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Choi, Hyunkyung,Kim, Hyung Joon,Shim, In-Bo,Lee, In Kyu,Kim, Chul Sung Elsevier 2017 Materials research bulletin Vol.93 No.-
<P><B>Abstract</B></P> <P>LiFe<SUB>1/3</SUB>Co<SUB>1/3</SUB>Ni<SUB>1/3</SUB>PO<SUB>4</SUB> and its fully deintercalated Fe<SUB>1/3</SUB>Co<SUB>1/3</SUB>Ni<SUB>1/3</SUB>PO<SUB>4</SUB> compounds were prepared by the vacuum-sealed solid state reaction method, and chemical-oxidation process with reaction of LiFe<SUB>1/3</SUB>Co<SUB>1/3</SUB>Ni<SUB>1/3</SUB>PO<SUB>4</SUB> and No<SUB>2</SUB>BF<SUB>4</SUB> in acetonitrile. The crystal structure of LiFe<SUB>1/3</SUB>Co<SUB>1/3</SUB>Ni<SUB>1/3</SUB>PO<SUB>4</SUB> is orthorhombic with the space group of <I>P</I>nma, which is same as Fe<SUB>1/3</SUB>Co<SUB>1/3</SUB>Ni<SUB>1/3</SUB>PO<SUB>4</SUB> during deintercalation. Temperature-dependent magnetization curves of Li<SUB>x</SUB>Fe<SUB>1/3</SUB>Co<SUB>1/3</SUB>Ni<SUB>1/3</SUB>PO<SUB>4</SUB> exhibit the enhancement of antiferromagnetic ordering due to the valence transition of transition metal ions with the increase in the Néel temperature from 35K for x=0 to 51K for x=1. The room-temperature Mössbauer spectra shows the valence transition with the LiFe<SUB>1/3</SUB>Co<SUB>1/3</SUB>Ni<SUB>1/3</SUB>PO<SUB>4</SUB> exhibiting Fe<SUP>2+</SUP> doublet whereas fully deintercalated Fe<SUB>1/3</SUB>Co<SUB>1/3</SUB>Ni<SUB>1/3</SUB>PO<SUB>4</SUB> showing one Fe<SUP>3+</SUP> doublet induced by the lithium ion diffusion. Experimental determined effective moment of Li<SUB>x</SUB>Fe<SUB>1/3</SUB>Co<SUB>1/3</SUB>Ni<SUB>1/3</SUB>PO<SUB>4</SUB> was found to be 5.63 <I>μ</I> <SUB>B</SUB> for x=0 and 6.95 <I>μ</I> <SUB>B</SUB> for x=1, which can be interpreted as incomplete absence of orbital contribution by crystal field around distorted MO<SUB>6</SUB> octahedron.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Li<SUB>x</SUB>Fe<SUB>1/3</SUB>Co<SUB>1/3</SUB>Ni<SUB>1/3</SUB>PO<SUB>4</SUB> (x=0, 1) material were synthesized via a solid state reaction method. </LI> <LI> Chemical delithiaition was performed by using NO<SUB>2</SUB>BF<SUB>4</SUB> oxidizing agent. </LI> <LI> The magnetic Néel temperatures of Li<SUB>x</SUB>Fe<SUB>1/3</SUB>Co<SUB>1/3</SUB>Ni<SUB>1/3</SUB>PO<SUB>4</SUB> were determined to be 51 for x=0 and 35K for x=1. </LI> <LI> The valence state of Fe ion can be provided the understanding of the charge/discharge mechanism for lithium-ion battery. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Choi, Hee June;Lee, Ji Min;Kim, Hyunkyung;Nam, Hye Jin;Shin, Hi-Jai R.;Kim, Dongha;Ko, Enyoung;Noh, Dong-Young;Kim, Keun II;Kim, Jung Hwa;Baek, Sung Hee Sookmyung Women's University Research Institute of 2011 여성과 건강 Vol.6 No.2
B-cell lymphoma 3 (Bc13) is a proto-oncogene upregulated in a wide range of cancers, including breast cancer. Although Bc13 is known to promote cell proliferation and inhibit apoptosis, the molecular mech¬anisms underlying the proto-oncogenic function of Bc13 have not been completely elucidated. To gain insight into the oncogenic role of Bc13, we applied a proteomic approach, which led to the identification of C-terminal binding protein 1 (CtBP1) as a binding partner of Bc13. A PXDLS/R motif embedded in Bc13 was found to mediate the interaction between Bc13 and CtBP1, which caused the stabilization of CtBP1 by blocking proteasome-dependent degradation. Apoptotic stimuli-induced degradation of CtBP1 was sig¬nificantly abolished by the upregulation of Bc13, leading to the sustained repression of pro-apoptotic gene expression and subsequent inhibition of apoptosis. Intriguingly, a strong positive correlation between the protein levels of Bc13 and CtBP1 was detected in breast cancer patient samples. Our study reveals a novel combinatorial role for Bc13 and CtBP1, providing an explanation for the acquisition of resistance to apop¬tosis in cancer cells, which is a major requirement for cancer development.
