• 한국세라믹학회지
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• 제32권3호
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• pp.295-304
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• 1995

Stabilization of the perovskite phase and sequence of reactions occuring during calcination were studied with solid solutions formed between Pb(Zn1/3Nb2/3)O3 and Pb(Fe1/2Nb1/2)O3. In the PZN-PFN composition of equal molar ratio, rhombohedral type pyrochlore phase (Pb2Nb2O7) and PbO-rich distorted cubic type pyrochlore phase (Pb3Nb2O8) were coexisted as intermediate phases at temperatures below 85$0^{\circ}C$, and these phases transformed to a stable cubic type pyrochlore phase, Pb3Nb4O13 solid solution and a perovskite solid solution at temperatures above 85$0^{\circ}C$. The major stable phase as increasing sintering temperatures was a perovskite phase in this binary system and prominent suppression of the pyrochlore phase was achieved by substituting Zn2+ with Fe3+ or by increasing sintering temperature. The composition containing 20mol% PZN possessed the best dielectric properties, and the dissipation factor was lower than 5% in all compositions.

• Bulletin of the Korean Chemical Society
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• 제21권7호
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• pp.679-684
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• 2000

The Sr2Co0.5Nb(Ta)0.5O4 and Sr3CoNb(Ta)O7 compounds, both with Ruddlesden-Popper structures, have been synthesized by the ceramic method at $1150^{\circ}C$ under atmospheric pressure. The crystallographic structure of the compounds was assigned to the tetr agonal system with space group 14/mmm by X-ray diffraction(XRD) Rietveld refinement. The reduced lattice volume and lattice parameters increased as the Ta with 5d substitutes for the Nb with 4d in the compounds. The Co/Nb(Ta)O bond length has been determined by X-ray absorption spectroscopic(EXAFS/XANES) analysis and the XRD refinement. The CoO6,octahedra were tetragonally distorted by elongation of Co-O bond along the c-axis. The magnetic measurement shows the compounds Sr2Co0.5Nb(Ta)0.5O4 and Sr3CoNb(Ta)O7 have paramagnetic properties and the Co ions with intermediate spin sates between high and low spins in D4h symmetry. All the compounds showed semiconducting behavior whose electrical conductivity increased with temperature up to 1000 K. The electrical conductiviy increased and the activation energy for the conduction decreased as the number of perovskite layers increased in the compounds with chemical formula An+1BnO3n+1.

• 한국전기전자재료학회논문지
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• 제16권4호
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• pp.317-321
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• 2003

In this study, the structural properties were Investigated for the deposited (Ba,Sr)(Nb,Ti)O$_3$[BSNT] thin films grown on Pt/TiO$_2$/SiO$_2$/Si substrate by RF sputtering method. The structural properties of the BSNT thin films affected by the Ar/02 ratios were Investigated. In the case of the BSNT thin films deposited with condition of 60/40(Ar/O$_2$) ratio, the BaTiO$_3$, SrTiO$_3$ and BaNbO$_3$ phases were showed. The composition ratio of Nb and Ti in the BSNT thin films were nearly equivalent. Also, in the BSNT thin films deposited with condition of 60/40 and 80/20(Ar/O$_2$) ratios, the composition of Ba, Sr, Nb and Ti were relatively uniform. The Ba, Sr, Nb and Ti in the BSTN thin films were not diffused into the Pt layer.

• 한국세라믹학회:학술대회논문집
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• 한국세라믹학회 2003년도 추계총회 및 연구발표회 초록집
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• pp.204.1-204
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• 2003

• 한국결정학회지
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• 제4권2호
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• pp.74-85
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• 1993

