• Journal of the Korean Ceramic Society
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• v.34 no.12
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• pp.1247-1253
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• 1997

Sinter-active yttria powders were prepared by a solution precipitation with using a self-decomposing precipitation agent NH2CONH2(urea). The cold-pressed powders can be sintered to full density and the microstructure of grains less than 200 nm at a temperature as low as 120$0^{\circ}C$. The activity of the yttria powder has been controlled by varying nucleation conditions during precipitation and by minimizing formation of aggregates. The type of precursor is decisive in preparation of a sinter-active oxide powder, and urea is desirable as a precipitation agent for an active yttrium oxide powder.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.13 no.6
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• pp.309-314
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• 2003

A spark plasma sintering technique has been used for the fabrication of $Al_2O_3$-SiC nanocomposites at the low temperature of $1100^{\circ}C$∼$1500^{\circ}C$. The sintered $Al_2O_3$-SiC composites shows very homogeneous microstructure without any particular abnormal grain growth, indicating that the addition of nano-sized SiC particles is very effective to control grain growth and to induce the residual stress in the $Al_2O_3$ matrix, resulting in the intragranular fracture. These SiC particles are present in the grain boundaries and also intragrain, depending on the sintering condition, and improve remarkably the mechanical properties of $Al_2O_3$-SiC composite through the mechanisms of strengthening and toughening induced by crack diffraction and crack bridging.

• Journal of the Korean Ceramic Society
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• v.40 no.6
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• pp.560-565
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• 2003

M-doped (M=Al, Ni) ZnO thermoelectric materials were fully densified at low temperatures of 800∼1,000$^{\circ}C$ and their sintering characteristics and microstructural features were investigated. Electron microscopic analysis showed that the addition of NiO promoted tile formation of solid solution and caused actively grain growth. The addition of A1$_2$O$_3$ prevented the evaporation of pure ZnO at grain boundaries and suppressed the grain growth by the formation of secondary phase. In case of the addition of A1$_2$O$_3$ together with NiO, the specimen showed an excellent microstructure and also the SEM-EBSP (Electron Back-scattered Diffraction Pattern) analysis confirmed that it shows a superior grain boundary distribution to the others specimens. These microstructural characteristics induced by the addition of A1$_2$O$_3$ together with NiO may increase the electrical conductivity by the increase in carrier concentration and decrease the thermal conductivity by the phonon scattering effect and, consequently, improve the thermoelectric property.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.5
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• pp.995-999
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• 2007

The lead zirconate titanate (PZT) powders were synthesized to make the piezoelectric ceramics in low temperature as low as $900^{\circ}C$. To investigate the influence of additives on sintering of PZT, two kinds of sintering aids were made as follows; $wB_2O_3-xBi_2O_3-zCuO$and LiBiO2-CuO. The sintering aid, $1{\sim}3$ wt.% $LiBiO_2-CuO$, was added into these PZT powders and the specimens were fired at temperature in the range of $800{\sim}1200^{\circ}C$. The highest density was shown in the specimen with 1 wt.% $LiBiO_2-CuO$ as additive at temperature of $900^{\circ}C$. The sintered specimen were analyzed by X-ray diffraction(XRD) and scanning electron microscopy (SEM) was utilized to observe the microstructure, especially the densified morphology of specimens. In the XRD pattern, the well-crystallized PZT phase could be obtained in consequence of firing at $900^{\circ}C$. The scanning electron microscopy(SEM) was utilized to observe the structure of specimens after firing at $900^{\circ}C$. The densified perovskite structure of $PbZrTiO_3$ could be obtained by sintering at temperature as low as $900^{\circ}C$. The high sinterability of PZT ceramics was attributed to the low formation temperature of the liquid phase of additives.

• Journal of Powder Materials
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• v.27 no.1
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• pp.52-57
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• 2020

In this study, we report the microstructure and characterization of Ta₂₀Nb₂₀V₂₀W₂₀Ti₂₀ high-entropy alloy powders and sintered samples. The effects of milling time on the microstructure and mechanical properties were investigated in detail. Microstructure and structural characterization were performed by scanning electron microscopy and X-ray diffraction. The mechanical properties of the sintered samples were analyzed through a compressive test at room temperature with a strain rate of 1 × 10^-4 s^-1. The microstructure of sintered Ta₂₀Nb₂₀V₂₀W₂₀Ti₂₀ high-entropy alloy is composed of a BCC phase and a TiO phase. A better combination of compressive strength and strain was achieved by using prealloyed Ta₂₀Nb₂₀V₂₀W₂₀Ti₂₀ powder with low oxygen content. The results suggest that the oxide formed during the sintering process affects the mechanical properties of Ta₂₀Nb₂₀V₂₀W₂₀Ti₂₀ high-entropy alloys, which are related to the interfacial stability between the BCC matrix and TiO phase.

