• Journal of Magnetics
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• v.19 no.1
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• pp.59-63
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• 2014

Nano-sized nickel substituted cobalt ferrite powders, $Ni_xCo_{1-x}Fe_2O_4$ ($0.0{\leq}x{\leq}1.0$), were fabricated by the sol-gel method, and their crystallographic and magnetic properties were studied. All the ferrite powders showed a single spinel structure, and behaved ferrimagnetically. When the nickel substitution was increased, the lattice constants and the sizes of particles of the ferrite powders decreased. The M$\ddot{o}$ssbauer absorption spectra of $Ni_xCo_{1-x}Fe_2O_4$ ferrite powders could be fitted with two six-line subspectra, which were assigned to a tetrahedral A-site and octahedral B-sites of a typical spinel crystal structure. The increase in values of the magnetic hyperfine fields indicated that the superexchange interaction was stronger, with the increased nickel concentration in $Ni_xCo_{1-x}Fe_2O_4$. This could be explained using the cation distribution, which can be written as, $(Co_{0.28-0.28x}Fe_{0.72+0.28x})[Ni_xCo_{0.72-0.72x}Fe_{1.28-0.28x}]O_4$. The two values of the saturation magnetization and the coercivity decreased, as the rate of nickel substitution was increased. These decreases could be explained using the cation distribution, the magnetic moment, and the magneto crystalline anisotropy constant of the substituted ions.

• Journal of the Mineralogical Society of Korea
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• v.26 no.1
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• pp.35-44
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• 2013

Synthetic carbon-coated olivine-like structured lithium iron phosphate ($Li^+Fe^{2+}(PO_4)^{3-}/C$) powder composites were compressed up to 35.0 GPa in the symmetrical diamond anvil cell at room temperature. Bulk modulus of $LiFePO_4/C$ was determined to be $130.1{\pm}10.3$ GPa. New peak appears at the d-spacing of 3.386 ${\AA}$ above 18 GPa, and another new one at 2.854 ${\AA}$ around 35 GPa. The crystallographic symmetry of the sample (i.e. orthorhombic) is apparently retained up to 35 GPa as no clear evidence for the phase transition into spinel structure has been observed. The pressure-induced volume change in the M1 site ($Li^+O_6$) is more significant than those in M2($Fe^{2+}O_6$) and $PO_4$ tetrahedral sites.

• Journal of the Mineralogical Society of Korea
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• v.12 no.2
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• pp.55-65
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• 1999

Spotted cordierite occurs as the result of intrusion of Wolaksan Granite of Cretaceous age in the northern part of the Ogcheon Metamorphic Belt, forming a contact metamorphic zoning in accordance with the distance from the granite body: a cordierite-muscovite-biotite-quartz assemblage and the higher-temperature cordierite-biotite-quartz-(cummingtonite). These quartz-ubiquitous mineral assemblages identified in the cordierite spot seem to reflect Al-deficient condition of the protolith. TEM observations of textural relations between the cordierite and mica within the cordierite spot clearly reflect that cordierite was formed at the expense of micaceous matrix. A structure refinement of the poikiloblastic cordierite was performed by the Rietveld refinement method. Unit cell of the cordierite was determined to be as follows : lower-temperature type: a=17.1480(9)${\AA}$, b=9.7743(6)${\AA}$, c=9.3184(5)${\AA}$, V=1561.9(4)${\AA}$3, higher-temperature type: a=17.136(2)${\AA}$, b=9.751(1)${\AA}$, c=9.322(1)${\AA}$, V=1557.7(4)${\AA}$3. They show a remarkable difference in the unit cell dimension. The refinement results indicate that structural sites of lower-temperature cordierite are wholly occupied by appropriating ions. Compared to this, tetrahedral sites of the higher-temperature type exhibit an order/disorder ranging about 5-8% as the result of substitution between Si4+ and Al3+, except for T26 site occupied wholly by Al3+. These structural differences seem to be related to the formation temperatures of both cordierite types.

• Journal of the Korean Ceramic Society
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• v.38 no.9
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• pp.817-821
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• 2001

A new $Mg_{2-x}MN_xSnO_4$ phosphor with an inverse spinel structure was synthesized by the solid-state reaction technique. The photoluminescence properties of the $Mg_2SnO_4$:Mn phosphors were investigated under 147nm -vacuum ultraviolet ray excitation. The Mn-doped $Mg_2SnO_4$ phosphor exhibited high emission intensity with the spectrum centered at 500nm wavelength. It was explained that the green emission in $Mg_2SnO_4$:Mn phosphor has originated from energy transfer from $^4T_1$ to $^6A_1$ of $Mn^{2+}$ ion at tetrahedral site of the spinel structure. The $Mn^{2+}$ ion concentration exhibiting the maximum emission intensity under the excitation of 147nm-vacuum ultraviolet ray was 0.25mol%. And the decay time of the phosphor was shorter than 10ms.

