• Journal of the Korean Magnetics Society
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• v.8 no.2
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• pp.67-73
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• 1998

Crystallographic and magnetic properties of perovskite $Gd_{1-x}Sr_xFeO_{3-y}$ (x=0.0, 0.5) substituted $Sr^{2+}$ having larger inoic radius than $Gd^{3+}$ at GdFeO$_3$have been studied by x-ary diffraction, M$\ "{o}$ssbauer spectroscopy, and VSM. The cystal structures are found to be orthorhombic with the lattice parameters : $a_o=5.53\;{\AA},\;b_o=5.608\;{AA},\;C_o=7.724\;{\AA}$ for $Gd_{0.5}Sr_{0.5}FeO_{3-y}$ (x=0.0, 0.5) have been investigated over temperature range from 4.2 to 690 K using the M$\ "{o}$ssbauer technique. The Neel temperatuer of $Gd_{1-x}Sr_xFeO_{3-y}$ system is 690 K with x value of 0.0 and 515 K with x value of 0.5. Analysis of M$\ "{o}$ssbauer spectra Mohr's salt analysis for $Gd_{1-x}Sr_xFeO_{3-y}$ demonstrated the existence of the mixed valence states of iron and the coordination state of $Fe^{3+}$ and $Fe^{4+}$ ions. The Corresponding hyperfine parameters for GdFeO$_3$ are compatible with S=5/2 $Fe^{3+}$ in octahedral cooedination.l cooedination.

• Journal of the Korean Ceramic Society
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• v.18 no.3
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• pp.152-156
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• 1981

$Fe_2O_3$ was reduced over the temperature range of 600-100$0^{\circ}C$ in both the atmospheres for the Fe-stable and FeO-stable states. It was found that the reduction follows first order kinetics and the reduction of $Fe_3O_3$ to $Fe_3O_4$ is the rate-controlling step.

• Journal of the Korean Ceramic Society
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• v.26 no.5
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• pp.705-711
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• 1989

The glass-ceramics was prepared with the scoria(CaO-MgO-Al2O3-SiO2 system) of the locally occurring volcanic ejecta containing 10-13w/o of (FeO＋Fe2O3) by melting at 140$0^{\circ}C$ for 4 hours and thermally treated for nucleation and crystallization. The sucrose was added to the scoria to adjust the Fe2+/Fe3+ ratio during the melting process. The addition of 1-2w/o of sucrose showed the glass-ceramics body with the finest particle developed and dispersed over the entire range. It is concluded that the impurity content of iron oxide and titanium oxide play the most-influencial effect on the crystallization. When 1-2w/o of sucrose was added to the scoria, the value of Fe2+/Fe3+ ratio was 0.93-1.32 and showed the best result of crystallization. The nucleation temperature and time were calculated by the measurements of exothermic peak temperatures of DTA for quenched and thermally treated glasses. The nucleation temperature of scoria glass without the addition of sucrose was estimated as 75$0^{\circ}C$, but the addition of sucrose by 2w/o showed the nucleation temperature 6$25^{\circ}C$. The nucleation time was calculated with the same DTA curves. The nucleation times estimated were about 150min. for both of glasses without and with sucrose added. Finally, the activation energies for crystallization were calculated with the DTA data. The calculated activation energies were 143 Kcal/mole for the glass without addition of sucrose and 90Kcal/mole, 87Kcal/mole, 85Kcal/mole and 71Kcal/mole for the glasses of 1w/o, 2w/o, 3w/o and 4w/o addition respectively.

