• Applied Microscopy
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• 제28권1호
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• pp.121-126
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• 1998

Detailed studies of high resolution TEM inages on the modulated structure caused by Zn vacancy ordering along [110] direction in BZT sintered at $1400^{\circ}C$ for 90 hours had revealed that the images which had hexagonal patterns were similar to those obtained from the structure which had no modulation, These images had appeared over the wide ranges from -30 nm to -42 nm in defocus values and from 2 nm to 20 nm in thickness. The computer simulated images showed that the modulation due to Zn vacancy ordering had made a small change in contrast in the interior of hexagonal pattern, which was very difficult to differenciate in experiments. The image which demonstrated the modulated structure very well was the one which obtained at -52 nm in defocus value and 16 nm in thickness.

• The Korean Journal of Ceramics
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• 제2권4호
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• pp.242-245
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• 1996

The microstructure of $Ba (Zn_{1/3}Ta_{2/3})O_3$ (BZT) was investigated using X-ray diffractometry(XRD) and transmission electron microscopy (TEM). $Ba_{0.5}TaO_3$ and $Ba_3TaO_{5.5}$ (BT) phasses were observed on the surface of the sintered specimen by XRD. Furthermore, a new type of ordering along the [110] direction was found in sintered specimen by the XRD and TEM analysis. The wavelength of ordering was 0.9 nm which is three times larger than the interplanar distance of (110) plane and new type of ordering is considered to be a result of Zn vacancy ordering. The creation of Zn vacancies and formation of BT phases are attributed to the evaporation of volatile ZnO. A new mechanism for ZnO loss is suggested. In this mechanism, only Zn vacancies are created only when the amount of ZnO loss is small and as the amount of ZnO loss increases, BT phases are formed at the same time. A new unit cell of ordered structure is suggested as the superlattics containing three BZT unit cells.

• Applied Microscopy
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• 제34권2호
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• pp.113-120
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• 2004

복합페로브스카이트 (1-x) $(Li_{1/2}Sm_{1/2})TiO_3-x (Na_{1/2}Sm_{1/2})TiO_3$ (LNST)의 미세구조를 TEM으로 관찰하였다. $0.0{\leq}x{\leq}0.6$ LNST에서는 A-site 양이온의 결핍에 의한 1/2 (001) 초격자 회절점을 형성하는 vacancy ordering을 갖고 있으며 이는 APB로 확인할 수 있었다. 그러나 x가 증가함에 따라 Li 이온의 양이 적어져서 vacancy ordering 을 만들기 어렵게 된다. $0.8{\leq}x{\leq}1.0$ 조성의 LNST의 미세구조에서도 APB가 관찰되었는데 이는 A-site에서 Na와 Sm 이온간의 1:1 chemical ordering에 의한 것으로 사료된다. LNST 전 조성에서 산소팔면체의 anti-phase tilting과 in-phase tilting 그리고 A-site 양이온의 antiparallel shift가 관찰되었는데, 이들은 ferroelastic domain으로 확인할 수 있었다.

• Applied Microscopy
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• 제27권2호
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• pp.217-223
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• 1997

New type of ordering along 1110] direction was found In BZT sintered at $1400^{\circ}C$ for 90 hours by using X-ray diffraction analysis and high resolution transmission electron microscopy. The wavelength of the modulated structure was 0.9 nm which is three times larger than the interplanar distance of (110) plane. New type of ordering is considered to be formed as a result of Zn vancacy ordering and new structural model was proposed. The computer simulated electron diffraction and the structural images are in good agreement with those obtained by experiments.

• 한국분말재료학회지
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• 제13권2호
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• pp.112-118
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• 2006

[ $R_{1/3}Sr_{2/3}FeO_{3}$ ](R=Pr, Nd, and Sm) was synthesized and their magnetic properties and charge ordering(CO) transition related with lattice dynamics and oxygen vacancy were systematically investigated. The charge disproportion ation(CD) in $R_{1/3}Sr_{2/3}FeO_{3}$(R=Pr,Nd) was in which two kins of iron with valence state $Fe^{3+}$ and $Fe^{5+}$ were found with ratio of 2:1. In this charge ordering state a sequence of $Fe^{3+}Fe^{3+}Fe^{5+}Fe^{3+}Fe^{3+}Fe^{5+}$ exists aligned along the [111] direction of the pseudocubic perovskite structure. The charge ordering exist in distorted structure involving $t_{pd}$ hybridization. The disordering phases coexist in distorted structure as temprature in creases that is controlled amount of oxygen vacancy. The magnetic hyperfine fields indicate charge tranfering temperature as it dissapeared drastically.

