• Journal of Magnetics
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• v.20 no.1
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• pp.26-30
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• 2015

The crystallographic and magnetic properties of gallium-substituted cobalt ferrite ($CoGa_xFe_{2-x}O_4$) were investigated. The new material was synthesized using conventional ceramic methods, with gallium substituted for ferrite in the range of x = 0.0 to 1.0, in steps of 0.2. X-ray diffraction and M$\ddot{o}$ssbauer spectroscopy were used to confirm the presence of crystallized particles in the $CoGa_xFe_{2-x}O_4$ ferrite powders. All of the samples exhibited a single phase with a spinel structure, and the lattice parameters decreased as the gallium content increased. The particle size of the samples also decreased as gallium increased. For $x{\leq}0.4$, the M$\ddot{o}$ssbauer spectra of $CoGa_xFe_{2-x}O_4$ could be fitted with two Zeeman sextets, which are the typical spinel ferrite spectra of $Fe^{3+}$ with A- and B-sites. However, for $x{\geq}0.6$, the M$\ddot{o}$ssbauer spectra could be fitted with two Zeeman sextets and one doublet. The variation in the M$\ddot{o}$ssbauer parameters and the absorption area ratio indicated a cation distribution of $(Co_{0.2-0.2x}Ga_xFe_{0.8-0.6x})[Co_{0.8+0.2x}Fe_{1.2-0.4x}]O_4$, and the magnetic behavior of the samples suggested that the increase in gallium content led to a decrease in the saturation magnetization and in the coercivity.

• Applied Chemistry for Engineering
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• v.9 no.2
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• pp.220-225
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• 1998

The spinel structured $LiMn_2O_4$ was prepared from $Li_2CO_3$ and $MnO_2$ by calcination at various temperatures in the range of $750{\sim}900^{\circ}C$. It was found that the most suitable cubic structure of $LiMn_2O_4$ was obtained by heating at $850^{\circ}C$ for 12 hrs. However, in the calcination at $900^{\circ}C$, $Mn^{4+}$ of 0.06M was changed to $Mn^{+3}$ by the oxygen loss, so that it has been shown that the formula has changed to $LiMn_2O_{3.97}$. This phenomena were in agreement with the Jahn-Teller distortion by the increment of $Mn^{+3}$ ion on the octahedral sites of the spinel structured $LiMn_2O_4$. The results showed that after 15 charge/discharge cycles in the voltage range from 3.5V to 4.3V versus Li/$Li^+$ with a current density of $0.25mA/cm^2$, the spinel structured $LiMn_2O_4$ that was prepared at $900^{\circ}C$ showed a lower discharge capacity, 82~50 mAh/g, while the $LiMn_2O_4$, prepared at $850^{\circ}C$, showed the discharge capacity of 102~64 mAh/g.

• Journal of the Korean Magnetics Society
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• v.14 no.1
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• pp.33-37
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• 2004

Cu$_{0.1}$Fe$_{0.9}$Cr$_2$S$_4$ has been studied with Mossbauer spectroscopy, x-ray diffraction, vibrating sample magnetometer (VSM), and magnetoresistance (MR) measurement. The crystal structure was determined to be a cubic spinel with lattice parameter a$_{0}$=9.9880 $\AA$. The MR measurements show a semiconductor behavior below 110 K and metal behaved above 100 K. The temperature dependence of magnetization of Cu$_{0.1}$Fe$_{0.9}$Cr$_2$S$_4$ was reported. In addition to a large irreversibility between the zero-field-cooling (ZFC) and the field-cooling (FC) magnetization at applied field H=100 Oe, a cusp-like anomaly was observed in both the FC and ZFC curves. It shifted toward the lower temperature region with increasing magnetic field, and then showed convex type maximum at 110 K, under the applied field of 5 kOe. The Mossbauer spectra were measured from 15 K to room temperature. The asymmetric line broadening was observed for the sample Cu$_{0.1}$Fe$_{0.9}$Cr$_2$S$_4$, and it was considered to be dynamic Jahn-Teller relaxation. The charge state of Fe ions was ferrous in character. The unusual reduction of magnetic hyperfine field below 110 K was interpreted in terms of cancellation effect between the mutually opposite orbital current field (H$_{L}$) and Fermi contact field (H$_{C}$).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.10
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• pp.4660-4665
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• 2011

New precursors as a Li adsorbent, $Li_{1.6}(MnM)_{1.6}O_4$ (M=Cu, Ni, Co, Fe), were synthesized by hydrothermal method and their physicochemical properties were discussed. XRD and HRTEM results revealed that the original spinel structure was stabilized by cobalt-doping while Cu-, Ni- and Fe-doping led to structural changes. Such a structural stabilization by Cobalt-doping was maintained after lithium leaching by acid treatment. Li absorption efficiency from seawater was significantly enhanced by using the Cobalt-doped spinel manganese oxide, $Li_{1.6}[MnCo]_{1.6}O_4$, compared to the commercially available $Li_{1.33}Mn_{1.67}O_4$; the adsorbed amount of Li from 1g-adsorbent was 35 and 16 mg by $Li_{1.6}[MnCo]_{1.6}O_4$, and $Li_{1.33}Mn_{1.67}O_4$, respectively.