• Journal of the Korean Magnetics Society
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• v.9 no.1
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• pp.17-22
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• 1999

Hexagonal M-type barium ferrite $BaFe_{12}O_{19}$ was prepared by a direct solid state reaction between $BaCO_3$ and ${\Alpha}-Fe_2O_3$ powders at temperatures ranging from 800 to 1000 $^{\circ}C$ in a nitrogen or air environment. The effects of NaCl on phase transformation of mixture of $BaCO_3$ and ${\Alpha}-Fe_2O_3$ to $BaFe_{12}O_{19}$ were studied using X-ray diffraction and M$\"{o}$ssbauer spectroscopy. Regardless of the environment for heat treatment or the added NaCl, two phases, BaFe and ${\Alpha}-Fe_2O_3$, coexist for samples heat treated at 800 $^{\circ}C$, but a single phase was observed from samples heat treated at 100$0^{\circ}C$ in both air and nitrogen environments. It was found that the addition of NaCl reduced the amount of $a-Fe_2O_3$ phase.hase.

• Journal of the Korean Ceramic Society
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• v.39 no.9
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• pp.863-870
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• 2002

The Single phase $Pb(Fe_{1/2}Ta_{1/2})O_3$ (x=0.0∼1.0) solid solutions were successfully synthesized and their ordering structures as well as dielectric properties were investigated ${{r(Nb^{5+})=r(Ta^{5+})=0.78 {\AA},\;AW(Nb^{5+})=92.91,\;AW(Ta^{5+})=180.95}}$. While $Pb(Fe_{1/2}Ta_{1/2})O_3$ showed typical relaxor ferroelectric characteristics such as dielectric relaxation and diffuse phase transition, the sharpeness of the phase transition increased as $Ta^{5+}$ was replaced by $Nb^{5+}$ and finally $Pb(Fe_{1/2}Nb_{1/2})O_3$ showed normal ferroelectric characteristics with no dielectric relaxation. By using Raman spectroscopy, it was revealed that the $Fe^{3+}\;and\;Ta^{5+}\;of\;Pb(Fe_{1/2}Ta_{1/2})O_3$ were stoichiometrically 1:1 ordered within the short range which can be hardly probed even by TEM. Also, The degree of ordering in $Pb(Fe_{1/2}Ta_{1/2})O_3$ decreased as $Ta^{5+}$ was replaced by $Nb^{5+}$ and finally $Fe^{3+}\;and\;Nb^{5+}\;of\;Pb(Fe_{1/2}Nb_{1/2})O_3$ were completely disordered. The relaxor ferroelectric characteristics of $Pb(Fe_{1/2}Ta_{1/2})O_3$ could be correlated with the stoichiometric 1:1 ordering of B-site cations within the short range which can be hardly probed even by TEM. Also, the decrease of the relaxor ferroelectric characteristics with the replacement of $Ta^{5+}\;by\;Nb^{5+}$ could be correlated with the weakening of the ordering and the normal ferroelectric characteristics of $Pb(Fe_{1/2}Nb_{1/2})O_3$ could be correlated with the complete disordering of B-site cations.

• Journal of the Korean Magnetics Society
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• v.24 no.5
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• pp.135-139
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• 2014

Iron-oxide nanopowders were synthesized by a pulsed wire evaporation (PWE) in various ambient gas conditions. SEM measurement indicates that the spherical iron nanoparticles are about 50 nm in diameter. The phase analysis for the produced iron-oxide powders was systematically investigated by using $M\ddot{o}ssbauer$ spectra and the results show that classified phases of $Fe_2O_3$ and $Fe_3O_4$ can be controlled by regulating the oxygen concentration in the mixed gas during the PWE process. A quadrupole line on the center of $M\ddot{o}ssbauer$ spectrum represents the superparamagnetic phase of 12 % from ${\gamma}-Fe_2O_3$ phase.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.10
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• pp.935-941
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• 2006

