• Journal of the Korean Ceramic Society
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• v.49 no.4
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• pp.380-384
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• 2012

This paper deals with the recent developments of high thermal conductivity silicon nitride ceramics. First, the factors that reduce the thermal conductivity of silicon nitride are clarified and the potential approaches to realize high thermal conductivity are described. Then, the recent achievements on the silicon nitride fabricated through the reaction bonding and post sintering technique are presented. Because of a smaller amount of impurity oxygen, the obtained thermal conductivity is substantially higher, compared to that of the conventional gas-pressure sintered silicon nitride, while the microstructures and bending strengths are similar to each other between these two samples. Moreover, further improvement of the thermal conductivity is possible by increasing ${\beta}/{\alpha}$ phase ratio of the nitrided sample, resulting in a very high thermal conductivity of 177 W/($m{\cdot}K$) as well as a high fracture toughness of 11.2 $MPa{\cdot}m^{1/2}$.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.307-307
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• 2012

In this study, we investigated that the resistance switching characteristics of Al-doped MgOx films with increasing Al doping concentration and increasing film thickness. The Al-doped MgOx based ReRAM devices with a TiN/Al-doped MgOx/Pt/Ti/SiO2 were fabricated on Si substrates. The 5 nm, 10 nm, and 15 nm thick Al-doped MgOx films were deposited by reactive dc magnetron co-sputtering at $300^{\circ}C$ and oxygen partial ratio of 60% (Ar: 16 sccm, O2: 24 sccm). Micro-structure of Al-doped MgOx films and atomic concentration were investigated by XRD and XPS, respectively. The Al-doped MgOx films showed set/reset resistance switching behavior at various Al doping concentrations. The process voltage of forming/set is decreased and whereas the initial current level is increased with decreasing thickness of Al-doped MgOx films. Besides, the initial current of Al-doped MgOx films is increased with increasing Al doping concentration in MgOx films. The change of resistance switching behavior depending on doping concentration was discussed in terms of concentration of non-lattice oxygen of Al-doped MgOx.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.1
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• pp.44-50
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• 2018

The improved high-performance Fe-based perovskite-type oxides ($La_{0.7}Sr_{0.3}M_xFe_{1-x}O_3$, M = Cu, Cr, Ni) were synthesized by a citrate method and characterized by SEM, EDS, XRD and NMR spectroscopy analyses. The characterization analyses revealed that the stoichiometric amounts of lattice oxygen were existed in all of perovskite samples except for a nickel-doped perovskite. Fe-based perovskites exhibited a surprising result for ortho-para $H_2$ spin conversion reaction, indicating two orders of magnitude higher conversions and conversion rates than commercial $Fe_2O_3$. It was considered that this conversion difference might be attributed to the presence of oxygen vacancies in Fe-based perovskites prepared in this study.

• Journal of Sensor Science and Technology
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• v.11 no.6
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• pp.371-377
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• 2002

$Y_2O_3:Eu^{3+}$ and Li-doped $Y_2O_3:Eu^{3+}$ thin films have been grown on sapphire substrates using a pulsed laser deposition technique. The thin film phosphors were deposited at a substrate temperature of $600^{\circ}C$ under the oxygen pressure of 100, 200 and 300 mTorr. The films grown under different deposition conditions have been characterized using microstructural and luminescent measurements. The crystallinity and photoluminescence (PL) of the films are highly dependent on the oxygen pressure. The PL brightness data obtained from $Y_2O_3:Eu^{3+}$ films grown under optimized conditions have indicated that sapphire is one of the most promising substrate for the growth of high quality $Y_2O_3:Eu^{3+}$ thin film red phosphor. In particular, the incorporation of $Li^{+}$ ions into $Y_2O_3$ lattice could induce a remarkable increase of PL. The highest emission intensity was observed with LiF-doped $Y_{1.84}Li_{0.08}Eu_{0.08}O_3(Y_2O_3LiEu)$, whose brightness was increased by a factor of 2.7 in comparison with that of $Y_2O_3:Eu^{3+}$ films. This phosphor may promise for application to the flat panel displays.

• Korean Journal of Materials Research
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• v.11 no.11
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• pp.997-1000
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• 2001

Conducting perovskite oxide, $(Ba,Sr)RuO_3(BSR)$, which has many advantages for $(Ba,Sr)TiO_3(BST)$ due to their similarity in crystal structure, lattice constant and chemical composition, was prepared on n-type Si (100) by liquid delivery metalorganic chemical vapor deposition(LDMOCVD). The deposition characteristics of BSR were controlled by gas-phase mass-transfer in the experiment. The BSR films deposited at 50$0^{\circ}C$ and oxygen flow rate of 100 sccm(standard cc/min) showed an average roughness of 22 $\AA$and resistivity of 810 $\mu$$\Omega$-cm. The roughness of BSR films with oxygen flow rate showed a close relationship with the resistivity of films. BSR (110) peak shifted toward lower Bragg angle with increase of x in the$(Ba_x,Sr_{1-x})TiO_3$. The resistivity of BSR films increased from 810 to 924 $\mu$$\Omega$-cm with increase of Ba content(x).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1995.11a
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• pp.167-170
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• 1995

