• 한국세라믹학회지
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• 제33권1호
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• pp.56-64
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• 1996

A large amount of papers about the cubic-to-tetragonal phase transition the ferroelectric domain structures of the BaTiO3 were already reported but there exist still some needs to observe the domain behaviors directly. In this study the domain structures of the tinned plates prepared from ta single crystal grown by the TSSG technique were observed using a polarizing microscope TE and X-ray topography. The spatial relation be-tween the orientation states of domains was investigated and the effects of external stresses and electric fields on the behaviors of ferroelectric and ferroelastic domains were studied. All the 90$^{\circ}$walls cut off in the crystal are the wedge shaped lamellar domains and all the straight boundaries in the observed domain patte군 can be interpreted as the head-to-tail 90$^{\circ}$walls. The irregular overlapped boundaries commonly observed by using a polarizing microscope and X-ray topography are complex combinations of well-known 90$^{\circ}$walls and are domain walls were predominant and were stabilized after surface polishing. In the paraelectric phase region the domain walls vanished but the residual surface strain patterns could be seen at the same positions of the stabilized 90$^{\circ}$a-a walls in the tetragonal phase region, These stabilized walls resulted from the surface strain had a memory effect in domain formation during the repeated phase transitions and could notr be affected by an external electtric field.

• 한국결정학회:학술대회논문집
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• 한국결정학회 2002년도 정기총회 및 추계학술연구발표회
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• pp.18-18
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• 2002

Although it was suggested in 1962 that an efficient wavelength conversion could be achieved using ferroelectric crystals of periodic 180° domains, it was not until 1990's that quasi-phase-matching (QPM) became realized, as technology for periodic poling of LiNbO₃ crystals was readily available. Since ferroelectric domain inversion brings about change of the sign of second-order nonlinear susceptibility, periodically poled ferroelectric structures provide an ideal way of achieving QPM for second-harmonic generation and optical parametric oscillation. Periodically poled ferroelectric domains can also be utilized for optical devices, such as Brags electrooptic modulators. fabrication of stable periodic domain structures depends on a number of poling parameters of a ferroelectric crystal, such as coercive field, internal field and electrical conductivity. We present poling kinetics of KNbO₃ crystals, which involve domain nucleation and growth, backswitching, relaxation of internal field. Optimum poling conditions were established by designing a proper wave shape of external field. We demonstrate an efficient second-harmonic generation using QPM in a periodically poled KNbO₃ crystal.

• 한국세라믹학회지
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• 제33권2호
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• pp.228-234
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• 1996

강유전성 BaTiO3의 분역 구조를 이해하는 것은 폴링과정에 있어서 대단히 중요하면 대부분의 BaTiO3 세라믹스에서 흔히 발견되는 구조 쌍정 계면에서의 배향관계는 아직까지 보고된 바 없다. 본 연구에서는 {111} 쌍정을 이루고 있는 길정시편을 이용하여 편광현미경하에서 분역구조를 관찰하고, 열처리에 의하여 상전이되는 동안 {111} 쌍정과 강유전성 분역의 거동을 현미경하에서 직접적으로 관찰하였다. {111} 쌍정면 암측으로 대칭적 분역구조가 발될되며, 그 배열 형태는 'V'자 모양과 수직하게 관통하는 것처럼 직선 모양의 두가지 형으로 분류된다. 열처리에 의하여 새로운 분역구조가 형성될때 {111} 쌍정면 주위에서는 대칭적 관계를 유지하면서 분역이 발달되며, 분역형성에 기인하는 표면변형도 {111} 쌍정에 대하여 항상 대칭적으로 발달된다. 이는 {111} 계면에서도 분극반향이 바뀌어지며 "머리-꼬리"의 전지적 안정성의 배향관계를 유지하는 것으로 설명할 수 있다.

• 한국세라믹학회지
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• 제29권6호
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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$.

• 한국세라믹학회지
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• 제33권6호
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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.

• 한국세라믹학회:학술대회논문집
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• 한국세라믹학회 2003년도 추계총회 및 연구발표회 초록집
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• pp.15-15
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• 2003

• 한국전기전자재료학회논문지
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• 제32권1호
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• pp.20-24
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• 2019

Ferroelectric material properties are strongly governed by domain structures and their evolution processes, but the evolution processes of complex domain patterns during a macroscopic electrical poling process are still elusive. In the present work, domain-evolution processes in a PZT ceramic near the morphotropic phase-boundary composition were studied during a step-wise electrical poling using piezoresponse force microscopy (PFM). Electron backscatter diffraction was used with the PFM data to identify the grain boundaries in the region of interest. In response to an externally the applied electric field, growth and retreat of non-$180^{\circ}$ domain boundaries wasere observed. The results indicate that ferroelectric polarization-switching nucleates and evolves in concordance with the pattern of the pre-existing domains.

• 한국세라믹학회지
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• 제40권11호
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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 Physical Society
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• 제73권10호
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• pp.1561-1565
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• 2018

The dielectric properties of the uniaxial relaxor ferroelectric $Sr_xBa_{1-x}Nb_2O_6$ with x = 0.75 were investigated along the polar [001] direction as a function of temperature. The capacitance maximum showed the frequency dispersion commonly observed in relaxors. Additional weak dielectric anomalies were observed in the paraelectric phase; they were only seen during the heating process and disappeared upon subsequent cooling. These were attributed to the existence of large polar clusters strongly pinned at defects and/or to random fields and their metastable characters. Aligning the ferroelectric domains along the polar axis at room temperature removed the high-temperature dielectric anomalies. The dependences of the capacitance and the dielectric maximum temperature on the magnitude of the poling field were investigated.

• 한국전기전자재료학회논문지
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• 제18권11호
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• pp.983-989
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• 2005

[ $PZT(Pb(Zr,Ti)O_3)$ ] thin films were deposited by multi-target reactive sputtering method on $RuO_2$ substrates. Pure perovskite phase PZT films could be obtained by introducing Ti-oxide seed layer on the $RuO_2$ substrates prior to PZT film deposition. The PZT films deposited on the $RuO_2$ substrates showed highly voltage-shifted hysteresis loop compared with the films deposited on the Pt substrates. The surface of $RuO_2$ substrate was found to be reduced to metallic Ru in vacuum at elevated temperature, which caused the formation of oxygen vacancies at the initial stage of PZT film deposition and gave rise to the voltage shift in the P-E hysteresis loop of the PZT capacitor. The fatigue characteristics of the PZT capacitors under unipolar wane electric field were different from those under bipolar wane. The fatigue test under unipolar wane showed the increase of polarization. It was thought that the ferroelectric domains which had been pinned by charged defects such as oxygen vacancies and the charged defects were reduced in number by combining with the electrons injected from the electrode under unipolar wave, resulting in the relaxation of the ferroelectric domains and the increase of polarization.