• 한국세라믹학회지
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• 제25권6호
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• pp.694-698
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• 1988

Pb(Zr, Ti)O3-Pb(Co, Nb)O3 systems were investigated by x-ray diffraction method. System contains rhombohedral, tetragonal, and pseudocubic structures at room temperature. Crystal symmetry was changed from 4-fold symmetry to 3-fold symmetry by substituting Pb(Co1/3, Nb2/3)O3 ; PCN, to Pb(Zr0.52, Ti0.48)O3 ; PZT. As the substituted PCN concentration was increased, an increase in a-axis direction and a decrease in c-axis in the perovskite structure were occurred simultaneously, so that the crystal symmetry was changed into such way. In the higher sinteringtemperatures, the unit cell distortions occurred rather in the lower substitution range of PCN. The ferroelectric properties were maximized at the region that tetragonal and rhombohedral or pseudocubic structures were coexist.

• 한국자기공명학회논문지
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• 제19권1호
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• pp.29-35
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• 2015

The microscopic dynamics of $CsH_2PO_4$, with two distinct hydrogen bond lengths, are studied by static nuclear magnetic resonance (NMR) and magic angle spinning (MAS) NMR. The proton dynamics of the two crystallographically inequivalent hydrogen sites were discussed in terms of the $^1H$ NMR and $^1H$ MAS NMR spectra. Although the hydrogen bonds have two inequivalent sites, H(1) and H(2), distinct proton dynamics for the two sites were not found. Further, the $^{133}Cs$ spectrum is more or less continuous near $T_{C1}$ (=153 K). Finally, the phase transition mechanism of $T_{C1}$ in $CsH_2PO_4$ is related to the ordering of protons.

• E2M - 전기 전자와 첨단 소재
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• 제9권8호
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• pp.836-850
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• 1996

In this study, we have analyzed structural analysis and measured ferroelectric characteristics of PZT thin films prepared by sol gel process with different sintering conditions and different Zr/Ti mot%. When the Zr mot% of PZT thin film was increased, it was found that the remanent. polarization and coercive field were decreased and increased, respectively. Also, the maxium dielectric constant of PZT(50/50) thin film was 786.8. We got double hysteresis(anti-fcrroelectric) curve from PbZrO$_{3}$ thin film. As heating rate goes up, pyrochlore phase of PZT thin film was decreased and dielectric and ferroelectric characteristics were improved. As a result of variation of sintering temperature and time 500.deg. C-800.deg. C and 5 sec.-8 hours, respectively, we got optimal sintering temperature and time. The optimium sintering temperature and time of conventional furnace method and rapid thermal processing method were 650.deg. C-700.deg. C for 30-60 minutes and 700.deg. C/20 seconds-2 minutes, respectively.

• 한국표면공학회지
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• 제50권4호
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• pp.277-281
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• 2017

Ferroelectric ceramics are broadly used for various industrial applications. In this research, the lead-free ferroelectric ceramics of $(K_{0.5}Na_{0.5})NbO_3$ was fabricated by using the solid state synthesis. The $(K_{0.5}Na_{0.5})NbO_3$ pellets were sintered at 1200, 1150 and $1100^{\circ}C$ for 4 hours in air atmosphere. Field-emission scanning electron microscopy (FE-SEM) characterization of the sintered KNN ceramics revealed surface morphology and grain size. And we used the X-ray diffraction (XRD) for measuring the sample crystal phase. Temperature dependence of the dielectric constant was measured by using an LCR meter. The sintered at $1150^{\circ}C$ for 4 hours sample has a highest dielectric constant 6011 at Curie temperature ($T_C$) and dense structure with $2.33{\mu}m$ grain size.

• 한국세라믹학회지
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• 제42권11호
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• pp.763-769
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• 2005

Ferroelectric $ReMnO_3$(Re:Ho, Er) thin films were deposited on Si(100) substrate by Metal-Organic Chemical Vapor Deposition (MOCVD). Crystallinity and electric properties of $ReMnO_3$(Re:Ho, Er) thin films were investigated as a function of thermal heat treatment process, CHP (Conventional Heat-treatment Process) and RTP (Rapid Thermal Process). $ReMnO_3$(Re:Ho, Er) thin films prepared by RTP showed higher c-axis preferred orientation and homogeneous surface roughness than those prepared by CHP. The remnant polarization of ferroelectric hysteresis loop of $ReMnO_3$(Re:Ho, Er) thin films was strongly dependent on the c­axis preferred orientation of hexagonal single phase, and the leakage current characteristics of thin films were dependent on the homogeneity of grain size as well as surface roughness of thin films.

