• Journal of the Korean Ceramic Society
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• v.29 no.6
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• pp.459-462
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• 1992

It has been reported that the size and characteristics of ferroelectric domains which have an essential role on the ferroelectric properties depend on the grain size of ferrolectric ceramics. Therefore understanding the change of domain characteristics with grain size is so important to know the dependence of dielectric constant, dielectric loss and aging on the grain size. In this research, the equilibrim domain with is calculated as d={{{{ SQRT { { 64 pi sigma a} over {3C11Ss2 } } }}. This calculated value is nearly same to the measured value of BaTiO3 and Pb(Zr0.4Ti0.6)O3 ceramics 90$^{\circ}$domain wall width. The calculated 90$^{\circ}$domain wall enerygy in Pb(Zr0.4Ti0.6)O3 which is obtained through the model is approximately 2$\times$10-2J/$m^2$.

• Journal of the Korean Ceramic Society
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• v.33 no.6
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• pp.672-678
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• 1996

The relationship between domain switching and acoustic emission (AE) during poling was investigated using the tetragonal ferroelectric ceramics with composition of (Pb,La)TiO3+0.01MnO2 The amount of AE generation during poling increased with increasing dc electric field and raising temperature. It was confirmed that the change of the amount of AE generation with poling condition resulted from the difference of the amount of 90$^{\circ}$ domain switching and total amount of AE generation for 10 minutes was approximately proportional to the amount of 90$^{\circ}$domain switching. The A generations of two specimens which have different tetragonality rations(c/s rations) 15 at% and 24at% La-doped were also investigated. The sample with c/a ratio of 1.012 where 90$^{\circ}$ domains are dominate had larger amount of AE generation and 90$^{\circ}$ domain switching compared with the sample with c/a ratio of 1.004 where 180$^{\circ}$ domains are dominant.

• Journal of the Korean Ceramic Society
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• v.34 no.5
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• pp.500-504
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• 1997

Perovskite Pb0.7Ba0.3Zn1/3Nb2/3O3 substituted with 0.3 mole fraction for Pb-site in PbZn1/3Nb2/3O3 relaxor and pyrochlore Pb1.83Ba0.29Zn1.71Nb2/3O6.39 were mixed and dielectric characteristics of this composites were investigated. Percolation limit of perovskite phase, which was determined by microstructural observation in the composite as an isolation of perovskite phase from pyrochlore matrix, was 28.9-47.5 vol%. Ferroelectric phase transition below percolation limit depends on a parameter which affects the propagation of lattice vibration between isolated perovskite phase and pyrochlore matrix. Therefore, it is believed that ferroelectric lattice vibration of isolated perovskite phase could be transfered to pyrochlore matrix when the oxygen octahedra are linked in 3-dimension and highly polarizable Pb2+ ions are contained in both phases.

• Journal of the Korean Ceramic Society
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• v.40 no.11
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• pp.1047-1057
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• 2003

A sub-nanometer resolution Scanning Nonlinear Dielectric Microscope (SNDM) was developed for observing ferroelectric polarization. We also demonstrate that the resolution of SNDM is higher than that of a conventional piezo-response imaging. Secondly, we report new SNDM technique detecting higher nonlinear dielectric constants $\varepsilon$$\_$3333/ and $\varepsilon$$\_$33333/. Higher order nonlinear dielectric imaging provides higher lateral and depth resolution. Finally, the formation of artificial small inverted domain is reported to demonstrate that SNDM system is very useful as a nano-domain engineering tool. The nano-size domain dots were successfully formed in LiTaO$_3$ single crystal. This means that we can obtain a very high density ferroelectric data storage with the density above 1T-bits/inch$^2$.

• Journal of the Korean Ceramic Society
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• v.43 no.11 s.294
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• pp.673-679
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• 2006

The discovery of ferroelectric barium titanate (BaTiO$_3$) in 1942 began the present era of dielectrics-based electronic ceramics. Ferroelectric barium titanate has a high dielectric constant and after the recognition of BaTiO$_3$ as a new ferroelectric compound, various attractive electrical properties have been extensively studied and reported. Since then, pioneering work on valence-compensated semiconduction led to the discovery of the positive temperature coefficient (PTC) of the resistance effect found in doped BaTiO$_3$. Significant progress has since followed with respect to understanding the PTC phenomena, advancing materials capabilities, and developing devices for sensor and switching applications. In this paper, the theoretical aspects of the various PTC models are discussed and the future trends of practical applications for PTC devices are briefly mentioned.

• Journal of the Korean Ceramic Society
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• v.54 no.3
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• pp.235-242
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• 2017

Changes in polarization and thermal expansion coefficients during temperature increase of a poled lead zirconate titanate (PZT) cube specimen switched by an electric field at room temperature are measured. The measured data are analyzed to construct governing differential equations for polarization and strain changes. By solving the differential equations, an experimental formula for the high temperature behavior of ferroelectric materials is obtained. It is found that the predictions by the formula are in good agreement with measures. From the viewpoint of macroscopic remnant state variables, it appears that the processes of electric field-induced switching at different temperatures are identical and independent of temperature between $20^{\circ}C$ and $110^{\circ}C$.

• Proceedings of the Korean Ceranic Society Conference
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• 2000.10a
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• pp.154.1-154
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• 2000

• Proceedings of the Korean Ceranic Society Conference
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• 2000.10a
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• pp.190.1-190
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• 2000

• ETRI Journal
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• v.33 no.1
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• pp.132-135
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• 2011

In this letter, we study the contemporary technologies for making ferroelectric films and the possibility of using the oscillator model of PZT-22 to analyze its ferroelectric properties. The material showed permittivity dispersion at 65 KHz and 88.5 KHz. We obtained relative attenuation ${\gamma}$, relaxation time ${\tau}$, and ${\varepsilon}_{max}$ of the material as 0.0008319, 0.5 s, and 603.438, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.12
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• pp.764-768
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• 2016

To investigate excess $Na^+$ effect, $Bi_{0.5}(Na_{0.78+x}K_{0.22})_{0.5}TiO_3$ ($0{\leq}x{\leq}0.05$) (BNKT) ceramics were prepared by using a conventional solid-state reaction method. The structure and ferroelectric properties of BNKT ceramics were characterized by XRD (X-ray diffraction) and polarization dependence by external electric field. Also, the temperature dependence of dielectric constant and loss were studied. From these results, it was found that appropriate excess $Na^+$ into BNKT ceramics compensate the volatility and induce dense ceramics. The enhanced piezoelectric coefficient (158 pC/N) and depolarization temperature ($202^{\circ}C$) were obtained for the x=0.01 composition.