• Korean Journal of Crystallography
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• v.13 no.3_4
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• pp.165-171
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• 2002

Single phase $Pb(Fe_{1/2}Ta_{1/2})O_3$, ceramics were successfully synthesized from the powders prepared by solid state reaction (sintering temperature: $1100^{\circ}C$, density: $9.3g/cm^3$, average grain size: $5.1{\pm}1.2mm$, space group: Pm3m). Their dielectric properties measured at $-150{\sim}50^{\circ}C$ showed the maximum relative dielectric constant of 31000 at $-41^{\circ}C$. 1 kHz, and typical relaxor ferroelectrics characteristics such as diffuse phase transition and dielectric relaxation phenomena. However, the diffuseness of phase transition decreased and the dielectric properties became more normal ferroelectrics as the time of annealing at $1000^{\circ}C$ increased. By using Raman spectroscopy, it was revealed that the $Fe^{3+}$ and $Ta^{5+}$ ions in the as-sintered $Pb(Fe_{1/2}Ta_{1/2})O_3$, are stoichiometrically 1 : 1 ordered within the short-range that can not be probed even by transmission electron microscopy, and this stoichiometric 1 : 1 ordering is enhanced by the annealing. The relaxor ferroelectric characteristics in the as-sintered $Pb(Fe_{1/2}Ta_{1/2})O_3$, could be correlated with the stoichiometric 1 : 1 short-range ordering of B-site cations, and the decrease of relaxor ferroelectric characteristics in the annealed $Pb(Fe_{1/2}Ta_{1/2})O_3$ could be correlated with the enhanced stoichiometric 1 : 1 short-range ordering of B-site cations.

• Bulletin of the Korean Chemical Society
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• v.30 no.6
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• pp.1274-1284
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• 2009

Single crystals of fully dehydrated and fully $Ca^{2+}$-exchanged zeolites A (|$Ca_6$|[$Si_{12}Al_{12}O_{48}$]-LTA) and X (|$Ca_{46}$| [$Si_{100}Al_{92}O_{384}$]-FAU) were brought into contact with Te in fine pyrex capillaries at 623 K and 673 K, respectively, for 5 days. Crystal structures of Te-sorbed $Ca^{2+}$-exchanged zeolites A and X have been determined by single-crystal X-ray diffraction techniques at 294 K in the cubic space group Pm$\overline{3}$ m (a = 12.288(2) $\AA$) and Fd $\overline{3}$ (a = 25.012(1) $\AA$), respectively. The crystal structures of pale red-brown |$Ca_6Te_3$|[$Si_{12}Al_{12}O_{48}$]-LTA and black coloured |$Ca_{46}Te_8$| [$Si_{100}Al_{92}O_{384}$]-FAU have been refined to the final error indices of $R_1/wR_2\;=\;0.1096/0.2768\;and\;R_1/wR_2$ = 0.1054/ 0.2979 with 204 and 282 reflections for which $F_o\;>\;4{\sigma}(F_o)$, respectively. In the structure of |Ca6Te3|[$Si_{12}Al_{12}O_{48}$]- LTA, 6 $Ca^{2+}$ ions per unit cell were found at one crystallographic positions, on 3-fold axes equipoints of opposite 6-rings. In |$Ca_{46}Te_8$|[$Si_{100}Al_{92}O_{384}$]-FAU, 46 $Ca^{2+}$ ions per unit cell were found at four crystallographically distinct positions: 3 $Ca^{2+}$ ions at Ca(1) fill the 16 equivalent positions of site I, 21 $Ca^{2+}$ ions at Ca(2) fill the 32 equivalent positions of site I’, 10 and 12 $Ca^{2+}$ ions at Ca(3) and Ca(4), respectively, fill the 32 equivalent positions of site II. The Te clusters are stabilized by interaction with cations and framework oxygen. In sodalite units, Te-Te distances of 2.86(10) and 2.69(4) $\AA$ in zeolites A and X, respectively exhibited strong covalent properties due to their interaction with $Ca^{2+}$ ions. On the other hand, in large cavity and supercage, those of 2.99(3) and 2.76(11) $\AA$ in zeolites A and X, respectively, showed ionic properties because alternative ionic interaction was formed through framework oxygen at one end and $Ca^{2+}$ cations at the other end.

