• 한국분말재료학회지
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• 제28권2호
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• pp.143-149
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• 2021

In this study, (GaN)_1-x(ZnO)_x solid solution nanoparticles with a high zinc content are prepared by ultrasonic spray pyrolysis and subsequent nitridation. The structure and morphology of the samples are investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The characterization results show a phase transition from the Zn and Ga-based oxides (ZnO or ZnGa₂O₄) to a (GaN)_1-x(ZnO)_x solid solution under an NH3 atmosphere. The effect of the precursor solution concentration and nitridation temperature on the final products are systematically investigated to obtain (GaN)_1-x(ZnO)_x nanoparticles with a high Zn concentration. It is confirmed that the powder synthesized from the solution in which the ratio of Zn and Ga was set to 0.8:0.2, as the initial precursor composition was composed of about 0.8-mole fraction of Zn, similar to the initially set one, through nitriding treatment at 700℃. Besides, the synthesized nanoparticles exhibited the typical XRD pattern of (GaN)_1-x(ZnO)_x, and a strong absorption of visible light with a bandgap energy of approximately 2.78 eV, confirming their potential use as a hydrogen production photocatalyst.

• 폴리머
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• 제29권6호
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• pp.575-580
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• 2005

하이드록시 말단의 지방족 고차가지구조 폴리에스테르를 용융축합법을 이용하여 합성하였다. 말단의 하이드록시 그룹을 acryloyl chloride를 사용하여 비닐 말단으로 변환시켰으며, 말단변화에 따른 구조를 분석하고 분자량을 측정하였다. 비닐 말단의 지방족 고차가지구조 폴리에스테르는 점도가 높고 노란색의 투명한 액체이며, 하이드록시 말단의 지방족 고차가지구조 폴리에스테르에 비해 유리전이온도가 낮았다. 또한 비닐 말단으로 변형한 후에는 열안정성이 감소하였으며, 말단 작용기의 전환율 차이에 의해 불규칙적인 열분해거동을 보였다.

• 한국세라믹학회지
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• 제37권5호
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• pp.466-472
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• 2000

As cathode materials of LiMn2O4-based lithium-ion secondary batteries, Li(Mn1-$\delta$M$\delta$)2O4 (M=Ni and Co, $\delta$=0, 0.05, 0.1 and 0.2) materials which Co and Ni are substituted for Mn, were syntehsized by the solid state reaction at 80$0^{\circ}C$ for 48 hours. No second phases were formed in Li(Mn1-$\delta$M$\delta$)2O4 system with substitution of Co. However, substitution of Ni caued to form a second phase of NiO when its composition exceeded over 0.2 of $\delta$ in Li(Mn1-$\delta$M$\delta$)2O4. As the results of charging-discharging test, the maximum capacity of Li(Mn1-$\delta$M$\delta$)2O4 appeared in $\delta$=0.1 for both Co and Ni. Also, Li(Mn1-$\delta$M$\delta$)2O4 electrode showed higher capacity and better cycle performance than LiMn2O4.

• 한국재료학회지
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• 제3권4호
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• pp.422-423
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• 1993

이 short note에서 우리는 bulk gadolinium의 강자성에서 상자성으로의 전이온도(즉, Curie점) 측정에 대한 결과를 보고하고자 한다. 이 결과보고는 gadolinium박막에 대한 이전의 결과에 정당성을 주기 위해서 쓰여졌다. 본 실험에서 bulk gadolinium의 Curie점은 시료의 저항을 온도의 함수로 측정함으로써 결정하였다. 이는 Curie점에서 비열의 특이성이 바로 비저항의 특이성으로 연결되기 때문이다. 결과적으로 우리는 bulk gadolinium의 Curie점이 19.2${\pm}$0.$3^{\circ}C$가 되고이 값은 비열의 실험치로 결정한 다른 그룹들의 실험값들과 잘 일치하고 있음을 알 수 있었다.

• 한국세라믹학회지
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• 제33권12호
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• pp.1301-1310
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• 1996

Generally it requires high sintering temperatures more than 135$0^{\circ}C$ to make semiconductive BaTiO3 ceramics. Also it is very difficult to achieve a homogeneous mixing in solid-state reaction method. Therefore the liquid phase distributed to non-uniform dilute the characteristics of PTCR. In order to improve the uniformity this study is used the sol-gel coating method. Using this method we studied the new manufacturing process that had a high reproducibility and mass production capability. Tetraethyl orthosilicate (TEOS) was used as a source of Si. The semiconductive BaTiO3 ceramics which was produced by sol-gel method for the SiO2 addition and sintered between 124$0^{\circ}C$ and 130$0^{\circ}C$ showed almost same resistivity at room temperature among 125$0^{\circ}C$ and 130$0^{\circ}C$. As the results We could be sintered the semiconducting BaTiO3 ceramics at lower temperature even at 125$0^{\circ}C$ maintaining the same specific resistivity ratio ($\rho$max/$\rho$min) at 130$0^{\circ}C$. The specific resistivity both below and above the Curie temperature were increased by slow cooling and the steepness of the plots in the reasion of transition from low to high resistance increased as the cooling rate decreased.