• Korean Journal of Materials Research
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• v.28 no.7
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• pp.371-375
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• 2018

The manganese-, nickel-, and aluminum-doped cobalt ferrite powders, $Mn_{0.2}Co_{0.8}Fe_2O_4$, $Ni_{0.2}Co_{0.8}Fe_2O_4$, and $Al_{0.2}CoFe_{1.8}O_4$, are fabricated by the sol-gel method, and the crystallographic and magnetic properties of the powders are studied in comparison with those of $CoFe_2O_4$. All the ferrite powders are nano-sized and have a single spinel structure with the lattice constant increasing in $Mn_{0.2}Co_{0.8}Fe_2O_4$ but decreasing in $Ni_{0.2}Co_{0.8}Fe_2O_4$ and $Al_{0.2}CoFe_{1.8}O_4$. All the $M{\ddot{o}}ssbauer$ spectra are fitted as a superposition of two Zeeman sextets due to the tetrahedral and octahedral sites of the $Fe^{3+}$ ions. The values of the magnetic hyperfine fields of $Ni_{0.2}Co_{0.8}Fe_2O_4$ are somewhat increased in the A and B sites, while those of $Mn_{0.2}Co_{0.8}Fe_2O_4$ and $Al_{0.2}CoFe_{1.8}O_4$ are decreased. The variation of $M{\ddot{o}}ssbauer$ parameters is explained using the cation distribution equation, superexchange interaction and particle size. The hysteresis curves of the ferrite powders reveal a typical soft ferrite pattern. The variation in the values of saturation magnetization and coercivity are explained in terms of the site distributions, particle sizes and the spin magnetic moments of the doped ions.

• Journal of the Korean Magnetics Society
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• v.7 no.5
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• pp.225-231
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• 1997

Sulphur Spinel $Co_{0.95}Fe_{0.05}Cr_2S_4$ has been studied with Mossbauer Spectroscopy between 4.2 K and room temperature. The $Fe^{2+}$ ion in a tetrahedral site is the Jahn-Teller active and the dynamic Jahn-Teller distortion starts below the magnetic ordering temperature. The distortion cause a quadrupole shift to appear which increases with decreasing temperature. The magnetic hyperfine field has a maximum at 100 k and then decreases with decreasing temperature. The magnitude of the interaction ratio R between the electric quadrupole and magnetic dipole interaction increases from 0 near the magnetic ordering temperature to 5.4 at 4.2 K. The optimum values of 0, the polar angle of the magnetic hyperfine field with respect to the principle axis of the electric field gradient (EFG) remains zero and the asymmetry of the EFG n is about 0.25. The simulations of Mossbauer spectra coincidence with the experimental results.

• Economic and Environmental Geology
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• v.21 no.3
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• pp.235-255
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• 1988

Talc deposit of pipe-like form occurrs in the lower part of the Hyangsanri Dolomite with a strike of N40 -50 E and a dip of 40 -50 NW which is one formation of the Ogcheon Super Croup. The pipi-like ore body plunge at about $40^{\circ}$ to the west and are parallel to the lineation developed in the area. Structural formulae of tales occurred in this deposit are close to the ieal composition $Mg_6Si_8O_{20}(OH)_4$ showing limited deviation from ideal one. Substitution of Al for Si in tetrahedral site is of little or nothing ranging 0-0.04 and octahedral occupancy is close to six ranging 5.88-5.98 atoms per unit cell. Predominant octahedaral cation is Mg and proportion of divalent cations is generally over 97percent. Calcite -dolomite thermometry is obtained by determining the mol % $MgCO_3$using of EPMA and XRD methods. The peak metamorphic temperature can be estimated at $470{\pm}30^{\circ}C$ in the area whereas carbonates occurred at near talc ore show lower temperature than $400^{\circ}C$ that the calcite solvus limit is not well established. It indicates that the talc deposit was formed at the lower temperature that the metamorphic temperature. Cosequently, the formation of talc by metamorphism is questionable and the alteratin zone developed around the talc ore is very limited. The occurrence of talc ore in the dolomite as well as mineralogy, calcite-dolomite geothermometry, chlorite geothermometry, field and microscopic evidence suggest that siliceous ascending hydrothermal solution along the fracture is responsible for the formation of talc. It was considered that the slight fracturing of dolomite was formed by deformation prior to the mineralization.