• Korean Journal of Crystallography
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• v.8 no.2
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• pp.127-131
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• 1997

The crystal structure of a bromine sorption complex of vacuum-dehydrated Ag+ and Ca2+ exchanged zeolite A(a=12,234(1) Å) has been determined by single-crystal X-ray diffraction methods in the cubic space group Pm3m. The crystal was prepared by flow method using exchange solution in which mole ratio of AgNo3 and Ca(NO3)2 was 1:150 with a total concentration of 0.05M. The crystal was dehydrated at 360℃ and 2 ×10-6 Torr for 2days, followed by exposure to 180 Torr of Br2 vapor for 20min. full-matrix least-squares refinements converged to the final error indices of R1=0.111 and R2=0.101 using 90 reflections for which I>3o(I). About 3.1 Ag+ ions and 4.45 Ca2+ ions lie on the two crystallographically nonequivalent three-fold axes associated with 6-ring oxygens. A total of six bromine molecules are sorbed per unit cell. Each bromine molecule approaches a framework oxide ions axially (Br-Br-O=171(2)', O-Br=3.25(6) Å; and Br-Br=2,61(8) Å by a charge-transfer interaction.

• Journal of the Korean Magnetics Society
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• v.18 no.1
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• pp.24-27
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• 2008

We have prepared $MnFe_2O_4$ nanoparticles with polyol method. The crystallographic and magnetic properties were measured by using X-ray diffraction(XRD), vibrating sample magnetometer(VSM) and $M\"{o}ssbauer$ spectroscopy. The high resolution transmission electron microscope(HRTEM) shows uniform nanoparticle-sizes with $6{\sim}8$ nm. The crystal structure is found to be single-phase cubic spinel with space group of Fd3m. The lattice constant of $MnFe_2O_4$ nanparticles is determined to be $8.418{\pm}0.001{\AA}$. $M\"{o}ssbauer$ spectrum of $MnFe_2O_4$ nanparticles at room temperature(RT) shows a superparamagnetic behavior. In VSM analysis, the diagnosis of the superparamagnetic behavior is also shown in hysteresis loop at RT. $M\"{o}ssbauer$ spectrum at 4.2K shows that the well developed two sextets are with different hyperfine field $H_{hfA}=498$(A-site) and $H_{hfB}=521$(B-site) kOe.

• Bulletin of the Korean Chemical Society
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• v.30 no.3
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• pp.543-550
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• 2009

The single-crystal structure of largely ammonium-exchanged zeolite Y dehydrated at room temperature (293 K) and 1 ${\times}\;10^{-6}$ Torr. has been determined using synchrotron X-radiation in the cubic space group $Fd\overline{3}m\;(a=24.9639(2)\AA)$ at 294 K. The structure was refined to the final error index $R_1$ = 0.0429 with 926 reflections where $F_o>4\sigma(F_o)$; the composition (best integers) was identified as |$(NH_4)_{60}Na_{11}$|[$Si_{121}Al_{71}O_{384}$]-FAU. The 11 $Na^{+}$ ions per unit cell were found at three different crystallographic sites and 60 ${NH_4}^{+}$ ions were distributed over three sites. The 3 $Na^{+}$ ions were located at site I, the center of the hexagonal prism ($Na-O\;=\;2.842(5)\;\AA\;and\;O-Na-O\;=\;85.98(12)^{\circ}$). The 4 $Na^{+}$ and 22 ${NH_4}^{+}$ ions were found at site I' in the sodalite cavity opposite the double 6-rings, respectively ($Na-O\;=\;2.53(13)\;\AA,\;O-Na-O\;=\;99.9(7)^{\circ},\;N-O\;=\;2.762(11)\;\AA,\;and\;O-N-O =\;89.1(5)^{\circ}$). About 4 $Na^{+}$ ions occupied site II ($(Na-O\;=\;2.40(4)\;\AA\;and\;O-Na-O\;=\;108.9(3)^{\circ}$) and 29 ${NH_4}^{+}$ ions occupy site II ($N-O\;=\;2.824(9)\;\AA\;and\;O-N-O\;=\;87.3(3)^{\circ}$) opposite to the single 6-rings in the supercage. The remaining 9 ${NH_4}^{+}$ ions were distributed over site III' ($N-O\;=\;2.55(3),\;2.725(13)\;\AA\;and\;O-N-O\;=\;94.1(13),\;62.16(15),\;155.7(14)^{\circ}$).

