Investigation of crystal structure and magnetic properties in Zn doped Bi0.84La0.16FeO3 ceramics at morphotropic phase boundary

Tho, P.T.,Dang, N.V.,Nghia, N.X.,Khiem, L.H.,Xuan, C.T.A.,Kim, H.S.,Lee, B.W. Elsevier 2018 The Journal of physics and chemistry of solids Vol.121 No.-

<P><B>Abstract</B></P> <P>In this investigation, we have studied the crystal structure and magnetic properties of Zn doped Bi0.84La0.16FeO3 (<I>x</I> = 0.02–0.1) ceramics at the morphotropic phase boundary of rhombohedral and orthorhombic phases. Rietveld refinement of the obtained XRD patterns and Raman spectroscopy confirm the presence of multiphases crystal structure of <I>R3c</I> rhombohedral and <I>Pbam</I> orthorhombic. Room temperature magnetic measurements showed weak ferromagnetic ordering and enhancement in magnetization and coercivity with dominating of orthorhombic phase. The isothermal structural transition from <I>R3c</I> to <I>Pbam</I> is caused for the decrease in magnetization and the increase in coercivity.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The crystal structure of Bi<SUB>0.84</SUB>La<SUB>0.16</SUB>Fe<SUB>1-x</SUB>Zn<SUB>x</SUB>O<SUB>3</SUB> at the morphotropic phase boundary. </LI> <LI> The microstructure reveals the coexistence crystal phase and their phase boundary. </LI> <LI> The isothermal structural transition induces the change in magnetic properties. </LI> <LI> The vertical shift (exchange bias) is observed in compounds. </LI> </UL> </P>

Atomic Migration Induced Crystal Structure Transformation and Core-Centered Phase Transition in Single Crystal Ge₂Sb₂Te₅ Nanowires

Lee, Jun-Young,Kim, Jeong-Hyeon,Jeon, Deok-Jin,Han, Jaehyun,Yeo, Jong-Souk American Chemical Society 2016 NANO LETTERS Vol.16 No.10

<P>A phase ichange nanowire holds a promise for nonvolatile memory applications, but its transition mechanism has remained unclear due to the analytical difficulties at atomic resolution. Here we obtain a deeper understanding on the phase transition of a single crystalline Ge2Sb2Te5 nanowire (GST NW) using atomic scale imaging, diffraction, and chemical analysis. Our cross-sectional analysis has shown that the as-grown hexagonal close-packed structure of the single crystal GST NW transforms to a metastable face-centered cubic-structure due to the atomic migration to the pre-existing vacancy layers in the hcp structure going through iterative electrical switching. We call this crystal structure transformation 'metastabilization', which is also confirmed by the increase of set-resistance during the switching operation. For the set to-reset transition between, crystalline and amorphous phases, high-resolution imaging indicates that the longitudinal center of the nanowire: mainly undergoes phase transition. According to the atomic scale analysis of the GST NW after repeated electrical switching, partial crystallites are distributed around the core-centered amorphous region of the nanowire where atomic migration is mainly induced, thus pote-ptially leading to low power electrical switching. These results provide a novel understanding of phase change nanowires, and can be applied to enhance the design of nanowire phase change memory devices for improved electrical-performance.</P>

PL 판정을 위한 3상 몰드변압기의 소손 패턴 분석

최충석 한국화재감식학회 2012 한국화재감식학회 학회지 Vol.3 No.1

The purpose of this study is to compare the characteristics of transformers according to their types and to analyze, and investigate the cause of, the failure patterns of 3 phase mold transformers collected from places where accidents have occurred. Since a mold transformer is small in size compared to a general transformer, it can easily be installed in a receiving substation. However, in the case of a mold transformer, it is difficult to diagnose its heat radiation and abnormal phenomenon during system operation. From the 3 phase mold transformer to which failure has occurred, a trace of carbonization was found between the U-phase and V-phase, and a trace of crack was found at some part of the secondary side of the U-phase. The metal structure of the copper cable used as electric cable is amorphous and has no direction and crystallinity. However, it was found from the metal structure of the bus bar (copper) of the damaged 3 phase mold transformers that crystalline arrays unique to copper cables disappeared and a new shape of crystal structure was formed. It can be seen that the copper particles had comparatively homogeneous voids and that their size was enlarged. In addition, it was found that the voids and crystal particles were bigger at the surface of the conductor than at the center.

