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갈륨 K 흡수단의 저온 EXAFS를 이용한 PbO-Ga$_2$O$_3$ 유리의 구조 해석
최용규,김경헌,허종,Choi, Yong-Gyu,Kim, Kyong-Hon,Chernov, Vladimir A,Heo, Jong 한국세라믹학회 1998 한국세라믹학회지 Vol.35 No.11
Ga K-edge EXAFS spectra of PbO-Ga2O3 glasses were recorded at liquid nitrogen temperature and analyz-ed in order to quantitatively understand the medium-range-order arrangement around gallium in the glasses. The second peak was generated from a backscattering of the neighbor balliums and the Ga-Ga distance is ~3.13 A with Ga coordination number of ~2.7 Therefore GaO4 tetrahedra are connected through the cor-ner~sharing mode and form their own clusters made of the tetrahedra sharing more than 3 corners while some chains or rings are also present. These connection schemes of the GaO4 tetrahedra are believed to form the substantial part of the network structure.
He, Maoshuai,Wang, Xiao,Zhang, Lili,Wu, Qianru,Song, Xiaojie,Chernov, Alexander I.,Fedotov, Pavel V.,Obraztsova, Elena D.,Sainio, Jani,Jiang, Hua,Cui, Hongzhi,Ding, Feng,Kauppinen, Esko Elsevier 2018 Carbon Vol.128 No.-
<P><B>Abstract</B></P> <P>The suitability of the NiMgO catalyst as a catalyst in chiral-selective growth of single-walled carbon nanotubes (SWNTs) by chemical vapor deposition has been assessed. It reveals that catalyst calcination temperature plays an important role in affecting the catalyst performances. Using CO as the carbon precursor and a chemical vapor deposition reaction temperature of 600 °C, NiMgO pre-calcined at 600 °C demonstrates the best performances in catalyzing the growth of SWNTs with predominant (6, 5) species. Systematic characterizations on catalysts calcinated at different temperatures indicate that Ni<SUP>2+</SUP> ions diffuse towards the interior of MgO matrix upon annealing. DFT-based calculations reveal that the binding energy between Ni<SUP>2+</SUP> and adjacent Ni(0) is larger than that between Mg<SUP>2+</SUP> and Ni (0), while Ni<SUP>2+</SUP> situated deep inside MgO has weak interactions with surface Ni atoms. This work highlights the importance of subsurface Ni<SUP>2+</SUP> in anchoring reduced surface Ni atom, which inhibits the aggregation of Ni particles and therefore, facilitates the growth of SWNTs with a narrow chirality distribution.</P> <P><B>Graphical abstract</B></P> <P>A Ni-incorporated MgO catalyst was developed for predominant synthesis of (6, 5) single walled carbon nanotubes. Density functional theory-based calculations revealed that the unreduced subsurface Ni stabilized reduced Ni atoms on the surface, facilitating the growth of carbon nanotubes with a narrow chirality distribution.</P> <P>[DISPLAY OMISSION]</P>
희토류 첨가 광소재의 나노구조 : Dy 첨가 Ge-As-S 유리의 X-선 흡수 스펙트럼 분석
최용규,송재혁,신용범,허종,Choi, Yong-Gyu,Song, Jay-Hyok,Shin, Yong-Beom,Chernov, Vladimir A.,Heo, Jong 한국세라믹학회 2006 한국세라믹학회지 Vol.43 No.3
Dy $L_3$-edge XANES and EXAFS spectra of chalcogenide Ge-As-S glass doped with ca. 0.2 wt% dysprosium have been investigated along with some reference Dy-containing crystals. Amplitude of the white-line peak in XANES spectrum of the glass sample turns out to be stronger than that of other reference crystals, i.e., $DY_2S_3,\;Dy_2O_3\;and\;DyBr_3$. It has been verified from the Dy $L_3$-edge EXAFS spectra that a central Dy atom is surrounded by $6.7{\pm}0.5$ sulfur atoms in its first coordination shell in the Ge-As-S glass, which is relatively smaller than 7.5 of the $Dy_2S_3$ crystal. Averaged Dy-S inter-atomic-distance of the glass ($2.78{\pm}0.01{\AA}$) also turns out to be somewhat shorter than that of the $Dy_2S_3$ crystal ($2.82{\pm}0.01{\AA}$). Such nanostructural changes occurring at Dy atoms imply there being stronger covalency of Dy-S chemical bonds in the Ge-As-S glass than in the crystal counterpart. The enhanced covalency in the nanostructural environment of $Dy^{3+}$ ions inside the glass would then be responsible for optical characteristics of the $4f{\leftrightarrow}4f$ transitions of the dopants, i.e., increase of oscillator strengths and spontaneous radiative transition probabilities.