• Journal of the Korean Magnetics Society
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• v.6 no.6
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• pp.397-404
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• 1996

The magnetic properties of $Ni_{1-x}Zn_{x}Fe_{2}O_{4}$ have been studied by X-ray diffractometry and $M\"{o}ssbauer$ Spectroscopy at room temperature. The X-ray diffraction study show that spinel structure is formed in all x, lattice constants linearly increased from $8.3111{$\AA$}~8.4184{$\AA$}({\pm}0.0003)$ with increasing x from 0 to 1, and oxygen parameter increase with increasing x. $M\"{o}ssbauer$ spectrum shows that $Ni_{1-x}Zn_{x}Fe_{2}O_{4}(x=0)$ has two antiparallel magnetic structure due to $Fe^{3+}$ octahedral site and $Fe^{3+}$ tetrahedral site. $Ni_{1-x}Zn_{x}Fe_{2}O_{4}$ with $0.2{\leq}x{\leq}0.6$ has magnetic structure of Yafet and Kittel, in particularly, specimen with x=0.6 shows relaxation effect. Specimen with $x{\geq}0.8$ show paramagnetic quadrupole splitting. The isomer shift is independent of x, but quadrupole splittings decrease with increasing x in the range of $0.8{\leq}x{\leq}1$, and nuclear magnetic fields decrease with in¬creasing x in the range of $0{\leq}x{\leq}0.6$. The magnetic properties of $Ni_{1-x}Zn_{x}Fe_{2}O_{4}$ change from ferrimagnetics to pararnagnetics with increasing x.

• Journal of the Mineralogical Society of Korea
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• v.6 no.1
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• pp.17-26
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• 1993

Mineralogical characteristics of tosudite from the Sungsan and Bubson mines were studied and correlated using X-ray diffraction analysis, chemical analysis and electron microscopy. Tosudite occurs as an alteration product of Cretaceous volcanoclastic rocks in both mines. It is associated with microcrystalline quartz, dickite, illite/smectite or mica/smectite mixed-layer mineral. It forms cryptocrystalline aggregates with flaky habit. XRD analysis suggests that tosudite is an 1:1regularly interstratified dioctahedral smetite/dioctahedral chlorite. Bubsoo tosudite has more(00ℓ ) reflections and more periodice stacking sequence than Syngsan tosudite. Chemical analysis shows that tosudite is a Li-bearing aluminous 1:1 regularly interstrattified mineral composed of K-bedellite and donbassite. Cookeite component may be present in the chlorite layer. Bubsoo tosudite is more Al in tetrahedral site and Ca in interlayer, but less Al in octahedral site than Sugsan tosudite. Tosudite may be formed as the intermediate alteration products, forming after muscovite and before illite/smectite or mica/s$^{\circ}C$mectite, with the range from 100 $^{\circ}C$ to 360 ~ 480 $^{\circ}C$. The hydrothermal solution forming tosudite may be acidic solution with high activities of Si and Al.

• Journal of the Mineralogical Society of Korea
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• v.20 no.4
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• pp.313-325
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• 2007

In order to have better insights into adsorption of organic molecules on kaolinite surfaces, we performed quantum chemical calculations of interaction between three different model clusters of kaolinite siloxane surfaces and benzyl alcohol, with emphasis on the effect of size and lattice topology of the cluster on the variation of electron density and magnetic shielding tensor. Model cluster 1 is an ideal silicate tetrahedral surface that consists of 7 hexagonal rings, and model cluster 2 is composed of 7 ditrigonal siloxane rings with crystallographically distinct basal oxygen atoms in the cluster, and finally model cluster 3 has both tetrahedral and octahedral layers. The Mulliken charge analysis shows that siloxane surface of model cluster 3 undergoes the largest electron density transfer after the benzyl alcohol adsorption and that of model cluster 1 is apparently larger than that of model cluster 2. The difference of Mulliken charges of basal oxygen atoms before and after the adsorption is positively correlated with hydrogen bond strength. NMR chemical shielding tensor calculation of clusters without benryl alcohol shows that three different basal oxygen atoms (O3, O4, and O5) in model cluster 2 have the isotropic magnetic shielding tensor as $228.2{\pm}3.9,\;228.9{\pm}3.4,\;and\;222.3{\pm}3.0ppm$, respectively. After the adsorption, the difference of isotropic chemical shift varies from 1 to 5.5 ppm fer model cluster 1 and 2 while model cluster 2 apparently shows larger changes in isotropic chemical shift. The chemical shift of oxygen atoms is also positively correlated with electron density transfer. The current results show that the adsorption of benzyl alcohol on the kaolinite siloxane surfaces can largely be dominated by a weak hydrogen bonding and electrostatic force (charge-charge interaction) and demonstrate the importance of the cluster site and the lattice topology of surfaces on the adsorption behavior of the organic molecules on clay surfaces.