• Korean Journal of Crystallography
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• v.6 no.2
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• pp.118-124
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• 1995

The crystal structure of an iodine sorption complex of vacumm-dehydrated Ag+ and Ca2+ exchanged zeolite A(a=12.174(3)Å) has been determined at 21℃ by single-crystal X-ray diffraction techniques in the cubic space group Pm3m. The crystal was prepared by flow method for three days using exchange solution in solution in which mole ratio of AgNO3 and Ca(NO3)2 was 1:150 with total concentration of 0.05 M. The complex was prepared by dehydration at 360℃ and 2×10-6 Torr for 2 days, followed by exposure to about 14.3 Torr of iodine vaporat 80℃ for 24 hours. Full-matrix least-squares refinement converged to the final error indices of R1=0.082, R2=0.068 using 122 reflections for which I > 3σ(I). Two Ag+ ions, 1.1 Ag+ ions, and 4.45 Ca2+ ions per unit cell are located on three different three-fold axes associated with 6-ring oxygens. Two Ag+ ions per unit cell are in the large cavity, 1.399(4)Å from the (111) plane of three oxygens. Another 1.1 Ag+ ions are found at opposite sites. Six iodine molecules are sorbed per unit cell. Each I2 molecule approaches a framework oxide ion axially (O-I=3.43(2)Å, I-I=2.92Å, I-I-O;166.1(3)°), by a charge transfer complex interaction. Two Ag+ ions make a close approach to the iodine molecules (Ag-I ; 2.73(2)Å).

• Korean Journal of Crystallography
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• v.7 no.1
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• pp.36-43
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• 1996

The crystal structure Tris(ethylenediamine)nickel(II)Dichromate has been determined by X-ray crystallography. Crystal data: a=8.268(2), b=13.865(2), c=14.921(2)Å, γ=102.04(2)°, V=1672.9(5)Å3, Z=4, Monocline, P21/b (space group No.=14), Dcalc=1.806 gcm-3, μ=24.05 cm-0.1. The intensity data were collected with Mo-Kα radiation(λ=0.7107Å) on an automatic four-circle diffractometer with a graphite monochromator. The structure was solved by Patterson method and refined by full matrix least-square methods using unit weights. The final R and S values were R=0.045, Rw=0.051, Rall=0.059 and S=2.171for 2248 observed reflections. The two carbon atoms of a ring of Ni(en)-ion were split into crossed four atoms. In consideration of α- and β-angles of two rings of a disordered ethylenediamine of Nien3-ion and the hydrogen bonds between Ni(en)3-cation and Cr2O7-anion, the configuration of Ni(en)3-ion is assumed to be disordered with Λδδδ and Λδδλ.

• Journal of the Korean Chemical Society
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• v.38 no.9
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• pp.621-627
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• 1994

Two crystal structures of dehydrated, $Ag^{+}$ and $Ca^{2+}$-exchanged zeolite A treated at $250^{\circ}C$ with 0.15 torr of Cs vapor have been determined by single-crystal X-ray diffraction technique in the cubic space group $Pm{\bar\3m$ at $21(1)^{\circ}C$ (a = 12.344(2) $\AA$ and 12.304(2) $\AA$). Their structures were refined to the final error indices, R (weighted), of 0.091 with 180 reflections, and 0.093 with 179 reflections, respectively, for which I > $3\sigma(I).$ In each structure, Cs species are found at four different crystallographic sites: 3 $Cs^{+}$ ions per unit cell are located at 8-ring centers, ca. 6.81∼7.14 $Cs^{+}$ ions are found on opposite 6-rings on threefold axes in the large cavity, ca. 1.93∼2.03 $Cs^{+}$ ions are found on threefold axes in the sodalite unit, and 0.53∼0.66 $Cs^{+}$ ions lie on opposite 4-rings. Also, ca. 4.12∼4.27 Ag atoms are located near the center of the large cavity. In these structures, excess cesium atoms in a unit cell are associated with other $Cs^{+}$ ions on a single threefold axis to form the linear cationic cluster $(Cs_4)^{3+}$. By blocking 8-rings, the $Cs^{+}$ ions may have prevented silver atoms from migrating out of the structure. The Ag atoms are likely to have formed hexasilver clusters at the centers of the large cavities. Each hexasilver cluster is stabilized by coordination to 14 $Cs^{+}$ ions.