Lithium niobate(LiNbO3) 단결정은 유전성, 압전성, 초전성, 비선형 광학 및 선형 전기광학 물질로서 다양한 응용 성을 가지고 있으므로 전기와 광학장치로 널리 사용되어지고 있다. 그러나 LiNbo3 단결정이 레이저를 이용한 광학장치로 응용될 때 레이저광의 세기에 따라 상굴절(ne)과 이상굴절(no)이 불규칙하게 변하는 장손상이 발생하여 비선 형 광학소자로의 이용에 한계가 있음이 밝혀졌다. 1980년 Zhong등이 LiNbO3에 MgO를 4.5mol% 첨가한 MgO:LiNbO3단결정을 성장시켜 물성을 조사한 결과 광손 상이 현저하게 감소된다고 발표한 후 이 분야의 연구가 활발히 진행되고 있다. 본 연구에서는 순수한 LiNbO3 단결정의 최적 성장조건인 congrugnt한 LiNbOs(Li/Nb=0.486)에 MgO를 0, 2.5, 5.0, 7.5, 10.0 mol% 첨가시킨 MgO:LiNb03 단결정을 Czochalski법으로 성공적으로 성장시켰다. 결정성장은 성장온도 1250℃ 근방에서 회전속도 15rpm 인상속도 2.85 ∼3.25 mm/hr로 하였으며 냉각율은 30℃/hr이다. 성장시킨 단결정의 X-ray 회절실험과 편광현미경의 conoscope상 관찰로 양질의 MgO:LiNbO3 단결정이 성장되었음을 확인하였다. c축에 수직되게 절단한 c-pltae 시료 중 MgO가 첨가된 MgO:LiNb03 시료에서 나이테 형태의 둥근 원무늬가 나타나고 있다. 이 현상은 결정성장시 공기 중의 산소분압에 의해 MgO:LiNbO3 의 용융상태에서 MgO가 균일하게 분포되지 못하기 때문에 나타난 것으로 해석 된다. MgO 첨가량에 따른 MgO:LiNbo3 단결정의 결정 결함 구조를 조사하기 위하여 밀도측정을 하였다. MgO:LiNbO3 단결정의 밀도는 MgO론 2.5mol% 첨가한 시료에서 감소 하다가 5.0mol% 첨가한 시료에서 다시 증가하였으며 5.0mol%이상에서는 다시 감소하였다. 이 실험결과로 MgO 첨가량에 따른 결정 결함구조를 점 결함 모형 (point defect medel)으로 해석하였다.

• 한국재료학회지
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• 제9권10호
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• pp.1025-1031
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• 1999

6종류의 조성을 가진 TiAl계 합금, 즉 Ti-(42, 44)Al-2Nb-4V, Ti-(42, 44)Al-4Nb-2V 및 Ti-(42, 44)Al-4Nb-2Cr을 아크용해법으로 제조한 후, 이들의 산화성질을 조사하였다. 700, 800 및 $900^{\circ}C$의 대기 중, 50시간동안의 등온 및 반복 산화실험으로부터, 산화저항은 Ti-(42, 44)Al-2Nb-4V, Ti-(42, 44)Al-4Nb-2V 및 Ti-(42, 44)Al-4Nb-2Cr의 순으로 증가함을 알 수 있었다. 내산화성에서 V은 해로운 원소이고 Cr은 유익한 원소이었다. 산화 중 모든 모재 구성원서는 외부확산하였고 분위기중으로 부터의 산소는 내부확산하는 상호확산이 관찰되었으며, 생성되는 산화물은 최외각 $\textrm{TiO}_2$층, 상부 ($\textrm{TiO}_2+\textrm{Al}_2\textrm{O}_3$) 혼합층 및 하부 $\textrm{TiO}_2$-잉여층으로 이루어진 3층 산화물구조로 구성되어 있었다.

• 한국결정성장학회지
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• 제1권1호
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• pp.1-4
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• 1991

