• Bulletin of the Korean Chemical Society
• /
• 제16권6호
• /
• pp.539-542
• /
• 1995

The crystal structure of K92-X (K92Al92Si100O384), a=25.128(1) Å, dehydrated at 360 ℃ and 2X 10-6 Torr, has been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd&bar{3} at 21(1) ℃. The structure was refined to the final error indices R1=0.044 and Rw=0.039 with 242 reflections for which I<3σ(I). In this structure, ninety-two K+ ions are located at the five different crystallographic sites. Sixteen K+ ions are located at the centers of the double six rings (site I; K(1)-O(3)=2.65(2) Å and O(3)-K(1)-O(3)=92.0(6)°). About twelve K+ ions lie at site I' in the sodalite cavity opposite double six rings (D6R's) and these K+ ions are recessed ca. 1.62 Å into the sodalite cavity from their O(3) plane (K(2)-O(3)=2.74(2) Å, O(3)-K(2)-O(3)=88.5(8)°). About thirty-two K+ ions are located at the site II in the supercage and these K+ ions are recessed ca. 1.20 Å into the supercage from their O(2) plane (K(3)-O(2)=2.64(2) Å, and O(2)-K(3)-O(2)=101(1)°). About twenty-two K+ ions lie at the site III in the supercage opposite 4-ring ladder and the remaining ten K+ ions lie at the site III' near the 4-ring ladder in the supercage (K(4)-O(4)=2.88(3) Å, O(4)-K(4)-O(4)=79.8(9)°, K(5)-O(4)=2.8(2) Å, and O(4)-K(5)-O(4)=68(5)°).

• 마이크로전자및패키징학회지
• /
• 제26권4호
• /
• pp.113-118
• /
• 2019

In this study, we investigated the growth of single-crystallinity α-Ga₂O₃ thin films on c-plane sapphire substrates using halide vapor pressure epitaxy. We also found the optimal growth conditions to suppress the phase transition of α-Ga₂O₃. Our results confirmed that the growth temperature and partial pressure of the reactive gas greatly influenced the crystallinity. The optimal growth temperature range was about 460~510℃, and the α-Ga₂O₃ thin films with the highest crystallinity were obtained at a III/VI ratio of 4. The thickness and surface morphology of the thin films was observed by scanning electron microscopy. The film thickness was 6.938 ㎛, and the full width at half maximum of the ω-2θ scan rocking curve was as small as 178 arcsec. The optical band gap energy obtained was 5.21 eV, and the films were almost completely transparent in the near-ultraviolet and visible regions. The etch pit density was found to be as low as about 6.0 × 10⁴ cm^-2.

• 한국재료학회지
• /
• 제11권10호
• /
• pp.889-894
• /
• 2001

2wt% $Al_2O_3-doped$ ZnO (AZO) thin films were deposited on sapphire (0001) single crystal substrate by parellel type rf magnetron sputtering at 55$0^{\circ}C$. The as-grown AZO thin films was polycrystalline and showed only broad deep defect-level photoluminescence (PL). In order to examine the change of PL property, AZO thin films were annealed in $N_2$ (N-AZO) and $H_2$ (H-AZO) at the temperature of $600^{\circ}C$~$1000^{\circ}C$ through rapid thermal annealing. After annealed at $800^{\circ}C$, N-AZO shows near band edge emission (NBE) with very small deep-level emission, and then N-AZO annealed at $900^{\circ}C$ shows only sharp NBE with 219 meV FWHM. In Comparison with N-AZO, H-AZO exhibits very interesting PL features. After $600^{\circ}C$ annealing, deep defect-level emission was quire quenched and NBE around 382 nm (3.2 eV) was observed, which can be explained by the $H_2$passivation effect. At elevated temperature, two interesting peaks corresponding to violet (406 nm, 3.05 eV) and blue (436 nm, 2.84 eV) emission was firstly observed in AZO thin films. Moreover, peculiar PL peak around 694 nm (1.78 eV) is also firstly observed in all the H-AZO thin films and this is believed good evidence of hydrogenation of AZO. Based on defect-level scheme calculated by using the full potential linear muffin-tin orbital (FP-LMTO), the emission 3.2 eV, 3.05 eV, 3.84 eV and 1.78 eV of H-AZO are substantially deginated as exciton emission, transition from conduction band maximum to $V_{ Zn},$ from $Zn_i$, to valence band maximum $(V_{BM})$ and from $V_{o} to V_BM}$, respectively.