• 한국전기전자재료학회논문지
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• 제15권9호
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• pp.764-769
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• 2002

The effect of excess Bi contents on the ferroelectric properties of B $i_{3.25}$ L $a_{0.75}$ $Ti_3$ $O_{12}$ (BLT) thin films has been investigated. Bismuth lanthanum titanate thin films with excess Bi contents were prepared onto Pt/Ti/ $SiO_2$/Si substrate by metalorganic decomposition (MOD) technique. The structure and morphology of the films were analyzed using X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. From the XRD analysis, BLT thin films show polycrystalline structure and the layered-perovskite phase was obtained over 10% excess of Bi contents. As a result of ferroelectric characteristics related to the Bi content of the BLT thin film, the remanent polarization and dielectric constant decreased with increasing over Bi content of 10% excess. The BLT film with Bi content of 10% excess was measured to have a dielectric constant of 326 and dielectric loss of 0.024. The BLT thin films showed little polarization fatigue test up to 3.5$\times$10$^{9}$ bipolar switching cycling.

• 한국전기전자재료학회논문지
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• 제34권5호
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• pp.386-392
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• 2021

Multiferroics exhibiting the coexistence and a possible coupling of ferromagnetic and ferroelectric order are attracting widespread interest in terms of academic interests and possible applications. However, room-temperature single-phase multiferroics with soft ferromagnetic and displacive ferroelectric properties are still rare owing to the contradiction in the origin of ferromagnetism and ferroelectricity. In this study, we demonstrated that sizable ferromagnetic properties are induced in the ferroelectric bismuth ferrite-barium titanate system simply by introducing Co ions into the A-site. It is noted that all modified compositions exhibit well-saturated magnetic hysteresis loops at room temperature. Especially, 70Bi_0.95Co_0.05FeO₃-30Ba_0.95Co_0.05TiO₃ manifests noticeable ferroelectric and ferromagnetic properties; the spontaneous polarization and the saturation magnetization are 42 µC/cm² and 3.6 emu/g, respectively. We expect that our methodology will be widely used in the development of perovskite-structured multiferroic oxides.

• 한국재료학회:학술대회논문집
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• 한국재료학회 1995년도 추계 학술발표 강연 및 논문개요집
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• pp.80-80
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• 1995

• 한국재료학회:학술대회논문집
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• 한국재료학회 1993년도 추계 학술발표 강연 및 논문 개요집
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• pp.105-105
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• 1993

• 한국재료학회지
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• 제22권7호
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• pp.342-345
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• 2012

The dielectric properties and phase transformation of poled <001>-oriented $Pb(Mg_{1/3}Nb_{2/3})O_3-x%PbTiO_3$(PMN-x%PT) single crystals with compositions of x = 20, 30, and 35 mole% are investigated for orientations both parallel and perpendicular to the [001] poling direction. An electric-field-induced monoclinic phase was observed for the initial poled PMN-30PT and PMN-35PT samples by means of high-resolution synchrotron x-ray diffraction. The monoclinic phase appears from $-25^{\circ}C$ to $100^{\circ}C$ and from $-25^{\circ}C$ to $80^{\circ}C$ for the PMN-30PT and PMN-35PT samples, respectively. The dielectric constant (${\varepsilon}$)-temperature (T) characteristics above the Curie temperature were found to be described by the equation$(1/{\varepsilon}-1/{\varepsilon}_m)^{1/n}=(T-T_m)/C$, where ${\varepsilon}_m$ is the maximum dielectric constant and $T_m$ is the temperature giving ${\varepsilon}_m$, and n and C are constants that change with the composition. The value of n was found to be 1.82 and 1.38 for 20PT and 35PT, respectively. The results of mesh scans and the temperature-dependence of the dielectric constant demonstrate that the initial monoclinic phase changes to a single domain tetragonal phase and a to paraelectric cubic phase. In the ferroelectric tetragonal phase with a single domain state, the dielectric constant measured perpendicular to the poling direction was dramatically higher than that measured in the parallel direction. A large dielectric constant implies easier polarization rotation away from the polar axis. This enhancement is believed to be related to dielectric softening close to the morphotropic phase boundary.