• Bulletin of the Korean Chemical Society
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• v.18 no.9
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• pp.972-976
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• 1997

Single phase ruthenium oxides with perovskite (ATi1-xRuxO3 (A=Ca, Sr)) and pyrochlore structure (Bi2Ru2O7, Pb2Ru2O6.5) have been prepared reproducibly by solid state reaction methods and their electrocatalytic activities for oxygen evolution have been examined by Tafel plots. Tafel slopes vary from a low value of 42 mV/decade up to 222 mV/decade at room temperature. The high exchange current densities and high Tafel slopes compared with those obtained from the RuO2 DSA electrode at the crystalline single phase metal oxide electrodes suggest that they are better electrocatalysts at low overpotentials. A favorable change in the Tafel slope for the oxygen evolution reaction occurs as the ruthenium content increases. Substitution of Ti for Ru in the perovskite solid solutions enhanced their chemical stability by losing marginal electrochemical activity.

• Journal of the Korean Chemical Society
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• v.40 no.9
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• pp.607-614
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• 1996

The structural changes and dielectric properties of Pb1-x(Na1/2La1/2)x(Mg1/3Nb2/3)O3 compounds substituted by 0∼50 mol.% of Na+/La3+ mixed ions were investigated by X-ray diffraction method, IR and Raman spectroscopy, and LCR meter. The amount of perovskite phase increased with the increases of Na+/La3+ substituents and sintering temperatures. Although the superlattice lines due to 1:1 ordering were not detected by X-ray diffraction method, it was found, from the Raman spectroscopy and the increase of diffuseness coefficient, that the ordering behavior was related to the decrease of A site ion size. Dielectric properties in Pb1-x(Na1/2La1/2)x(Mg1/3Nb2/3)O3 were affected by the amount of perovskite phase, grain size, and density. The phase transitions were broadened and phase transition temperatures were lowered by the increase of Na+/La3+ ions.

• Journal of the Korean Vacuum Society
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• v.7 no.1
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• pp.17-23
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• 1998

$Pb(Fe_{0.5}Nb_{0.5}O_3(PFN)$ thin films were prepared by rf magnetron co-sputtering method on $SiO_2/Si$, ITO/glass, and $Pt/Ti/SiO_2/Si$ substrates and post-annealed at the $N_2$ atmosphere by RTA(rapid thermal annerling). The degree of crystallinity of PFN films was identified on various substrates. Electrical properties of PFN films was characterized for $Pt/PFN/Pt/Ti/SiO_2/Si$ structure. The composition of PFN films was estimated by EPMA (electron probe micro analysis). PFN films would be crystallized better to perovskite phase on ITO/glass substrate than $SiO_2/Si$ substrate. This may be induced by the deformation of Pb deficient pyrochlore phase due to Pb diffusion into $SiO_2/Si$ substrate. PFN films on $Pt/Ti/SiO_2/Si$ substrate. PFN films with 5-10% Pb excess were crystallized to perovskite phase from $500^{\circ}C$ temperature. In summary, we show that Pb composition and annealing temperature were critically influenced on crystallinity to perovskite phase. When PFN film with 17% Pb excess was annealed at $600^{\circ}C$ at the $N_2$ atmosphere for 300kV/cm and 88. Its remnant polarization coercive field $2.0 MC/cm^2$ and 144kV/cm, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.11a
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• pp.271-274
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• 1998

Metallic ferromagnet LA$_{1-x}$ Sr$_{x}$MnO$_3$ has received considerable attentions because of its metallic conductivity and giant magnetic resistivity. It is generally believed that layered perovskite SrO(LA$_{1-x}$ Sr$_{x}$MnO$_3$)$_{n}$ phase is insulating and shows no metallic transition. But recent report revealed that some single crystal SrO(LA$_{1-x}$ Sr$_{x}$MnO$_3$)$_{n}$ phase showed MR effect. In this study, layered perovskite SrO(LA$_{1-x}$ Sr$_{x}$MnO$_3$)$_2$ Phases were synthesized by solid state reaction at 140$0^{\circ}C$ in air atmosphere, for wide range of x and their phases were confirmed by X-ray diffraction. Electrical and magnetic properties were measured down to 10K and the possibility of MR effects was investigated.as investigated.

• Journal of the Mineralogical Society of Korea
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• v.16 no.2
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• pp.161-169
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• 2003

A phase transformation study on a synthetic amorphous diopside, $(Ca,Mg)SiO_3$has been carried out up to ∼30 GPa, and ∼$1000^{\circ}C$ using a diamond anvil cell and YAG laser heating system, respectively. A starting amorphous material shows a direct transition to cubic $(Ca,Mg)SiO_3$perovskite at high pressure, which contradicts to the crystalline diopside phase transformation sequence disproportionating into mixtures of the orthorhombic$ MgSiO_3$perovskite and the cubic $CaSiO_3$perovskite phases. This discrepancy might be due to the different starting materials as well as the temperature variations at each specific experiment performed. The present phase transfor mation sequence would modify the mineralogical assemblage in the Earth transition region and the lower mantle depending upon the pressure, temperature and the oxygen partial pressure.