• 한국전기전자재료학회논문지
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• 제14권7호
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• pp.562-566
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• 2001

The effects of MnO$_2$ addition on the properties in Pb(Mg$_{1}$3/Nb$_{2}$3/)O$_3$ relaxor ferroelectrics were studied in the phase transition temperature range from -4$0^{\circ}C$ to 11$0^{\circ}C$. Specimens were made via solid state processing method. Dielectric properties, piezoelctric properties, electric-field-induced strain were examined to clarify the effect of MnO$_2$ addition in 0.9MN-0.1PT. As the amount of MnO$_2$ increases, the maximum dielectric constant and the dielectric loss decreases. Q$_{m}$ increased by increasing the doping contents of Mn. When 0.5wt% MnO$_2$ was doped, Q$_{m}$ increased from 95 to 480. The electric-filed-induced strain and polarization decreases as the amount of MnO$_2$ increases. From the experimental results, it was suggested that Mn behaves as an ferroelectric domain pinning element.ent.

• 한국재료학회지
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• 제26권11호
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• pp.623-627
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• 2016

$La_{1-x}Ba_xMnO_3$ (x = 0.30, 0.35 and 0.40) samples have been prepared by solid-state reaction method. The X-ray diffraction (XRD) study showed that all the samples crystallized in a rhombohedral structure with an R-3c space group. Variation of the magnetization as a function of the temperature and applied magnetic field was carried out. All the samples revealed ferromagnetic to paramagnetic (FM-PM) phase transition at the Curie temperature $T_C{\sim}342K$. The magnetic entropy change was also studied through examination of the measured magnetic isotherms M(H, T) near $T_C$. The magnetocaloric effect was calculated in terms of the isothermal magnetic entropy change. The maximum entropy change reaches a value of 1.192 J/kgK under a magnetic field change of 2.5T for the $La_{0.6}Ba_{0.4}MnO_3$ composition. The relative cooling power (RCP) is 79.31 J/kg for the same applied magnetic field.

• Macromolecular Research
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• 제13권3호
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• pp.243-252
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• 2005

The effect of the vinyl acetate (VA) content on the thermal, viscoelastic, rheological, morphological and mechanical behaviors in various blends of ethylene-vinyl acetate (EVA)/ethylene-$\alpha$-olefin copolymers was investigated using 28, 22 and $15 mol\%$ of VA in EVA. In the DSC melting and crystallization thermograms of all of the EVA systems blended with ethylene-$\alpha$-olefin copolymers, discrete peaks were observed which were related to the constituents. In the dynamic mechanical thermal analysis, the storage modulus increased with increasing content of ethylene-$\alpha$-olefin copolymers. In addition, the transition regions relating to the tan bpeaks varied with the VA content. The crossover point between G' and G" varied depending on the VA contents, and shear-thinning was more prominent in the EVA/EtBC system. In the SEM investigation, a discrete phase morphology was observed in both the EVA/EtBC and EVA/EtOC blends, but the contrast improved with decreasing VA content. However, the tensile strength and modulus improved, but the elongation at break reduced with decreasing VA content, implying that the ethylene-$\alpha$-olefin copolymers play the role of reinforcing materials. Thus, the EVA and ethylene-$\alpha$-olefin components in the copolymers are immiscible in the molten and solid states, but are nevertheless mechanically compatible.

• 한국재료학회지
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• 제30권3호
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• pp.136-141
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• 2020

The magnetocaloric effect (MCE), which is the reversible temperature change of magnetic materials due to an applied magnetic field, occurs largely in the vicinity of the magnetic phase transition temperature. This phenomenon can be used to induce magnetic refrigeration, a viable, energy-efficient solid-state cooling technology. Recently, Metal-organic frameworks (MOFs), due to their structural diversity of tunable crystalline pore structure and chemical functionality, have been studied as good candidates for magnetic refrigeration materials in the cryogenic region. In cryogenic cooling applications, MCE using MOF can have great potential, and is even considered comparable to conventional lanthanum alloys and magnetic nanoparticles. Owing to the presence of large internal pores, however, MOF also exhibits the drawback of low magnetic density. To overcome this problem, therefore, recent reports in literature that achieve high magnetic entropy change using a dense structure formation and ligand tuning are introduced.

• 한국전기전자재료학회논문지
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• 제17권2호
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• pp.236-241
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• 2004

New electrolytes of cubic L $a_2$M $o_2$-x Nbx $O_{9-}$$\delta$/(x=0, 0.05, 0.1, 0.2) were fabricated by a solid-state reaction method and their sintered densities were approximately 93％ of theoretical density. X-ray diffraction analysis and microstructure observation for the sintered specimens were performed. The at complex impedance were measured at 34$0^{\circ}C$ to 93$0^{\circ}C$ in air and fitted with a Solatron ZView program. Their impedance spectra showed big difference below and over the phase transition temperature (58$0^{\circ}C$). The electrical conductivity of L $a_2$M $o_2$ $O_{9}$ was 1.36${\times}$10$^{-2}$ S$cm^{-1}$ / at 817$^{\circ}C$. Comparing to undoped L $a_2$M $o_2$ $O_{9}$ , Nb-doped specimen showed the increase of electrical conductivity due to the aliovalent doping effect..