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Mossbauer Studies of Olivine Fe1−yMnyPO4
권우준,심인보,김철성 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.12
The olivine-structured Fe1−yMnyPO4 (y = 0.0, 0.1, and 0.3), a possible cathode material forlithium-ion secondary battery, has been studied by using x-ray diffraction (XRD) and M¨ossbauerspectroscopy. These Fe1−yMnyPO4 samples were prepared by using the chemical lithium deintercalationprocess from LiFe1−yMnyPO4. The crystal structures of the Fe1−yMnyPO4 samples weredetermined to be orthorhombic (space group Pnma) at room temperature by using the Rietveldrefinement method. From the M¨ossbauer spectra at room temperature, the electric quadrupolesplitting (ΔEQ) and the isomer shift (δ) values of the Fe1−yMnyPO4 were determined to be ΔEQ= 1.512 mm/s, and δ = 0.31 mm/s for y = 0.0, ΔEQ = 1.502 mm/s, and δ = 0.31 mm/s for y =0.1, and ΔEQ = 1.382 mm/s, and δ = 0.31 mm/s for y = 0.3. The difference in the ΔEQ valuesfor Fe1−yMnyPO4 samples with varying Mn concentrations can be explained by the change in theexchange interaction due to the dependence of the asymmetry in the FeO6 octahedral sites on theMn concentration.
LiFe<SUB>0.9</SUB>Mn<SUB>0.1</SUB>PO<SUB>4</SUB> 물질의 결정구조 및 뫼스바우어 분광 연구
권우준(Woo Jun Kwon),이인규(In Kyu Lee),이찬혁(Chan Hyuk Rhee),김삼진(Sam Jin Kim),김철성(Chul Sung Kim) 한국자기학회 2012 韓國磁氣學會誌 Vol.22 No.1
The olivine structured LiFe<SUB>0.9</SUB>Mn<SUB>0.1</SUB>PO<SUB>4</SUB> material was prepared by solid state method, and was analyzed by x-ray diffractometer(XRD), superconducting quantum interference devices (SQUID) and Mossbauer spectroscopy. The crystal structure of LiFe<SUB>0.9</SUB>Mn<SUB>0.1</SUB>PO<SUB>4</SUB> was determined to be orthorhombic (space group: Pnma) by Rietveld refinement method. The value of Neel temperature (T<SUB>N</SUB>) for LiFe<SUB>0.9</SUB>Mn<SUB>0.1</SUB>PO<SUB>4</SUB> was determined 50 K. The temperature dependence of the magnetization curves showed magnetic phase transition from paramagnetic to antiferromagnetic at T<SUB>N</SUB> by SQUID measurement. Mossbauer spectra of LiFe<SUB>0.9</SUB>Mn<SUB>0.1</SUB>PO<SUB>4</SUB> showed 2 absorption lines at temperatures above T<SUB>N</SUB> and showed asymmetric 8 absorption lines at temperatures below T<SUB>N</SUB>. These spectra occurred due to the magnetic dipole and electric quardrupole interaction caused by strong crystalline field at asymmetric FeO<SUB>6</SUB> octahedral sites.
Thermal and Magnetic Properties of Melt-spun Co-Fe-B-Si-(Cr/Ta) Amorphous Alloys
조혜인,한보경,임혜인,권우준 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.3
The ferromagnetic amorphous alloys Co-Fe-B-Si-Cr and Co-Fe-B-Si-Ta were systemically investigated. [(Co<sub>1</sub>−<sub>x</sub>Fe<sub>x</sub>) <sub>0.75</sub>B<sub>0.2</sub>Si<sub>0.05</sub>]<sub>96</sub>Cr<sub>4</sub> (x = 0, 0.1, 0.4, 0.7, 1.0) and [(Co<sub>1−x</sub>Fe<sub>x</sub>)<sub>0.75</sub>B<sub>0.2</sub>Si<sub>0.05</sub>]<sub>96</sub>Ta<sub>4</sub> (x = 0, 0.1, 0.3, 0.5, 1.0) ribbons were prepared by using the melt-spinning technique. Amorphous structures were confirmed by the presence of a broad and halo peak in X-ray diffraction (XRD). The thermal characteristics, such as the glass transition temperature (<i>T<sub>g</sub></i>), the crystallization temperature (<i>T<sub>x</sub></i>) and the supercooled liquid region (Δ<i>T<sub>x</sub></i> = <i>T<sub>x</sub></i> − <i>T<sub>g</sub></i>), were measured by means of a differential scanning calorimeter (DSC). For the Co-Fe-B-Si-Cr alloys, the values of Δ<i>T<sub>x</sub></i> were in the range of 51.6 − 61.4 K, and for Co-Fe-B-Si-Ta alloys, they were in the range of 39.3 − 55.5 K. The magnetic properties were examined by means of a vibrating sample magnetometer (VSM) at a maximum field strength of 3000 Oe. These glassy ribbons exhibited soft magnetic properties. The saturation magnetization (<i>M<sub>s</sub></i>) and the coercive force (<i>H<sub>c</sub></i>) were in the ranges of 307.85 − 854.52 emu·cm<sup>3</sup> and 0.64 − 0.89 Oe, respectively.