Characterization of Partially-inverted Zinc Ferrite with a Bio-Plasma Treatment
Hyunkyung Choi,Sam Jin Kim,Chul Sung Kim,최은하 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.69 No.5
ZnFe2O4 nanoparticles were prepared by using a high-temperature thermal-decomposition method and was investigated by using X-ray diffraction (XRD), high-resolution transmission electron spectroscopy (HR-TEM), MagneTherm, vibrating sample magnetometry (VSM) and M¨ossbauer spectroscopy. The XRD patterns revealed cubic spinel structures with space group Fd-3m. ZnFe2O4 nanoparticles were exposed to an argon plasma for 30 min. The self-heating temperature increased up to 37 C during plasma treatment for 30 min. Magnetic measurements showed that the blocking temperature increased from 72 to 78 K during the plasma treatment. A high saturation magnetization was obtained in the partially-inverted spinel. In order to confirm the cation distribution and the phase transition, we performed M¨ossbauer measurement. The M¨ossbauer spectra of ZnFe2O4 before and after plasma treatment showed Fe3+ valence states at room temperature. Also, the N´eel temperature of ZnFe2O4 was found to be larger after the plasma treatment.
Synthesis and Mössbauer studies of tavorite-structured LiFePO4F
Choi Hyunkyung,김철성,Lee Young Bae 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.80 No.12
A tavorite-structured LiFePO4F was synthesized using a two-step solid-state reaction as pure single phase without the impurity phase. Rietveld refnement using X-ray difraction showed that the crystal structure was triclinic with space group P 1. Temperature dependence magnetic susceptibility curve indicated an antiferromagnetic structure with a magnetic ordering, Néel temperature (TN), of 73 K. From inverse magnetic susceptibility curve, the Curie–Weiss temperature was ftted to−120 K. The spin reorientation temperature (TS) was determined to be 31 K by vibrating sample magnetometer and Mössbauer spectrometer. The Mössbauer spectra above TN was analyzed two doublets, indicating the Fe1(A) and Fe2(B) sites in FeF2O4 octahedra, while below TN, the spectra were ftted with sextet of two sets. The slope change of magnetic hyperfne feld and electric quadrupole splitting suggested contribution to the magnetic properties by spin–orbit coupling. The isomer shift for all temperatures indicates that the Fe charge state was Fe3+ ion state for both Fe1(A) and Fe2(B).
Mössbauer studies and inductive thermal properties of Mgx-doped maghemite nanoparticles
Choi Hyunkyung,김철성,Lee Young Bae 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.80 No.12
The Mgx-doped maghemite γ-Fe2O3 (x=0.05, 0.10, 0.15, and 0.20) were investigated, with the aim of enhancing the magnetic hyperthermia properties. We precisely tuned the magnetic and thermal properties of Mgx-doped γ-Fe2O3 prepared using a slightly modifed high-temperature thermal decomposition method. The analysis of X-ray difraction patterns confrmed the spinel phase, crystallite size, and lattice constant. Magnetization measurements performed on Mgx-doped γ-Fe2O3 revealed that the magnetization was maximum for the x=0.15 sample. Accordingly, this sample was exposed to plasma for 30 min. The thermal properties of Mgx-doped γ-Fe2O3 were studied with temperature rise dependent on magnetic hyperthermia measurements under an externally applied magnetic feld of 25 mT at 112 kHz. The change in magnetic properties before and after plasma treatment was investigated with Mössbauer spectroscopy and further analyzed with one sextet each for the tetrahedral A-site and octahedral B-site. The Fe ion state for each site was determined to be Fe3+ at all temperatures. It was confrmed that the hyperfne magnetic feld of the sample increased after plasma treatment.