The applicability of $LiNbO_{3}$ as a substrate for fabrication of Ti-indiffused waveguide electro-optic devices is limited. Ti diffuses comparatively in congruently melting $LiNbO_{3}$; the Curie temperature of this material is too low to permit diffusion temperatures much above $1100^{\circ}C$ without the necessity of re-poling the crystal. Both of hese difficulties could be eliminated by incorporating certain dopants in $LiNbO_{3}$. Crystals of $LiNbO_{3}$ doped with Ti and Mg were grown and evaluated. The electroptic coefficients and birefringence of $LiNbO_{3}$ doped crystals were measured at ${\lambda}=.6328$ and $1.32\;$\mu{m}$. Curie temperatures were measured. The Curie temperature of both undoped and Ti-doped $LiNbO_{3}$ was $1130^{\circ}C$; that for Mg-doped $LiNbO_{3}$ was $30^{\circ}$ higher. From these data, a composition for the crystals was estimated. Thermogravimetric data confirmed this estimate and showed that the composition of Mg : $LiNbO_{3}$ was $49.3{\pm}0.2mole%\;Li_{2}O$ ; the composition of the undoped and Ti : $LiNbO_{3}$ samples was $48.6{\pm}0.2mole%$. Diffusion of Ti into both Mg-doped and Ti-doped $LiNbO_{3}$ crystals was studied as a function of $Li/NbO_{3}$ ratio and temperature.

• 한국표면공학회지
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• 제50권3호
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• pp.206-211
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• 2017

$BiNbO_4:RE^{3+}$ (RE = Dy, Eu, Sm, Tb) phosphors were prepared by solid-state reaction at $1100^{\circ}C$ and their structural, photoluminescent, and morphological properties were investigated. XRD patterns exhibited that all the synthesized phosphors exhibited a triclinic system with a dominant (210) diffraction peak, irrespective of the type of activator ions. The surface morphologies of rare-earth-ion-doped $BiNbO_4$ phosphors were found to depend strongly on the type of activator ions. The $Eu^{3+}$ and $Dy^{3+}$ doped $BiNbO_4$ phosphors revealed a strong red (613 nm) emission resulting from the $^5D_0{\rightarrow}^7F_2$ transition of $Eu^{3+}$ and a dominant yellow (575 nm) emission originating from the $^4F_{9/2}{\rightarrow}^6H_{13/2}$ transition of $Dy^{3+}$ respectively, which were the electric dipole transitions, indicating that the activator ions occupy sites of non-inversion symmetry in the $BiNbO_4$ phosphor. The main reddish-orange emission spectra of $Sm^{3+}$-doped $BiNbO_4$ phosphors were due to the $^4G_{5/2}{\rightarrow}^6H_{7/2}$ (607 nm) magnetic dipole transition, indicating that the $Sm^{3+}$ ions were located at inversion symmetry sites in the $BiNbO_4$ host lattice. As for $Tb^{3+}$-doped phosphors, green emission was obtained under excitation at 353 nm and its CIE chromaticity coordinates were (0.274, 0.376). These results suggest that multicolor emission can be achieved by changing the type of activator ions incorporated into the $BiNbO_4$ host crystal.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 하계학술대회 논문집 Vol.8
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• pp.300-301
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• 2007

$Mg_4(Nb_{2-x}V_x)O_9$ (MNV) ceramics have been prepared by a hydrothermal method. Low-temperature sintering of $Mg_4(Nb_{2-x}V_x)O_9$ (MNV) by V substitution for Nb was discussed in this study. A $Q{\cdot}f_0$ value of 103,297 GHz with a ${\varepsilon}_r$ of 12.56 and a ${\tau}_f$ of $-10.53\;ppm/^{\circ}C$ was obtained when x=0.0625 after sintering at $1100^{\circ}C$ for 5 h.

• 한국전기전자재료학회논문지
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• 제11권3호
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• pp.208-213
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• 1998

Microwave dielectric properties of $BiNbO_4$ containing CuO and $V_2O_5$(BN ceramics). BN ceramic with 0.07wt% $V_2O_5$ and 0.03wt% CuO (BNC3V7) was sintered at $900^{\circ}C$ where it is possible for these to be co-fired with Ag electrode. The dielectric constant of 44.3, TCF (Temperature Coefficient of resonance Frequency) of 2 ppm/$^{\circ}$ and Q${\times}f_o$ value (product of Quality value and resonance Frequency) of 22,000GHz could be obtained from those ceramics. It is observed that orthorhombic structure was stable $1000^{\circ}C$. As sintering temperature increases, the dielectric properties decreased. The main reasons were abnormal grain growth and the main peak of triclinic moved from the main peak of orthorhombic.