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홍창효,강진규,조욱,이재신,Hong, Chang-Hyo,Kang, Jin-Kyu,Jo, Wook,Lee, Jae-Shin 한국전기전자재료학회 2016 전기전자재료학회논문지 Vol.29 No.6
We investigated the effect of $Bi_{1/2}(Na_{0.82}K_{0.18})_{1/2}TiO_3$ (BNKT) modification on the ferroelectric and electric-field-induced strain (EFIS) properties of lead-free $0.97Bi_{1/2}(Na_{0.82}K_{0.18})_{1/2}TiO_3-0.03LaFeO_3$ (BNKTLF) ceramics as a function of BNKT content (x= 0, 0.1, 0.2, 0.3, 0.5, and 1). BNKT-modified BNKTLF powders were synthesized using a conventional solid-state reaction method. As the BNKT content x increased from 0 to 1 the normalized electric-field-induced strain ($S_{max}/E_{max}$) was observed to increase at relatively low fields, i.e., below the poling field. Moreover, BNKTLF-30BNKT showed about 460 pm/V as low as at 3 kV/mm, which is a considerably high value among the lead-free systems reported so far. Consequently, it was confirmed that ceramic-ceramic composite, a mixture of an ergodic relaxor matrix and embedded ferroelectric seeds, is a salient way to make lead-free piezoelectrics practical with enhanced EFIS at low field as well as less hysterical.
Inversion boundary를 이용한 ZnO 바리스타 극성 제어
박종로(Jong-Lo Park),조욱(Wook Jo),박철재(Chul-Jae Park),전상윤(Sang-Yun Jeon),이종숙(Jong-Sook Lee),박찬(Chan Park) 대한전기학회 2009 대한전기학회 학술대회 논문집 Vol.2009 No.7
ZnO는 비선형 전류전압 특성으로 인해 급작스런 과전류 로부터 회로를 보호하는 바리스터로 널리 사용되고 있다. 이러한 바리 스터의 전기적 특성 및 미세조직을 제어하기 위하여 다양한 첨가물을 넣은 ZnO 바리스터의 미세구조에는 대부분의 입자에 wurtzite 구조의 결정학적 극성이 바뀌는 inversion boundary (IB)가 존재한다. ZnO의 비선형 전류전압 특성이 반도성의 ZnO 입자간 계면에 형성되는 쇼트키 장벽에 기인함을 감안할 때 계면의 결정화학적 특성에 영향을 주는 IB에 대한 이해는 필수적이다. 본 연구에서 IB가 ZnO 바리스터의 성능에 미치는 영향을 규명하기 위하여 ZnO-Bi₂O₃에 각각 Sb₂O₃ 또는 TiO₂를 첨가하여 결정학적 특성이 서로 상반되는 IB를 유도하였고, 첨가량을 조절하여 모든 입자가 IB를 가지도록 하였다. 화학 에칭을 한 시편의 SEM 관찰을 통해 입자의 형상, 크기, 분포 및 IB의 결정학적 특성 등을 분석하였다. 각 시편의 바리스터 특성은 임피던스의 온도 의존성과 상온에서의 전류-전압 특성을 통해 평가하였다. 관찰된 전기적 특성들을 입내 IB의 결정학적 구조와 이로부터 결과되는 입계면의 극성의 차이를 통해 해석하고자 한다.
조재현(Jae-Hyeon Cho),조욱(Wook Jo) 한국세라믹학회 2021 세라미스트 Vol.24 No.3
Magnetoelectric (ME) multiferroics manifesting the coexistence and the coupling of ferromagnetic and ferroelectric order are appealing widespread interest owing to their fascinating physical behaviors and possible novel applications. In this review, we highlight the progress in single-phase ME multiferroic oxides research in terms of the classification depending on the physical origins of ferroic properties and the corresponding examples for each case, i.e., material by material, along with their ME multiferroic properties including saturation magnetization, spontaneous polarization, (anti)ferromagnetic/ferroelectric transition temperature, and ME coefficient. The magnetoelectrically-active applications of high expectancy are presented by citing the representative examples such as magnetoelectric random-access-memory and multiferroic photovoltaics. Furthermore, we discuss how the development of ME multiferroic oxides should proceed by considering the current research status in terms of developed materials and designed applications. We believe that this short review will provide a basic introduction for the researchers new to this field.
조재현 ( Jae-hyeon Cho ),조욱 ( Wook Jo ) 한국전기전자재료학회 2022 전기전자재료학회논문지 Vol.35 No.3
분광학은 재료의 결정학적, 화학적 구조를 분석하기 위해 가장 보편적으로 활용되는 분석 기법이다. 이러한 기조에 따라 다양한 분석 소프트웨어와 peak fitting과 관련된 기술적 가이드라인이 보급되었지만, 정작 ‘왜’ 중간 계산 과정을 거치고 해당 함수를 쓰는지에 대한 논의는 부족한 실정이다. 따라서 본 tutorial에서는 X선 기반 분광광도계를 통해 얻은 데이터 분석의 기초를 논하고자 한다. 이를 위해 관련된 peak fitting을 위해 필요한 실용적 배경지식을 제시하였다. 나아가, 하나의 예시로 임의로 선정한 X선 광전자 분광법 데이터에 대한 curve fitting 과정을 순서에 따라 알기 쉽게 소개하였다. 제시한 기초 이론은 특정 소프트웨어에 국한된 내용이 아니라 fitting tool이 있는 모든 소프트웨어에서 그대로 활용 가능할뿐더러 다른 분광법 데이터를 분석하는 데 적용 가능하기 때문에, 본 내용을 숙지한다면 보다 수월한 연구 진행을 위한 바탕이 될 수 있을 것이라 기대한다. Spectroscopies are the most widely used for understanding the crystallographic, chemical, and physical aspects of materials; therefore, numerous commercial and non-commercial software have been introduced to help researchers better handling their spectroscopic data. However, not many researchers, especially early-stage ones, have a proper background knowledge on the choice of fitting functions and a technique for actual fitting, although the essence of such data analysis is peak fitting. In this regard, we present a practical guide for peak fitting for data analysis. We start with a basic-level theoretical background why and how a certain protocol for peak fitting works, followed by a step-by-step visualized demonstration how an actual fitting is performed. We expect that this contribution is sure to help many active researchers in the discipline of materials science better handle their spectroscopic data.