• Journal of the Mineralogical Society of Korea
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• v.1 no.2
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• pp.94-103
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• 1988

Diamond anvil cell (DAC) interfaced with a YAG laser heating system has been used to study the phase transformations on perovskite structured titanates ($BaTiO_3$, and $PbTiO_3$) and to synthesize the silicate perovskite phase from the orthopyroxenes of $MgSiO_3$ and $(Mg_{0.87},\;Fe_{0.13})SiO_3$. $BaTiO_3$ and $PbTiO_3$ transform from tetragonal phase to cubic at the pressures of approximately 2.6 GPa and 4.0 GPa at room temperature, respectively. Cubic phases of the both show wide range of stability in the extended in-situ high pressures and high temperature regions. Starting orthoenstatite of $MgSiO_3$ has yielded the perovskite phase as the major structure with ilmenite, gamma-spinel, betta-spinel and stishovite phases at ~38 GPa and ${\sim}1,000^{\circ}C$. $(Mg_{0.87},\;Fe_{0.13})SiO_3$ has shown the perovskite as the major phase with betta-spinel, stishovite and enstatite phases at ~35 GPa and ${\sim}1,000^{\circ}C$. The ilmenite phase does not occur at this condition.

• Journal of the Korean Vacuum Society
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• v.20 no.3
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• pp.205-210
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• 2011

Structural and electrochemical properties of spinel oxide $LiMn_2O_4$ thin films prepared by using a sol-gel method on Pt/Ti/$SiO_2$/Si substrates were investigated. When Li/Mn molar ratio of the film was smaller than 0.5, $Mn_2O_3$hase was found to coexist with $LiMn_2O_4$. Half-cell batteries fabricated using the $LiMn_2O_4$ films as the cathode were put into chargedischarge (C-D) cycles and the change in structural properties of the cathode after the cycles was examined by X-ray diffraction and Raman spectroscopy. As the C-D cycle number increases, the discharge capacity of pure $LiMn_2O_4$ battery gradually decreases, being reduced to 72% of the initial capacity at 300 cycles. Such capacity fading is attributable to the decrease in the number of $Li^+$ ions that return to the tetrahedral sites of the spinel structure during the discharge step and the resultant increase in $Mn^{4+}$ density in the film. Also, $Mn_2O_3$ phase gradually appeared in the film as the cycle number increases.

• Korean Journal of Materials Research
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• v.5 no.2
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• pp.239-245
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• 1995

Mn-Zn ferrite thin films were deposited on $SiO_2(1000 \AA)/Si(100)$ by ion beam sputtering using a single ion source. A mosaic target consisting of a single crystal(ll0) Mn-Zn ferrite with a Fe metal strip on it was used. As-deposited films without oxygen gas flow have a wiistite structure due to oxygen deficiencies, which originated from the extra metal atoms sputtered from the metal strips during deposition. The as-deposited films with oxygen gas flow, however, have a spinel structure with (111) preferred orientation. The crystallization of thin films was maximized at the ion beam extraction voltage of 2.lkV, at which the deposited films are bombarded appropriately by the energetic secondary ions reflected from the target. As the extraction voltage increased or decreased from the optimum value, the crystallinity of thin films becomes poor owing to a weak and severe bombardment of the secondary ions, respectively. Crystallization due to the bombardment of the secondary ions was also maximized at the beam incidence angle of $55^{\circ}$. The as-deposited ferrite thin films with a spinel structure showed ferrimagnetism and had an in-plane magnetization easy axis.

• Journal of the Korean Ceramic Society
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• v.39 no.1
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• pp.12-15
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• 2002

Ultrafine cadmium ferrite particles have been investigated by X-ray diffractometry, transmission electron microscopy and SQUID magnetometry. All peaks of X-ray diffraction patterns are broad, but correspond to a cubic spinel structure with the lattice constant of 8.65 $\AA$. The average particle size determined by TEM is 9.7 nm and the size distribution of particles is not normal, but lognormal. The maximal magnetization measured at 5 K was 17.7 emu/g. The experimental data show a transi-tion from a disorder ferrimagnetic phase to a spin-glass phase (i.e. reentrant behavior) with a freezing temperature (T$\_$f/) of 30 K. Superparamagnetic behavior of the particles is confirmed by the coincidence of the plots of M vs. H/T for 100 and 300 K.

• Journal of the Korean Ceramic Society
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• v.29 no.12
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• pp.981-989
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• 1992

This is a study on the effects of cristobalite transition of quartz in semi-vitrious whiteware body, as addition of alkali and alkali earth oxides, prepared by pottery stone, feldspar, kaolin and clay minerals. The amounts of ${\alpha}$-quartz to ${\alpha}$-cristobalite transition, F.O.C. (fraction of cristobalite), were increased with firing temperature. In MgO added body, ${\alpha}$-quartz was decreased and the formation of cristobalite was increased. Effects of K2O addition was remarkably decreased the formation of cristobalite. Additive effects of MgO and K2O were confirmed that it was very different to variation of transition temperature of metakaolinite to Si-Al spinel structure in thermal reaction of kaolinite minerals. Result CaO addition was ineffective to transition temperature, and the transition temperature in Na2O added body was decreased, but relative intensity of quartz and cristobalite crystal in XRD results was decreased. This was characterized by the effects on the formation of liquid phase much more.

• The Korean Journal of Ceramics
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• v.5 no.3
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• pp.303-305
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• 1999

Ultrafine cobalt ferrite particles have been synthesized using a microemulsion method. All peaks of X-ray diffranction patterns are fairly broad but correspond to a cubic spinel structure with the lattice constant 8.39$\AA$. The coercivity measureed at 5K is 15.1 kOe. The maximal magnetization measured at 5 and 300 K are 13.2 and 10.7 emu/g, respectively. The particles behave ferrimagnetically at 5 K but superparamagnetically at 300K. Superparamagnetic behavior of the particles at room temperature was confirmed by the conincidence of the M vs. H/T at different temperatures and the Mossbauer spectrum.