• Bulletin of the Korean Chemical Society
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• v.18 no.6
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• pp.640-643
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• 1997

Pure titanium dioxide $(TiO_2)$ films were prepared by pulsed laser deposition on a single crystal Si(100) substrate. We have investigated the growth of crystalline titanium dioxide films with respect to substrate temperature and ambient oxygen pressure. The structural properties of the films were analyzed by X-ray diffraction. We found that the anatase as well as the rutile phases could be formed from the original rutile phase of the target $TiO_2$. At 0.75 torr of ambient oxygen pressure, the structure of $TiO_2$ film was amorphous at room temperature, anatase between 300 and 600 ℃, a mixture of anatase and rutile between 700 and 800 ℃, and only rutile at 900 ℃ and above. However, at a low ambient oxygen pressure, the rutile phase became dominant; the only rutile phase was obtained at the ambient oxygen pressure of 0.01 torr and the substrate temperature of 800 ℃. Therefore, the film structures were largely influenced by substrate temperature and ambient oxygen pressure.

• Journal of the Korean Magnetics Society
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• v.16 no.5
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• pp.261-263
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• 2006

In order to investigate the magnetic properties of Eu ions in the single crystal $MnF_2$, the temperature dependent magnetic susceptibilities of the antiferromagnetic $MnF_2$ and the single crystal $MnF_2$(1.5% $EuF_3$) with the rutile structures were measured in the temperature range from 4K to 300K. The detailed analysis of the measured susceptibilities showed that the magnetic susceptibility by the doping of the small amount $EuF_3$ in the antiferromagnetic single crystal $MnF_2$ follows the antiferromagnetic Curie-Weiss law with the negative paramagnetic Curie temperature similarly as in $MnF_2$. It was also found that Eu ion has +3 valence. This solves the long standing discrepancy on this problem.

• Journal of the Korean Magnetics Society
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• v.17 no.1
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• pp.1-5
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• 2007

The 1R(Infra-Red) spectrum and PL(Photoluminescence) of the antiferromagnetic pure $MnF_2$ and the single crystal $MnF_2(1.5%\;EuF_3)$ with the rutile structures were measured. The detailed analysis of the measured PL data showed the differences of the optical property between the single crystal $MnF_2(1.5%\;EuF_3)$ and the pure $MnF_2$. It was found that the additional PL peak by the doping of the $EuF_3$ in $MnF_2$ is originated from the f-d transition of $Eu^{3+}$ from the temperature dependent intensity measurement.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.15 no.5
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• pp.175-181
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• 2005

Ingots of rutile single crystals were grown by the skull melting method, and their characteristics were compared in terms of melt-dwelling time for each melt. The method is based on direct inductive heating of an electrically conducted melt by an alternating RF field, and the heating is performed by absorption of RF energy. $TiO_2$ is an insulator at room temperature but its electric conductivity increases elevated temperature. Therefore, titanium metal ring(outside diameter : 6cm, inside diameter : 4cm, thickness 0.2cm) was embedded into $TiO_2$, powder (anatase phase, CERAC, 3N) for initial RF induction heating. Important factors of the skull melting method are electric resistivity of materials at their melting point, working frequency of RF generator and cold crucible size. In this study, electric resitivity of $TiO_2$, $(10^{-2}\~10^{-1}\;{\Omega}{\cdot}m)$ at its melting point was estimated by compairing the electric resitivities of alumina and zirconia. Inner diameter and height of the cold crucible was 11 and 14cm, respectively, which were determined by considering of the Penetration depth $(0.36\~1.13cm)$ and the frequency of RF generator.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.17 no.3
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• pp.91-94
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• 2007

Single-crystalline $SnO_2$ nanowires were successfully grown on Si(001) substrates via vapor-liquid-solid mechanism in a thermal chemical vapor deposition. Large quantity of $SnO_2$ nanowires were synthesized at temperature ranges of $950{\sim}1000^{\circ}C$ in Ar atmosphere. It was found that the grown $SnO_2$ nanowires are of a tetragonal rutile structure and single crystalline by diffraction and transmission electron microscopy measurements. Broad emission located at about 600 m from the grown nanowires was clearly observed in room temperature photoluminescence measurements, indicating that the emission band originated from defect level transition into $SnO_2$ nanowires.