BaTiO₃ 기반의 적층 세라믹 캐피시터 (Multi-Layer Ceramic Capacitors)의 절연저항 열화 메커니즘과 신뢰성 분석 동향
이규탁(Ku-Tak Lee),천진성(Jinsung Chun),조욱(Wook Jo) 한국세라믹학회 2023 세라미스트 Vol.26 No.2
The demand for high performance multilayer ceramic capacitors (MLCCs) has rapidly increased keeping up with the recent trends in electronics seeking better performance per volume. It follows that thinning of dielectric layers of MLCC and atomization of powders have become two most challenging issues these days. However, it is well known that these two approaches are not free from reliability issues. In this brief review, we introduce the commonly accepted models that explain how dielectric materials fail during operation and how to evaluate the lifetime of MLCCs with a real world example.
화학양론 변화를 통한 리튬 이온 치환 니오브산 칼륨 세라믹의 이차상 제어 연구
여태수 ( Tae Soo Yeo ),이주현 ( Ju Hyeon Lee ),조욱 ( Wook Jo ) 한국전기전자재료학회 2024 전기전자재료학회논문지 Vol.37 No.5
In line with the development of electronic devices and technologies, the demand for improving ferroelectric materials’ performance is increasing. Since K<sub>0.5</sub>Na<sub>0.5</sub>NbO<sub>3</sub> (KNN), an eco-friendly ferroelectric material that does not use lead and has a high Curie temperature, it is attracting attention to its usability as a high-temperature dielectric, and various studies are being conducted to increase performance. In a KNN having a perovskite structure, there was a simulation result that the KNN has higher spontaneous polarization when the A-site in which sodium ions exist is replaced with lithium ions. If the simulation results can be proven experimentally, the application range of KNN-based ferroelectric materials will increase. To this end, we tried to manufacture a K<sub>1-x</sub>Li<sub>x</sub>NbO<sub>3</sub> (KLN) with high electrical characteristics by fabricating niobium-deficient and potassium-excessive compositions, which attempt was made to solve the stoichiometry problem by volatilization and suppress secondary phases. If KLN’s secondary phase suppression and relative permittivity improvement are successful, it will contribute to meeting the demand for developing electronic devices.
반대칭 교환 상호작용을 갖도록 Fe-Site가 제어된 PbFe<sub>1/2</sub>Nb<sub>1/2</sub>O<sub>3</sub>의 강유전/자기적 특성 연구
박지훈 ( Ji-hun Park ),이주현 ( Ju-hyeon Lee ),조재현 ( Jae-hyeon Cho ),장종문 ( Jong Moon Jang ),조욱 ( Wook Jo ) 한국전기전자재료학회 2022 전기전자재료학회논문지 Vol.35 No.3
We investigated the origin of magnetic behaviors induced by an asymmetric spin exchange interaction in Fe-site engineered lead iron niobate [Pb(Fe<sub>1/2</sub>Nb<sub>1/2</sub>)O<sub>3</sub>, PFN], which exhibits a room-temperature multiferroicity. The magnitude of spin exchange interaction was regulated by the introduced transition metals with a distinct Bohr magneton, i.e., Cr, Co, and Ni. All compositions were found to have a single-phase perovskite structure keeping their ferroelectric order except for Cr introduction. We discovered that the incorporation of each transition metal imposes a distinct magnetic behavior on the lead iron niobate system; antiferro-, hard ferro-, and soft ferromagnetism for Cr, Co, and Ni, respectively. This indicates that orbital occupancy and interatomic distance play key roles in the determination of magnetic behavior rather than the magnitude of the individual Bohr magneton. Further investigations are planned, such as X-ray absorption spectroscopy, to clarify the origin of magnetic properties in this system.
TSDC 방법을 이용한 AC 폴링된 PMN-PT 단결정의 디폴링 메커니즘 분석
이건주 ( Geon-ju Lee ),김황필 ( Hwang-pill Kim ),이상구 ( Sang-goo Lee ),이호용 ( Ho-yong Lee ),조욱 ( Wook Jo ) 한국센서학회 2020 센서학회지 Vol.29 No.1
Currently, increasing attention is being paid to relaxor-based ferroelectric single crystals in photoacoustic images, especially for highend applications. Among the crystals are (1-x)Pb(Mg<sub>1/3</sub>Nb<sub>2/3</sub>)O<sub>3</sub>-xPbTiO<sub>3</sub> (PMN-100xPT) single crystals located near their morphotropic phase boundary (x = 0.30-0.35) because of their ultrahigh piezoelectric and electromechanical coupling properties. The alternating current poling (ACP) treatment, rather than the conventional direct current poling treatment, has recently been spotlighted due to its effectiveness in enhancing the piezoelectric properties. So far, it has been suggested that the enhanced piezoelectricity originates from either a domain miniaturization to nanodomains or from an electric-field-induced monoclinic symmetry. In this study, we demonstrate by thermally stimulated depolarization current measurements that the effect of ACP is too complex to be explained using a single mechanism and that the proposed electric-field-induced monoclinic symmetry is unlikely to exist.