• 한국결정학회지
• /
• 제8권1호
• /
• pp.38-47
• /
• 1997

새로운 방식의 결정성장용 직경 자동제어장치를 개발하였다. 이 장치는 금속선의 장력 변화를 주파수로 변환시켜 감지하는 무게센서로서 신호전달 및 전력공급 체계가 무접촉 방식이므로 노이즈가 극소화되며 따라서 안정성, 정밀성이 종래의 센서에 비해 10배 이상 증대된다. 이 장치에서 무게센서 부분은 1) 금속선, 2) 시그날을 형성하는 Sinusoidal Wave Generator, 3) 형성된 시그날의 진폭을 조정하고 안정화 시켜주는 자동 증폭조절회로, 4) 정류장치 및 신호 변환기, 5) 시그날을 관리, 제어하는 PC 보드 등으로 구성하였고, 그 외에 2개의 검증용, 무게보정용, 성장제어용 등 4개의 프로그램을 작성하였다. 이 장치는 표준편차 값이 $\pm0.10g$(1회/sec 측정 때), 분해능이 $5{\times}10^{-5}$이고, 최대 200kg까지 결정을 성장시킬 수 있으며, 또한 압력조건은 진공조건부터 200 atm 이하, 온도조건은 $350^{\circ}C$ 이하에서 일관성, 재현성 있는 작동이 가능했다. 단결정 자동직 경제어에 필요한 정확도를 확보하기 위해 온도범위 $100^{\circ}C$가 $\pm0.025^{\circ}C$로자동 조절되도록 '시그날 Divider'를 제작하였다. 이 무게 센서를 $Y_3Sc_2Ga_3O_{12},\;Er-Y_3Sc_2Al_3O_{12},\;Bi_{12}GeO_{20}$ 등의 단결정 성장에 응용하였으며 매우 양호한 결정을 성공적으로 성장시킬 수 있었다.

• 공업화학
• /
• 제9권4호
• /
• pp.481-485
• /
• 1998

마이크로파 열원을 이용하여 황산 용액에서 카올린을 가열 반응시켜 무기고분자인 수화 황산 알루미늄을 합성하였다. 하소된 카올린으로부터 알루미나의 최대 추출율은 재래식 열공정 ($80^{\circ}C$, 1 M 및 240분)에서 72.8%이었고, 마이크로파 공정 ($90^{\circ}C$, 1 M 및 60분)에서 99.9%이었다. 재래식 열공정에서와는 달리 마이크로파 공정에서 추출 합성된 수화 황산 알루미늄 시료는 빠른 결정립 성장에 의해 거대 크기의 판상으로 이루어진 층상구조로 존재하였다. 마이크로파와 재래식 열공정에서 합성하여, $1100^{\circ}C$에서 하소된 시료들을 모두 구형으로 응집된 분말상의 ${\gamma}-Al_2O_3$ 존재하였고, 이 시료들의 비표면적은 각각 113.5와 $106.6m^2/g$이었고, 입자의 평균 입경은 각각 46.5와 $26.3{\mu}m$이었다.

• Bulletin of the Korean Chemical Society
• /
• 제28권2호
• /
• pp.251-256
• /
• 2007

The crystal structure of fully dehydrated partially Cs+-exchanged zeolite X, [Cs52Na40Si100Al92O384], a = 24.9765(10) A, has been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd3 at 21 °C. The crystal was prepared by flow method for 5 days using exchange solution in which mole ratio of CsOH and CsNO3 was 1 : 1 with total concentration of 0.05 M. The crystal was then dehydrated at 400 °C and 2 × 10-6 Torr for 2 days. The structure was refined to the final error indices, R1 = 0.051 and wR2 (based on F2) = 0.094 with 247 reflections for which Fo > 4σ (Fo). In this structure, about fifty-two Cs+ ions per unit cell are located at six different crystallographic sites with special selectivity; about one Cs+ ion is located at site I, at the centers of double oxygen-rings (D6Rs), two Cs+ ions are located at site I', and six Cs+ ions are found at site II'. This is contrary to common view that Cs+ ions cannot pass sodalite cavities nor D6Rs because six-ring entrances are too small. Ring-opening by the formation of ?OH groups and ring-flexing make Cs+ ions at sites I, I', and II' enter six-oxygen rings. The defects of zeolite frameworks also give enough mobility to Cs+ ions to enter sodalite cavities and D6Rs. Another six Cs+ ions are found at site II, thirty-six are located at site III, and one is located at site III' in the supercage, respectively. Forty Na+ ions per unit cell are located at two different crystallographic sites; about fourteen are located at site I, the centers of D6Rs and twenty-six are also located at site II in the supercage. Cs+ ions and Na+ ions at site II are recessed ca. 0.34(1) A and 1.91(1) A into the supercage, respectively. In this work, the highest exchange level of Cs+ ions per unit cell was achieved in zeolite X by conventional aqueous solution methods and it was also shown that Cs+ ion could pass through the sixoxygen rings.