• Journal of the Korean Ceramic Society
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• v.45 no.5
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• pp.290-296
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• 2008

$AB'_{0.5}B"_{0.5}O_3$ type complex perovskite structures which have been reported as proton conductors over $600^{\circ}C$ were studied. The $AB'_{0.5}B"_{0.5}O_3$ type complex perovskite structure is known to be more easily synthesized and has better stability than normal $ABO_3$ perovskite structure. And it is stable at about $800^{\circ}C$ in the $CO_2$ atmosphere, whereas the $BaCeO_3$ perovskite is easily decomposed into carbonate. In addition, this $AB'_{0.5}B"_{0.5}O_3$ type complex perovskite structure could simply produce oxygen vacancies within their structure not by introducing additional doping oxides but by just controling the molar ratio of $B'^{+3}$ and $B"^{+5}$ metal ions in the B site. Hence it is easy to design the structure which shows highly sensitive electrical conductivity to humidity. In this study, the single phase boundary of $BaR_{0.5+x}Ta_{0.5-x}O_{3-{\delta}}$(R = rare earth) complex perovskite structures and it's phase stability were investigated with changes in composition, x. And the humidity dependance of electrical conductivity at different $P_{H2O}$ conditions was investigated.

• Bulletin of the Korean Chemical Society
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• v.34 no.7
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• pp.2041-2043
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• 2013

A layered perovskite of Dion-Jacobson phase, $RbLaTa_2O_7$, was successfully exfoliated into colloidal suspension via successive ion-exchange and intercalation reaction. The pristine perovskite $RbLaTa_2O_7$ was synthesized by conventional solid-state reaction, and then, it was ion-exchanged with hydrochloric acid to obtain a protonic form of perovskite. The resulting proton-exchanged perovskite was reacted with ethylamine to increase interlayer spaces for further intercalation reaction. Finally, the ethylamine-intercalated form was exfoliated into nanosheets via an intercalation of bulky organic cations (tetrabutylammonium). According to X-ray diffraction (XRD) analysis, the TBA-intercalated form showed remarkably increased interlayer spacing (${\Delta}d$ = 1.67 nm) in comparison with that of the pristine material. Transmission electron microscopic image of exfoliated perovskite clearly revealed that the present exfoliated perovskite were composed of very thin layers. This exfoliated perovskite nanosheets could be applicable as building blocks for fabricating functional nanocomposites.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.427-427
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• 2016

Organic-inorganic hybrid perovskite have attracted significant attention as a new revolutionary light absorber for photovoltaic device due to its remarkable characteristics such as long charge diffusion lengths (100-1000nm), low recombination rate, and high extinction coefficient. Recently, power conversion efficiency of perovskite solar cell is above 20% that is approached to crystalline silicon solar cells. Planar heterojunction perovskite solar cells have simple device structure and can be fabricated low temperature process due to absence of mesoporous scaffold that should be annealed over 500 oC. However, in the planar structure, controlling perovskite film qualities such as crystallinity and coverage is important for high performances. Those controlling methods in one-step deposition have been reported such as adding additive, solvent-engineering, using anti-solvent, for pin-hole free perovskite layer to reduce shunting paths connecting between electron transport layer and hole transport layer. Here, we studied the effect of alkali metal halide to control the fabrication process of perovskite film. During the morphology determination step, alkali metal halides can affect film morphologies by intercalating with PbI2 layer and reducing $CH3NH3PbI3{\cdot}DMF$ intermediate phase resulting in needle shape morphology. As types of alkali metal ions, the diverse grain sizes of film were observed due to different crystallization rate depending on the size of alkali metal ions. The pin-hole free perovskite film was obtained with this method, and the resulting perovskite solar cells showed higher performance as > 10% of power conversion efficiency in large size perovskite solar cell as $5{\times}5cm$. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma optical emission spectrometry (ICP-OES) are analyzed to prove the mechanism of perovskite film formation with alkali metal halides.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.1
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• pp.64-69
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• 2019

Methylammonium lead triiodide ($MAPbI_3$)-based perovskite solar cells potentially have potential advantages such as high efficiency and low-cost manufacturing procedures. However, $MAPbI_3$ is structurally unstable and has low phase-change temperatures ($30^{\circ}C$ and $130^{\circ}C$); it is necessary to solve these problems. We investigated the crystal structure and phase separation using real-time temperature-change X-ray diffraction, transmission electron microscopy, and electron energy loss spectroscopy. $MAPbI_3$ has a tetragonal structure, and at about $35^{\circ}C$ the c-axis contracts, transforming $MAPbI_3$ into the related cubic crystal structure. In addition, at $130^{\circ}C$, phase separation occurs in which $CH_3NH_2$ and HI at the center of the unit cell of the perovskite structure are extracted by gas, leavingand only $PbI_2$ of the three-component structure, is produced as the final solid product.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.15 no.2
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• pp.86-91
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• 2005

The layered structure of organic-inorganic perovskite hybrids, $(C_nH_{2n+1}NH_3)_2CuC1_4$ (n = 6, 8, 10, 12) have synthesized. In $(C_nH_{2n+1}NH_3)_2CuC1_4$ compounds, the long-chain protonated alkylammonium ions as tilted bilayer type are inserted into perovskite-type layers of corner sharing $CuCl_6$ octahedron. Three solid phases have been characterized in the perovskite layered compound $(C_nH_{2n+1}NH_3)_2CuC1_4$ using HT-XRD and DSC. The $(C_nH_{2n+1}NH_3)_2CuC1_4$ compounds shows solid-solid phase transitions with stepwise increasing of the layer distance. Three different structures are explained by the conformational change of the long-chain protonated alkylammonium ions.