Crystal Structure Transformation and Dielectric Properties of Polymer Composites Incorporating Zinc Oxide Nanorods

Jinhong Yu,Wei Wu,Dan Dai,Yingze Song,Chaoyang Li,Nan Jiang 한국고분자학회 2014 Macromolecular Research Vol.22 No.1

Zinc oxide (ZnO) nanorods were synthesized using a modified wet chemical method. Poly(vinylidene fluoride-co-hexafluoropropylene), P(VDF-HFP), nanocomposites with different ZnO nanorods loadings were prepared viaa solution blend route. Field emission scanning electron microscopic (FE-SEM), X-ray diffraction (XRD), Fouriertransform infrared spectroscopy (FTIR) were used to investigate the structure and morphology of the nanocomposites. XRD and FTIR data indicate that the incorporation of ZnO nanorods promote the crystalline structure transformationof P(VDF-HFP). As the content of ZnO nanorods increases, the β phase structure increases while the α phasedecreases. In addition, the dielectric properties of the P(VDF-HFP) and its composites were systematically studied.

전기장에 놓인 네마틱 액정 방울의 CARS 현미경 관찰

박진순,김종현,이은성,박주현,Satoshi Kawata 한국물리학회 2013 새물리 Vol.63 No.4

We stereoscopically observed the response of liquid crystal droplets in an electric filed by using a coherent anti-stokes Raman scattering microscope and polarizing optical microscope. In silicon oil, a nematic liquid crystal can exist as droplets. The directors orient radially and induce a point defect in the center. When an electric field is applied, the directors tend to align along the field's directions, and the point defect changes into a line disclination. Even more, the shape of the spherical droplets changes oval with increasing field strength in the low-frequency range. The movement of the ions in a liquid crystal seems to induce a shape change. Coherent anti-stokes Raman scattering (CARS) 현미경과편광광학현미경을 이용하여 액정 방울이 전기장에서 나타내는 액정의배향 구조와 변화 과정을 입체적으로 관찰하고 이해하였다.실리콘오일에서 네마틱 액정은 마이크로미터 크기의 방울로 존재할 수 있다. 액정 방울을 이루는 방향자는 계면에서 면에 수직하게 늘어선다. 그리고중심에 점결함을 형성한다. 전기장을 인가하면방향자는 전기장 방향으로돌아가려한다. 전기장이 증가함에 따라 방울 가운데 있던 점결함이방울과 오일의 경계 부분으로 이동하는 것처럼 보이고 선결함인디스클리네이션으로 변화한다. 전기장의 주파수가 낮으면 방향자 뿐만아니라 액정 방울의 모양이 변화한다. 전기장 방향으로 길이가 늘어난다. 주파수가 낮을수록 그 변화폭이 크다. 액정 내에 포함되어 있는 이온에의한 영향이라고 생각된다.

어닐링 열처리 조건에 따른 NITINOL 형상기억합금의 상변환 특성 연구

윤성호 ( Sung Ho Yoon ),여동진 ( Dong Jin Yeo ) 한국복합재료학회 2005 Composites research Vol.18 No.2

Effect of Radio-Frequency Electric Power Applied to a Boron Nitride Unbalanced Magnetron Sputter Target on the Deposition of Cubic Boron Nitride Thin Film

Ji-Sun Ko,Jong-Keuk Park,Wook Seong Lee,허주열,Young Joon Baik 대한금속·재료학회 2013 METALS AND MATERIALS International Vol.19 No.6

Cubic boron nitride (c-BN) films were deposited by an unbalanced magnetron sputtering method. A (100) Si wafer with a nanocrystalline diamond thin film as a surface coating layer or that without it was used as a substrate. The target power was varied from 100 to 400 W. A boron nitride target was used, which was connected to a radio frequency power supply. High frequency power connected to a substrate holder was used for self-biasing. The deposition pressure was 0.27 MPa with a flow of Ar (18 sccm) - N2 (2 sccm) mixed gas. The existence of threshold bias voltages for c-BN formation and resputtering were observed irrespective of target power. The bias voltage window for c-BN formation broadened with increased target power. The deposition rate decreased with enhanced bias voltage and decreased target power. Residual stresses of the films did not vary noticeably with target power within the target power range of c-BN formation. A parameter space for c-BN formation according to the target power and the bias voltage, as two variables, was suggested.

De-twinning 과정에 따른 선택적 정방정계 결정구조 형성과 마이크로 스케일 형상기억합금의 pseudo-plastic 거동에 대한 연구

송지환(Jihwan Song),김동철(Dongchoul Kim) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11