• Journal of the Korean Chemical Society
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• v.59 no.3
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• pp.238-245
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• 2015

The crystallization and morphology change of amorphous titanias by hydrothermal treatment have been investigated. The amorphous titanias were prepared by pure water hydrolysis of two different precursors, titanium tetraisopropoxide (TTIP) and TTIP modified with acetic acid (HOAc) and characterized prior to hydrothermal treatment. In order to avoid complicate situation, the hydrothermal treatment was performed in a single solvent water with and without strong acids at various temperatures. The effects of strong acid, temperature and time were systematically investigated on the transformation of amorphous titania to crystalline TiO₂ under simple hydrothermal condition. Without strong acid the titanias were transformed into only anatase phase nanoparticle regardless of precursor type, temperature and time herein used (up to 250 ℃ and 48 hours). The treatment temperature and time effected only on the crystalline size, not on the crystal phase et al. However, it was clearly revealed that the strong acids such as HNO₃ and HCl catalyzed the formation of rutile phase depending on temperature. HCl was slightly better than HNO₃ in this catalytic activity. The morphology of rutile TiO₂ formed was also a little affected by the type of acid. The precursor modifier, HOAc slightly reduced the catalytic activity of the strong acids in rutile phase formation.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.22 no.1
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• pp.25-28
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• 2012

Tin-oxide ($SnO_2$) nanowires have been synthesized on one-dimensional (1D) carbonization cotton fabric using chemical vapour deposition method. One-dimensional (1D) carbonization cotton fabric has been synthesized from cotton fabric using annealing process in nitrogen gas at $1000^{\circ}C$. The $SnO_2$ nanowires are single-crystalline rutile structures with 20 nm in diameter and 10 ${\mu}m$ in length. Scanning electron microscopy (SEM), x-ray photoelectron spectroscopy, Raman spectroscopy, transmission electron microscopy and photoluminescence (PL) spectroscopy were utilized to characterize the as-synthesized products.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.1
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• pp.35-42
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• 2010

In this paper, three types of CNT/$TiO_2$ composite electrodes were prepared with different methods. The changes in XRD patterns showed that the Electrode A contained a mixed phase of anatase and rutile while the Electrode B and Electrode C contained a typical single and clear anatase crystal structure. From SEM micrographs, $TiO_2$ particles were adhered on the surface of the CNT network in the forms of small clusters. The results of chemical elemental analysis indicated that the main elements such as C, O and Ti were existed. The results demonstrated that the efficiency of photoelectrocatalytic (PEC) oxidation for methylene blue (MB) was higher than that of photocatalytic (PC) oxidation. There was a clear enhancement trend of the MB degradation using the prepared CNT/$TiO_2$ composite electrodes with an increase of applied potential. Finally, the prominent PEC activities of the CNT/$TiO_2$ composites could be attributed to combination effects of photo-degradation of $TiO_2$, electron assistant of CNT and function of applied potential.

• Journal of the Korean Chemical Society
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• v.30 no.1
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• pp.19-26
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• 1986

A titanium oxide thin films were prepared by air oxidation and vapour oxidation and a $TiO_2$ single crystal was reduced by heating in an argon atmosphere. All the electrode characteristics of the Ti$O_{2-x}$, thin films are not different from those of slightly reduced single crystal rutile. In cyclic voltammogram of oxygen containing electrolyte solution at Ti$O_{2-x}$ electrodes, cathodic peaks were observed at between -0.8V and -1.0V vs. SCE. The cathodic current near 0V vs. SCE in saturated solution with nitrogen was observed to be greater than in saturated solution with air. The chronoamperogram was represented by the equation of i = $i_0e^{-kt}$, when the rate constant k was represented by the equation of k =$k_0{[H^+]}^nexp(A{\eta}+E_a/RT)$ The values of activation energy $E_a $were found to be 4.6~4.8kcal/mole in overpotential range of 0.035∼0.145 V and 1.6kcal/mole in overpotential range of 0.2∼0.5V. The values of n and A were found to be 0. 1 and 5.4~5.6/V in range of 0.035~0.145V, and in range of 0.2~0.5V, to be 0.04 and 1.3/V, respectively. This can be interpreted as an totally irreversible reduction of oxygen.