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BaO 과잉량에 따른 BaTiO<sub>3</sub>의 전기전도도
여홍구,국민호,김명호,송태권,배동식,박태곤,이순일,Yeo, Hong-Goo,Kuk, Min-Ho,Kim, Myong-Ho,Song, Tae-Kwon,Bae, Dong-Sik,Park, Tne-Gone,Lee, Soon-Il,Randall, Clive A. 한국세라믹학회 2005 한국세라믹학회지 Vol.42 No.5
In this study the electrical conductivity of excess BaO in $BaTiO_3$ was measured to investigate the relationship between defects and solubility in the temperature range of $900^{\circ}C$ to $1300^{\circ}C$ under various oxygen partial pressure. First of all, quenched $BaTiO_3$ powders of various Ba/Ti ratios were analysed by X-ray diffraction to confirm whether second phase is formed or not. As the results, we observed the solubility of BaO in the temperature range of $1200^{\circ}C$ to $1400^{\circ}C$, and it was also found that the conductivity minima move to lower $PO_2$ with increasing excess BaO within solubility limit.
비납계 Bi<sub>0.5</sub>Na<sub>0.5</sub>의 강유전 및 압전 특성에 미치는 Nb-doping 효과
여홍구,성연수,송태권,조종호,정순종,송재성,김명호,Yeo, Hong-Goo,Sung, Yeon-Soo,Song, Tae-Kwon,Cho, Jong-Ho,Jeong, Soon-Jong,Song, Jae-Sung,Kim, Myong-Ho 한국재료학회 2006 한국재료학회지 Vol.16 No.11
Nb was doped to Pb-free $(Bi_{0.5}Na_{0.5})TiO_3$ (BNT) by a solid state mixing process to form $(Bi_{0.5}Na_{0.5})Ti_{1-x}Nb_xO_3\;(x=0{\sim}0.05)$ (BNTNb) and its doping effects on ferroelectric and piezoelctric properties of BNT were investigated. The BNTNb solid solutions were formed up to x=0.01 with no apparent second phases while grain sizes decreased. As x increased, coercive field ($E_c$) and mechanical quality factor ($Q_m$) decreased but piezoelectric constant ($d_{33}$) increased, which indicates Nb acts as a donor for BNT.
단일상 자기-전기 다강체 박막 및 공정에 대한 연구동향
여홍구(Hong Goo Yeo) 한국세라믹학회 2021 세라미스트 Vol.24 No.3
Advance in the growth and characterization of multiferroic thin film promises new device application such as next generation memory, nanoelectronics and energy harvesting. In this review, we provide a brief overview of recent progress in the growth, characterization and understanding of thin-film multiferroics. Driven by the development of thin film growth techniques, the ability to produce high quality multiferroic thin films offers researchers access to new phase and understanding of these materials. We discuss that epitaxial strain and atomic-level engineering of chemistry determine the muliferroic thin film properties. We then discuss the new structures and properties of non-equilibrium phases which is stabilized by strain engineering.
비납계 (Bi<sub>0.5</sub>Na<sub>0.5</sub>)<sub>(1-x)</sub>Ba<sub>x</sub>TiO<sub>3</sub> 압전 세라믹 재료의 최적 조성
성연수,여홍구,조종호,송태권,정순종,송재성,김명호,Sung, Yeon-Soo,Yeo, Hong-Goo,Cho, Jong-Ho,Song, Tae-Kwon,Jeong, Soon-Jong,Song, Jae-Sung,Kim, Myong-Ho 한국재료학회 2007 한국재료학회지 Vol.17 No.2
Optimum compositions for piezoelectric properties of $(Bi_{0.5}Na_{0.5})_{(1-x)}Ba_xTiO_3$ ceramics were investigated in the range of $x=0{\sim}0.1$ covering rhombohedral to tetragonal phase regions. No impurity phases other than a perovskite phase were found and the grain size decreased with increasing x. A two-phase coexisting morphotropic phase area rather than boundary dividing rhombohedral and tetragonal phase regions appeared to exist at $x=0.05{\sim}0.08$. As for piezoelectric properties within morphotropic phase compositions, the piezoelectric constant ($d_{33}$) and the electromechanical coupling factor ($K_p$) showed peak values at x=0.065, 192 pC/N and 34%, respectively, indicating x=0.065 as an optimum composition for piezoelectric $(Bi_{0.5}Na_{0.5})_{(1-x)}Ba_xTiO_3$ ceramics.
류시완,여홍구 국립7개대학공동논문집간행위원회 2004 공업기술연구 Vol.4 No.-
Spur-dike is the structure, installed at the river side, controlling the velocity and direction of the flow and protecting the bank erosion. caused by the flow. For this, the determination of the distances and spaces between the spur-dikes and the direction against the flow are most important. The objective of this study is to investigate the flow characteristics between the spur-dikes and suggest the optimal design parameters of Spur-dike. From this study, it is found that the distance between structures controls the scale and strength of the eddies between each pair of spur-dikes and the angle against the flow also affects the performance of series of spur-dikes.