• Bulletin of the Korean Chemical Society
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• v.17 no.7
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• pp.631-637
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• 1996

The structures of fully dehydrated Ca2+- and Rb+-exchanged zeolite X, Ca31Rb30Si100Al92O384(Ca31Rb30-X; a=25.009(1) Å) and Ca28Rb36Si100Al92O384(Ca28Rb36-X; a=24.977(1) Å), have been determined by single-crystal X-ray diffraction methods in the cubic space group Fd&bar{3} at 21(1) ℃. Their structures were refined to the final error indices R1=0.048 and R2=0.041 with 236 reflections for Ca31Rb30-X, and R1=0.052 and R2=0.043 with 313 reflections for Ca28Rb36-X; I>3σ(I). In both structures, Ca2+ and Rb+ ions are located at six different crystallographic sites. In dehydrated Ca31Rb30-X, sixteen Ca2+ ions fill site I, at the centers of the double 6-rings (Ca-O=2.43(1) Å and O-Ca-O=93.3(3)°). Another fifteen Ca2+ ions occupy site II (Ca-O=2.29(1) Å, O-Ca-O=119.5(5)°) and fifteen Rb+ ions occupy site II opposite single six-rings in the supercage; each is 1.60 Å from the plane of three oxygens (Rb-O=2.77(1) Å and O-Rb-O=91.1(4)°). About two Rb+ ions are found at site II', 1.99 Å into sodalite cavity from their three-oxygen plane (Rb-O=2.99(1) Å and O-Rb-O=82.8(4)°). The remaining thirteen Rb+ ions are statistically distributed over site III, a 48-fold equipoint in the supercages on twofold axes (Rb-O=3.05(1) Å and Rb-O=3.38(1) Å). In dehydrated Ca28Rb36-X, sixteen Ca2+ ions fill site I (Ca-O=2.41(1) Å and O-Ca-O=93.6(3)°) and twelve Ca2+ ions occupy site II (Ca-O=2.31(1) Å, O-Ca-O=119.7(4)°). Sixteen Rb+ ions occupy site II; each is 1.60 Å from the plane of three oxygens (Rb-O=2.81(1) Å and O-Rb-O=90.6(3)°) and four Rb+ ions occupy site II'; each is 1.88 Å into sodalite cavity from their three-oxygen plane (Rb-O=2.99(1) Å and O-Rb-O=83.8(2)°). The remaining sixteen Rb+ ions are found at III site in the supercage (Rb-O=2.97(1) Å and Rb-O=3.39(1) Å). It appears that Ca2+ ions prefer sites I and II in that order, and that Rb+ ions occupy the remaining sites. Rb+ ions are too large to be stable at site I, when they are competing with other smaller cations like Ca2+ ions.

• Bulletin of the Korean Chemical Society
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• v.15 no.3
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• pp.236-241
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• 1994

The crystal structures of $Cd_6-A$ evacuated at $2{\times}10^{-6}$ Torr and 750$^{\circ}$C (a=12.216(l) ${\AA}$), and of the product of its reaction with Rb vapor (a= 12.187(l) ${\AA}$), have been determined by single-crystal x-ray diffraction techniques in the cubic space group Pm$\bar{3}$m at 21(l)$^{\circ}$C. Their structures were refined to the final error indices, $R_1$=0.055 and $R_2$=0.067 with 191 reflections, and $R_1$=0.066 and $R_2$=0.049 with 90 reflections, respectively, for which I>3${\sigma}$(I). In dehydrated $Cd_6-A$, six $Cd^{2+}$ ions are found at two different threefold-axis sites near six-oxygen ring centers. Four $Cd^{2+}$ ions are recessed 0.50 ${\AA}$ into the sodalite cavity from the (111) plane at O(3), and the other two extend 0.28 ${\AA}$ into the large cavity from this plane. Treatment at 250 $^{\circ}$C with 0.1 Torr of Rb vapor reduces all $Cd^{2+}$ ions to give $Rb_{13.5^-}$A. Rb species are found at three crystallographic sites: three $Rb^+$ ions lie at eight-oxygen-ring centers, filling that position, and ca. 10.5 $Rb^+$ ions lie on threefold axes, 8.0 in the large cavity and 2.5 in the sodalite cavity. In this structure, ca. 1.5 Rb species more than the 12 $Rb^+$ ions needed to balance the anionic charge of zeolite framework are found, indicating that sorption of $Rb^0$ has occurred. The occupancies observed can be most simply explained by two "unit cell" compositions, $Rb_{12^-}A{\cdot}Rb$ and $Rb_{12^-}A{\cdot}2Rb$, of approximately equal population. In sodalite cavities, $Rb_{12^-}A{\cdot}Rb$ would have a $(Rb_2)^+$ cluster and $Rb_{12^-}A{\cdot}2Rb$ would have a triangular $(Rb_3)^+$ cluster. Each of the atoms of these clusters must bind further through a six-oxygen ring to a large cavity $Rb^+$ to give $(Rb_4)^{3+}$ (linear) and $(Rb_6)^{4+}$ (trigonal). Other unit-cell compositions and other cationic cluster compositions such as $(Rb_8)^{n+}$ may exist.