• 한국결정성장학회지
• /
• 제11권1호
• /
• pp.20-26
• /
• 2001

Ti와 B을 각각의 증발원으로 한 2원 전자빔 증착법으로 500$^{\circ}$의 기판온도에서 (100) Si 기판 위에 티타늄 붕화물 (${TiB}_{x}$) 박막을 증착시켰다. 이 방법은 여러 가지 boron-to-totanium ratio ($0{\le}B/Ti \le 2.5$)를 가지는 비당량 (${TiB}_{x}$ 박막의 표면 조도 역시 B/Ti비에 의존하여 변화되었다. 그리고 Pure Ti 박막은 (002)면의 우선 성장거동을 나타내었으나, $B/Ti{\ge}1.0$의 경우 (111)면의 우선 성장거동을 보이는 단일상의 TiB 박막이 성장되었다. 그러나 B농도가 더욱 증가됨에 따라 육방정계의 ${TiB}_{2}$상이 형성되기 시작하여 $B/Ti{\ge}2.0$ 의 조성비를 가지는 박막에서는 단일상의 ${TiB}_{2}$ 화합물을 나타내었다. 그리고 Si 기판상에 증착된 ${TiB}_{x}$ 박막의 잔류응력은 B/Ti비에 의존하나, 2원 전자빔 증착법으로 성장된 모든 박막에서 3~$20{\times}^9$dyn/$\textrm{cm}^2$ 정도의 인장응력을 나타내었다.

• 한국세라믹학회지
• /
• 제40권7호
• /
• pp.672-676
• /
• 2003

Y$_3$Fe$_{5}$O$_{12}$(YIG), $Y_3$Fe$_{5}$O$_{12}$(Bi:YIG), TbBi:YIG를 (GdCa)$_3$(GaMgZr)$_{5}$O$_{12}$ (SGGG)기판 위에 Liquid Phase Epitaxy (LPE)법으로 단결정 후막을 성장시켰다. 기판회전속도, 과냉도, 성장시간을 고정하여 치환되는 원소의 종류와 양에 따라 가네트 단결정의 격자상수, Bi 치환양, 표면형상, 자기적 특성을 조사하였다. TbBi:YIG 조성의 경우 격자상수는 12.500 $\AA$으로 기판의 격자상수인 12.496 $\AA$에 근접하게 나타났으며, 포화자계는 150 Oe로 향상된 결과가 나타났다.

• 한국재료학회지
• /
• 제25권8호
• /
• pp.423-428
• /
• 2015

Impedancemetric $NO_x$ (NO and $NO_2$) gas sensors were designed with a stacked-layer structure and fabricated using $LaCr_xCo_{1-x}O_3$ (x = 0, 0.2, 0.5, 0.8 and 1) as the receptor material and $Li_{1.3}Al_{0.3}Ti_{1.7}(PO_4)_3$ plates as the solid-electrolyte transducer material. The $LaCr_xCo_{1-x}O_3$ layers were prepared with a polymeric precursor method that used ethylene glycol as the solvent, acetyl acetone as the chelating agent, and polyvinylpyrrolidone as the polymer additive. The effects of the Co concentration on the structural, morphological, and $NO_x$ sensing properties of the $LaCr_xCo_{1-x}O_3$ powders were investigated with powder X-ray diffraction, field emission scanning electron microscopy, and its response to 20~250 ppm of $NO_x$ at $400^{\circ}C$ (for 1 kHz and 0.5 V), respectively. When the as-prepared precursors were calcined at $700^{\circ}C$, only a single phase was detected, which corresponded to a perovskite-type structure. The XRD results showed that as the Co concentration of the $LaCr_xCo_{1-x}O_3$powders increased, the crystal structure was transformed from an orthorhombic phase to a rhombohedral phase. Moreover, the $LaCr_xCo_{1-x}O_3$ powders with $0{\leq}x<0.8$ had a rhombohedral symmetry. The size of the particles in the $LaCr_xCo_{1-x}O_3$powders increased from 0.1 to $0.5{\mu}m$ as the Co concentration increased. The sensing performance of the stack-structured $LaCr_xCo_{1-x}O_3/Li_{1.3}Al_{0.3}Ti_{1.7}(PO_4)_3$ sensors was found to divide the impedance component between the resistance and capacitance. The response of these sensors to NO gas was more sensitive than that to $NO_2$ gas. Compared to other impedancemetric sensors, the $LaCr_{0.8}Co_{0.2}O_3/Li_{1.3}Al_{0.3}Ti_{1.7}(PO_4)_3$ sensor exhibited good reversibility and reliable sensingresponse properties for $NO_x$ gases.

• 한국세라믹학회지
• /
• 제40권3호
• /
• pp.317-321
• /
• 2003

The grain-boundary microcracking materials in the system A1$_2$Ti $O_{5}$ -ZrTi $O_4$(ZAT) is influenced by the thermal expansion anisotropy. The range of ZAT compositions investigated had showed very low thermal expansions of 0.3~1.3$\times$10$^{-6}$K compared to 8.29$\times$10$^{-6}$K of pure ZrTi $O_4$and 0.68$\times$10$^{-6}$K of polycrystalline A1$_2$Ti $O_{5}$ , respectively, compared with the theoretical thermal expansion coefficient for a single crystal of A1$_2$Ti $O_{5}$ , 9.70$\times$10$^{-6}$K. The low thermal expansion and microcraking temperature are apparently due to a combination of thermal contraction and expansion caused by the large thermal expansion anisotropy of the crystal axes of the A1$_2$Ti $O_{5}$ phase.