LiCoO$_2$is a electrode material of Li ion Cell which is expected as the cell with a very high electric charge density. The recent study is mainly to focused on a high power secondary cell. If very thin Li ion Cell can be made in the scale of IC substrate it can be a electric souse in IC chip , micro machine or very thin electrical display etc. LiCoO$_2$thin film can be made by CVD, Laser ablation, E-Beam, ton Beam process, sputtering etc. But to make the material with a high quality for a cell is difficult as the electrode in cell have the fitable ratio in components and a lattice structure of bulk etc. In this study, LiCoO$_2$is made by R.F magnetron sputtering with the variance of substrate temperature and oxygen partial pressure etc. In the substrate temperature of 600$^{\circ}C$ and the oxygen rate of 10%, we can acquire the good thin film LiCoO$_2$compared wish a bulk material.

• Journal of the Korean Ceramic Society
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• v.27 no.3
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• pp.299-310
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• 1990

The fabrication of Y-Ba-Cu-O films and experimental factors affecting to characteristics of films are studied in detail. Superconducting thick films are fabricated by the screen printing method. The metal-citrate precursors are obtained simply by mixing of metal nitrate with citric acid. The particle size of heat treated powders is approximately 0.3-1${\mu}{\textrm}{m}$ and the thickness of film is estimated as 30-35${\mu}{\textrm}{m}$. According to the XRD analysis, the films sintered at 870-93$0^{\circ}C$ for 10min. -6hr with P(oxygen)=1atm has the unique orthorhombic crystal symmetry indicating the 123 phae. Tc, onset is determined around 92-87。K, but it shows semiconducting behavior probably due to the oxygen deficiency in the lattice, porosity and impurities in films. Extrapolated Tc, zero is estimated as 76-50。K. For films sintered at 90$0^{\circ}C$ for 1hr, superconducting properties are observed with the room temperature resistivity of 0.025$\Omega$.cm Tc, onset at 88。K and Tc, zero at 63。K.

• Transactions of the Korean hydrogen and new energy society
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• v.14 no.4
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• pp.298-304
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• 2003

The thermal behavior of $NiFe_2O_4$ prepared by a solid-state reaction was investigated for $H_2$ generation by the thermochemical cycle. The reduction of $NiFe_2O_4$ started from $800^{\circ}C$, and the weight loss was 0.2-0.3 wt% up to $1000^{\circ}C$. In the $H_2O$ decomposition reaction, $H_2$ was generated by oxidation of reduced $NiFe_2O_4$. The crystal structure of $NiFe_2O_4$ maintained during the redox reaction of 5 cycles. From this observation, the lattice oxygen in $NiFe_2O_4$ is released without the structural change during the thermal reduction and oxygen deficient $NiFe_2O_4$ can be restored to the spinel structure of $NiFe_2O_4$.

• The Korean Journal of Ceramics
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• v.5 no.4
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• pp.371-374
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• 1999

Y2O3 and Nb2O5 co-doped tetragonal zirconia polycrystals((Y, Nb)-TZP) containing 10 to 30 vol% $Al_2O_3$ were prepared and hydrothermal stability of the composites was evaluated after aging for 5 h at the temperature range of $150^{\circ}C$ $250^{\circ}C$ under 4 MPa $H_2O$ vapor pressure in an autoclave. The (Y, Nb)-TZP/Al2O3 composites showed excellent phase stability under the hydrothermal conditions, as compared with the 3Y-TZP/$Al_2O_3$ composites, due to the combined effects of the Y-Nb ordering in the $t-ZrO_2$ lattice, the reduction of oxygen vacancy concentration, and the $Al_2O_3$ addition. The strength and fracture toughness of the (Y, Nb)-TZP/$Al_2O_3$ composite, containing 20 vol% of 2.8 $Al_2O_3$ particles, were 700 MPa and 8.1 MP.$am^{1/2}$, respectively.

• Progress in Superconductivity
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• v.13 no.3
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• pp.178-183
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• 2012

Two $RuSr_2(EuCe)Cu_2O_z$ samples (as prepared and after $N_2$ treatment) have been investigated by thermogravimetric (TC) analysis, high-resolution x-ray powder diffraction and magnetization measurements. TG measurements which were carried out in $H_2/Ar$ atmosphere showed that the $N_2$ treatment of the as-prepared sample at $650^{\circ}C$ for 2h leads to a decrease in the oxygen content z by about 0.25. This oxygen depletion was accompanied by an increase in the magnetic transition temperature from 54.0 K to 114.9 K. This magnetic behavior is discussed in connection with the results of Rietveld analysis of the x-ray diffraction data which showed that the $N_2$ treatment resulted in both a significant increase in the rotation angle of the $RuO_6$ octahedra and a decrease in c-lattice parameter of the sample.