-state $^{51}V$ NMR. IR spectroscopic studies of ammonia adsorbed on $V_2O_5-MoO_3/ZrO_2$ showed the presence of both Lewis and Bronsted acids.

• 한국결정성장학회지
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• 제8권4호
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• pp.573-580
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• 1998

MgO와 Al 분말을 자전고온연소합성법으로 $MgAl_2O_4$ 스피넬 상을 합성하였다. MgO 와 Al을 테르밋 반응으로 생성하였으며, 가열반응생성으로 $800^{\circ}C$ 예열온도에서 반응시켰다. DTA/TG, 합성생성물, 최고온도 공정조건에 대해 연구하였고, MgO와 Al은 MgO+2Al+ 3/$2O_3$ $\rightarrow$ $MgAl_2O_4$ 로 합성되었다. 미반응된 재료로부터 MgAl2O4 스피넬의 활성화 에너지는 -264.8kcal/mol의 발생열량과 5634K의 최고 반응온도로 계산되었다. 테르밋 반응후의 시험편의 체적느 6% 증가하였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 추계학술대회 논문집 Vol.16
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• pp.267-270
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• 2003

We have studied the interfacial diffusion phenomena and the role of ${\alpha}-Al_2O_3$ buffer layer as a diffusion barrier in the $Ba-ferrite/SiO_2$ magnetic thin films for high-density recording media. In the interface of amorphous Ba-ferrite ($1900-{\AA}-thick)/SiO_2$ thin film during annealing, the interfacial diffusion started to occur at ${\sim}700^{\circ}C$. As the annealing temperature increased up to $800^{\circ}C$, the interfacial diffusion abruptly proceeded resulting in the high interface roughness and the deterioration of the magnetic properties. In order to control the interfacial diffusion at the high temperature, we introduced ${\alpha}-Al_2O_3$ buffer layer ($110-{\AA}-thick$) in the interface of $Ba-ferrite/SiO_2$ thin film. During the annealing of $Ba-ferrite/{\alpha}-Al_2O_3/SiO_2$ thin film even at ${\sim}800^{\circ}C$, the interface was very smooth. The smooth interface of the film was also clearly shown by the cross-sectional FESEM. The magnetic properties, such as saturation magnetization 3nd intrinsic coercivity, were also enhanced, due to the inhibition of interfacial diffusion by the ${\alpha}-Al_2O_3$ buffer layer. Our study suggests that the ${\alpha}-Al_2O_3$ buffer layer act as a useful interfacial diffusion barrier in the $Ba-ferrite/SiO_2$ thin films.

• 센서학회지
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• 제29권6호
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• pp.407-411
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• 2020

In this study, we propose an array-type gas sensor with high selectivity and response using multiple oxide semiconductors. The sensor array was composed of SnO₂ and In₂O₃, and the detection characteristics were improved by using Pt, Au, and Pd catalysts. All samples were deposited directly on the Pt interdigitated electrode (IDE) through the e-beam evaporator glancing angle deposition (GAD) method. They grew in the form of well-aligned nanorods at off-axis angles. The prepared SnO₂ and In₂O₃ nanorod samples were exposed to CH₃COCH₃, C₇H₈, and NO₂ gases in a 300℃ dry condition. Au-decorated SnO₂, Au-decorated In₂O₃, and Pd-decorated In₂O₃ exhibited high selectivity for CH₃COCH₃, C₇H₈, and NO₂, respectively. They demonstrated a high detection limit of the sub ppb level computationally. In addition, measurements from each sensor were executed in the 40% relative humidity condition. Although there was a slight reduction in detection response, high selectivity and distinguishable detection characteristics were confirmed.