In this paper, the dielectric and piezoelectric properties of $0.4Pb(Ni_{1/3}Nb_{2/3})O_3+0.6Pb(Zr_{405}Ti_{595})O_3+X\;wt%\;Fe_2O_3$ ceramics were investigated with the addition of $Fe_2O_3$ and sintering temperature. Dielectric constant and piezoelectric constant increased with amount of $Fe_2O_3$ to 0.25 wt% and then decreased the further addition of $Fe_2O_3$. It seems that $Fe_2O_3$ acts as a sintering aid at the sintering temperature of $1150^{\circ}C$. By the addition of $Fe_2O_3$., sintering temperature of the system was lowered from $1250^{\circ}C\;to\;1100^{\circ}C$. The piezoelectric properties showed the maximum value of ${\varepsilon}r=4669,\;d_{33}=810(10^{-12}m/V)$, kp = 77 %, Qm = 55, in $0.4Pb(Ni_{1/3}Nb_{2/3})O_3\;-0.6Pb(Zr_{0.405}Ti_{0.595})O_3+0.25wt%\;Fe_2O_3$ ceramics having composition near the morphotropic phase boundary. The composition may be appropriate for actuator materials because of high piezoelectric constant and electromechanical coupling factor.

• Journal of the Korean Ceramic Society
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• v.39 no.3
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• pp.226-232
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• 2002

We searched thermal stability of ${\alpha}-Fe_2O_3$ using red color filter for display. In the PDP(Plasma Display Panel), the color filter layer is lied normally between front glass and transparent dielectric materials, so it might be needed to study the reaction of ${\alpha}-Fe_2O_3$ and transparent dielectric materials. The transparent dielectric materials containing ZnO has good transparency. Red colorlayer of ${\alpha}-Fe_2O_3$ contacted with dielectric material layer containing ZnO is changed to colorlessness over 500$^{\circ}$C because ZnO defuse ${\alpha}-Fe_2O_3$, the dielectric materials without ZnO, however, maintain red color at the same condition. We suggest that a layer contacting with ${\alpha}-Fe_2O_3$ red color layer has to lie with transparent dielectric materials without ZnO, then the materials containing ZnO is coated over to get color of ${\alpha}-Fe_2O_3$ for red color filter

• Journal of the Korean Ceramic Society
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• v.35 no.12
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• pp.1301-1307
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• 1998

For dolomite clinkers used as stamp materials the corrosion behavior of those by molten steel was investigated in therange of temperatures between 1550$^{\circ}C$ and 1600$^{\circ}C$ IN hot face the dicalciumferrite of magnesioferrite and dicalciumferrite formed within dolomite clinkers was preferentially dissolved into molten steel and the protective layer of magnesioferrite was formed. For dolomite clinker without Fe2O3 magnesioferrite maintained the skeleton of MgO while the skeleton of CaO disappered bythe formation of dicalciumferrite and it existed as grain boundary phases of magnesioferrite. For dolomite clinker with Fe2O3 was diffused into hot face by the decomposition of dicalciumferrite. With increasing temperature of molten steel the formation depth of dicalciumferrite was increased and the magnesioferrite layer in hot face was decreased for dolomite clinker without Fe2O3 while the layer thickness and grain sizes of magnesioferrite in hot face was decreased for dolomite clinker without Fe2O3 while the layer thickness an grain sizes of magnesioferrite in hot face was increased due to the increment of the decomposition reaction of dicalciumferrite for dolomite clinker with Fe2O3.

• Journal of the Korean Magnetics Society
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• v.10 no.4
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• pp.165-170
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• 2000

The purpose of this study is to investigate the effect of annealing conditions on physical and magnetic properties of Fe-Hf-N thin films. When the thin films were annealed in $N_2$ gas, a surface oxide layer, comprised of Fe$_2$O$_3$ and Fe$_3$O$_4$, was formed at the surface of the thin films and a Fe-Hf-O-N layer was also formed under this surface oxide layer. It was found that the thicknesses of the surface oxide layer and the Fe-Hf-O-N layer increased, as the annealing temperature increased. It was also found that if the thickness of the surface oxide layer was excluded in the property calculation, the soft magnetic properties of the annealed thin films were not much different from those of the as-deposited thin films. Therefore, it was suggested that the Fe-Hf-O-N layer formed under the surface oxide layer did not lose significantly the soft magnetic properties of the Fe-Hf-N films and the Fe-Hf-N films annealed in $N_2$gas showed the soft magnetic properties of the Fe-Hf-N and Fe-Hf-O-N multi-layers.