• Bulletin of the Korean Chemical Society
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• 제15권1호
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• pp.64-74
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• 1994

The nonstoichiometric chalcogenides with NaCl-type structure were prepared and the physical and structural properties were studied. The homogeneous range and the structural change were studied based on X-ray powder diffractions using Rietveld-type full-profile fitting technique. Wide homogeneous ranges were observed in Y-S and Y-Se systems, and relatively narrow homogeneous ranges were observed in Yb-S and Yb-Se systems. Both in $Yb_{1-x}S\;and\;Yb_{1-x}Se$, a vacancy ordering transition occurred in (111) plane direction. The ordered superstructure had cubic symmetry(Fm$\bar{3}m) with doubled unit cell "a" parameter compared to the original NaCl-type. The superlattice developed in a continuous second-order transitiion was characterized by the reduced waved vector k= $(a^*+b^*+c^*)/2$. Y-S system had metallic, and YSe, YbSe system had semiconducting properties in their homogeneous ranges. It was observed that the change of electronic transport properties in extended homogeneous range did not depend on the relativeratio of metal to nonmetal, but on the quantities of vacancies.

• Applied Microscopy
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• 제34권1호
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• pp.61-69
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• 2004

복합 페로브스카이트 (1-x) $(Li_{1/2}Sm_{1/2})TiO_3-x (Na_{1/2}Sm_{1/2})TiO_3$ (LNST) system의 마이크로파 유전특성과 미세구조를 XRD와 SEM을 이용하여 연구하였다. 이 LNST는 산소팔면체의 antiphase tilting 뿐만 아니라, inphase tilting과 양이온의 antiparallel shift를 가지는 구조변화는 보인다. 또한 LNST계는 $0.0{\leq}x{\leq}0.4$에서 양이온($Li^{+1}$)의 휘발이 일어나서 A-site vacancy ordering에 의해 c축으로 cell doubling이 일어난다. 미세구조의 관찰을 통해 전 범위의 조성에서 비정상 입성장 현상을 관찰하였다. LNST계에서 A-site에 $Li^{+1}$을 치환한 LST의 공진주파수 온도계수는 큰 음의 값($-220ppm/^{\circ}C$)을 가지나, $Na^{+1}$을 치환한 NST는 큰 양의 값($+173ppm/^{\circ}C$)을 가진다. x=0.4일때 4 GHz에서 ${\varepsilon}_r=103,\;Q*f_{0}=3,700GHz$ 그리고 $T_{cf}=+50ppm/^{\circ}C$의 좋은 유전특성을 얻었다.

• 한국전자현미경학회:학술대회논문집
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• 한국현미경학회 1996년도 제27차 추계학술대회
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• pp.20-23
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• 1996

• 대한화학회지
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• 제32권1호
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• pp.9-14
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• 1988

$La_{1-x}Ca_xFeO_{3-y}$ 계의 perovskite 형의 화합물은 La_2O_3,\;CaCO_3$, 및 Fe(NO-3)_3{\cdot}9H_2O$의 정량적 혼합물은 1100$^{\circ}C$에서 24시간 동안 가열하여 제조하였다. 이 고용체의 결정구조는 모든 조성에서 사방정계였다. X-선 회절분석과 Mohr 염 분석을 통하여 y값이 증가하면 공위배열에 의한 상전이가 일어나며 격자체적은 x값이 증가함에 따라 감소한다는 것을 확인하였다. 비화학양론적 조성 y는 0.0에서 0.5사이의 값을 나타내었다. Mossbauer 분광분석을 298K에서 수행하여 x = 0.75 조성이 높은 닐온도를 갖는다는 것을 확인하였다. 시료의 전기전도도는 $-100{\sim}100^{\circ}C$ 온도범위에서 측정하였다. 활성화 에너지로부터 공위 배열에 기인한 열린 통로를 갖고 있는 시료들은 이온성 전기전도에 의한 기여가 어느 정도 존재하는 것으로 밝혀졌다.

• The Korean Journal of Ceramics
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• 제5권4호
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• pp.371-374
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• 1999

Y2O3 and Nb2O5 co-doped tetragonal zirconia polycrystals((Y, Nb)-TZP) containing 10 to 30 vol% $Al_2O_3$ were prepared and hydrothermal stability of the composites was evaluated after aging for 5 h at the temperature range of $150^{\circ}C$ $250^{\circ}C$ under 4 MPa $H_2O$ vapor pressure in an autoclave. The (Y, Nb)-TZP/Al2O3 composites showed excellent phase stability under the hydrothermal conditions, as compared with the 3Y-TZP/$Al_2O_3$ composites, due to the combined effects of the Y-Nb ordering in the $t-ZrO_2$ lattice, the reduction of oxygen vacancy concentration, and the $Al_2O_3$ addition. The strength and fracture toughness of the (Y, Nb)-TZP/$Al_2O_3$ composite, containing 20 vol% of 2.8 $Al_2O_3$ particles, were 700 MPa and 8.1 MP.$am^{1/2}$, respectively.