• 한국세라믹학회지
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• 제31권8호
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• pp.841-848
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• 1994

The sintering behavior of La-modified PbTiO3 ceramics was investigated in order to improve the poor sinterability of PbTiO3. Addition of La improved the sinterability. It was confirmed that this improvement was due to the decrease in tetragonality ratio c/a of crystal lattice. The variations of dielectric constant and pyroelectric coefficient were measured with temperature. It was observed that with the increase of La content, Curie temperature decreased and dielectric constant at room temperature increased. La-modified PbTiO3 ceramics had smaller pyroelectric figure of merits than those of pyroelectric materials in use. The effects of grain size on dielectric and pyroelectric properties were also investigated. The change of grain size had effect on maximum dielectric constant and pyroelectric coefficient, but is had little effect on pyroelectric figure of merit at room temperature. The closer examination near ferro-paraelectric phase transition temperature revealed that the behavior of phase transition approached a more relaxor character with the increase of La content and the decrease of grain size.

• 한국진공학회지
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• 제6권S1호
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• pp.141-153
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• 1997

The paraelectric cubic-to-ferroelectric tetragonal phase transition of the thin Pb(Zr, Ti)$O_3$ (PZT) films grown on MgO(001) substrate was investigated in a series of synchrotron x-ray scattering experiments. As the thickness of the film decreases the transition temperature and the amount of the tetragonal distortion were decreased continuously Different from only the c-domains were existent in the thinnest 25nm thick film. Based on this we propose a model for the domain structure of the tetragonal PZT/MgO(100) film that is very different from the ones suggested in literature. We attribute the suppression of the transition to the substrate field that prefers the c-type domains near the interface and suppresses the tetragonal distortion to minimize the film-substrate lattice mismatch.

• 한국자기공명학회논문지
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• 제17권1호
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• pp.19-23
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• 2013

The temperature dependences of the NMR spectrum and the spin-lattice relaxation times in $KH_2PO_4$ were investigated via single-crystal NMR and MAS NMR. The stretched-exponential relaxation that occurred because of the distribution of correlation times was indicative of the degree of the distribution of the double-well potential on the hydrogen bond. The behaviors responsible for the strong temperature dependences of the $^1H$ and $^{31}P$ spin-lattice relaxation times in the rotating frame $T_{1{\rho}}$ in $KH_2PO_4$ are likely related to the reorientational motion of the hydrogen-bond geometry and the $PO_4$ tetrahedral distortion.

• 전기의세계
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• 제28권5호
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• pp.39-43
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• 1979

The aging of permittivity of a barium titanate dielectrics doped with La$_{2}$O$_{3}$ under zero and low DC field has been studied. The aging rate was decreased as the amount of La$_{2}$O$_{3}$ addition is increased to 3 mole%. The zero field aging rate of barium titahate doped with La$_{2}$O$_{3}$. 3TiO$_{2}$ was similar to that doped with La$_{2}$O$_{3}$.5V/mil DC field aging rate of La$_{2}$O$_{3}$.3TiO$_{2}$ doped sample, howeve, was lowered to that of La$_{2}$O$_{3}$ doped sample. When the phase transformation is occured from the paraelectric state to the ferroelectric state, 90.deg. domains are mucleated in order that the system becomes thermodynamically more stable. It is concluded that the aging phenomenon is occured as the dielectric constant is decreasing by the nucleation and growth of 90.deg. domains.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1997년도 춘계학술대회 논문집
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• pp.217-221
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• 1997

We have investigated the ferroelectric properties of multi-layered SrBi$_2$Ta$_2$$O_{9}$Pb(Zr,Ti)O$_3$, SBT/PZT, thin film capacitors. Specimens were prepared onto Pt-coated Si wafer by sol-gel method. Ferroelectric properties of these finns could be obtained only for thin SBT layers below 50nm in thickness. The values of dielectric constant and remnant polarization depend mainly on the thickness of SBT layer, which arises from the paraelectric interface layer between SBT and PZT due to the thermal diffusion of Pb. The value of remnant poarization of PZT/SBT is greater than that of SBT, and the plarization fatigue behaviors of PZT/SBT/Pt capacitors are somewhat improved as compared with those of PZT/Pt.t.

• Journal of Korean Vacuum Science & Technology
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• 제3권2호
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• pp.130-133
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• 1999

Paraelectric ZrTiO4 thin films were synthesized on a Si(100) substrate using DC magnetron reactive sputtering. Films deposited above-400$^{\circ}C$ exhibited crystalline characteristics. The dielectric constants ($\varepsilon$) and dielectric losses (tan$\delta$) of as-deposited and annealed films were measured in the 1 MHz range using a Pt upper electrode and a phosphorous-doped si bottom electrode. Preliminary data showed that as the deposition temperature increased, the dielectric losses decreased while the dielectric constants did not change significantly. similar trends for dielectric losses were observed when the as-deposited samples were annealed at 800$^{\circ}C$. The reduction of dielectric losses at high-deposition temperatures and post annealing correlated well with the x-ray diffraction peak widths.

• 한국세라믹학회지
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• 제35권5호
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• pp.512-520
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• 1998

PLZT(7.5/70/30) was initially a cubic phase having diffuse phase transition at high temperatures. Sn-sub-stitution for PLZT(7.5/70/30) underwent an irreversible phase transition from cubic to rhom-bohedral structure. However PLZTS(7.5/70/30/y=5 & 10) could be reversibly switched from paraelectric to ferroelectric phase under electric field without showing a significant change in crystal structure. With in-creasing the amount of Sn-substitution the P-E behaviors of the PLZTS became more antiferroelectric which was similar to the effect of La-substitution of PLZT. Our study may suggest that Sn-substitution ef-fectively weakens a formation of long-range order between polar Ti-or Zr- containing octahedra which greatly affects strain properties.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1997년도 추계학술대회 논문집
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• pp.48-51
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• 1997

(Pb. La)TiO$_3$ thin films were fabricated by sol-gel Processing and spin-coated on the Pt substrate. The spin-coated PLT films were sintered at 75$0^{\circ}C$ for 5min by rapid thermal ann La content dependence of the electrical properties of the PLT thin films are discussed. Wit La mole% from 20 to 36mo1e%. the dielectric constant of the PLT thin films decreased f 570. P-E hysteresis loops changed from ferroelectric to paraelectric. and the charge storage charging time decreased. The Curie Point decreased with increasing La content. The leak density also decreased and La 36mo1% species shows mood characteristics less than 10- electric field 500 (KV/cm) Because of the broad range of composition-controlled ferroelectric PLT thin films are suitable for memory application.

• Transactions on Electrical and Electronic Materials
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• 제17권1호
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• pp.29-32
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• 2016

Using the various exchange-correlation functionals, such as LDA, GGA-PBE, GGA-PBEsol and GGA-AM05 functionals, first principle studies were conducted to determine the structures of paraelectric and ferroelectric PbTiO₃. Based on the structures determined by the various functionals, the piezoelectric properties of PbTiO₃ are predicted under the density-functional perturbation theory (DFPT). The present prediction with the various GGA functionals are closer to the experimental findings compared to the LDA values. The present DFT calculations using the GGA-PBEsol functional estimate the experimental data more reasonably than the conventional LDA and GGA fucntionals. The GGA-AM05 functional also predicts the experimental data as well as the GGA-PBEsol. The piezoelectric tensor calculated with PBEsol is relatively insensitive to pressure.

• 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.