• Journal of Powder Materials
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• v.30 no.5
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• pp.394-401
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• 2023

Li_1.5Al_0.5Ti_1.5(PO₄)₃ (LATP) is considered to be one of the promising solid-state electrolytes owing to its excellent chemical and thermal stability, wide potential range (~5.0 V), and high ionic conductivity (~10^-4 S/cm). LATP powders are typically prepared via the sol-gel method by adding and mixing nitrate or alkoxide precursors with chelating agents. Here, the thermal properties, crystallinity, density, particle size, and distribution of LATP powders based on chelating agents (citric acid, acetylacetone, EDTA) are compared to find the optimal conditions for densely sintered LATP with high purity. In addition, the three types of LATP powders are utilized to prepare sintered solid electrolytes and observe the microstructure changes during the sintering process. The pyrolysis onset temperature and crystallization temperature of the powder samples are in the order AC-LATP > CA-LATP > ED-LATP, and the LATP powder utilizing citric acid exhibits the highest purity, as no secondary phase other than LiTi₂PO₄ phase is observed. LATP with citric acid and acetylacetone has a value close to the theoretical density (2.8 g/cm³) after sintering. In comparison, LATP with EDTA has a low sintered density (2.2 g/cm³) because of the generation of many pores after sintering.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.646-649
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• 2002

The microwave dielectric properties and the structure of $Sb_2O_5$ modified $BiNb_xSb_{1-x}O_4$ ceramics were investigated. The structure of these ceramics were orthohombic phase at all sintering temperatures and there were not the second phase. These ceramics added sintering additive such as CuO and $V_2O_5$ were sinterable at a low temperature$(880^{\circ}C{\sim}960^{\circ}C)$ by liquid phase. Dielectric properties of $BiNb_xSb_{1-x}O_4$ ceramics were also improved than these of $BiNbO_4$ ceramics. The content of modified atom controlled the microstructure, dielectric constant and quality factor. As a result, We could obtain following result; ${\varepsilon}r$=42~44, $Q{\cdot}f_0$=20,000~42,000GHz, $\tau_f=-7{\sim}-28ppm/^{\circ}C$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.34 no.5
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• pp.342-347
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• 2021

Phase evolution, sintering behavior, microstructure, and microwave dielectric properties of (1-x) mol Ba₃V₄O₁₃ - (x) mol BaV₂O₆ system were investigated. The sintered specimens of all compositions consisted of Ba₃V₄O₁₃ and BaV₂O₆, and no secondary phase was observed. As x increased, the linear shrinkage decreased to the composition of x=0.5, and then increased again, implying that Ba₃V₄O₁₃ and BaV₂O₆ phases interfered mutually with each other during sintering. All compositions showed a dense microstructure with a large grain growth. Cracks were observed in some compositions because of the relatively high sintering temperature of 620~640℃. As x increased, the dielectric constant increased, while the quality factor was maintained from about 50,000 GHz to about 70,000 GHz up to the composition of x=0.9, and then decreased to 20,987~27,180 GHz at the composition of x=1.0. As x increased, the temperature coefficient of the resonance frequency showed a (+) value from a (-) value. The dielectric constant, the quality factor, and the temperature coefficient of resonant frequency of x=0.7 composition sintered at 640℃ for 4 hours were 10.61, 71,126 GHz, and -4.9 ppm/℃, respectively. This composition showed a good chemical compatibility with Al powder, indicating that the Ba₃V₄O₁₃-BaV₂O₆ ceramics are a candidate material for ULTCC (Ultra-Low Temperature Co-fired Ceramics) applications.

• Journal of the Korean Ceramic Society
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• v.41 no.2
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• pp.165-169
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• 2004

Microwave dielectric properties and the behavior of low-temperature sintering of $Zn_{1-x}(Li_{1/2}La_{1/2})_xTiO_3$ ($0.01{\leq}x{\leq}0.05$) with 4 wt% $H_3BO_3$ were investigated as a function of $(Li_{1/2}La_{1/2})^{2+}$ content. The sintering temperature of the specimens can be reduced from $1150^{\circ}C$ to $875^{\circ}C$ with the addition of 4 wt% $H_3BO_3$ as a sintering agent. Dielectric constant (K) and Temperature Coefficient of resonant Frequency (TCF) with the substitution of ($(Li_{1/2}La_{1/2})^{2+}$ ion depended on dielectric mixing rule. Quality factor (Qf) depended on density and microstructure. Typically, K of 26.5, Qf of 19,030 GHz and TCF of 7.5 ppm$/^{\circ}C$ were obtained for the specimens with x=0.03 sintered at $875^{\circ}C$ for 3 h.

• Journal of the Korean Ceramic Society
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• v.41 no.12 s.271
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• pp.884-888
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• 2004

Effects of NiO were studied in aspects of dielectric properties and microstructure of $0.96(0.91Pb(Mg_{1/3}Nb_{2/3})O_3-0.09PbTiO_3)­0.04BaTiO_3$ (PMN-PT-BT, PBT). The PBT was prepared by a conventional mixed oxide method using $(MgCO_3)_4{\cdot}Mg(OH)_2$ instead of MgO through Lewis acid-base interaction. NiO was added in the range of 0.5 to $3.0\;wt\%$ as thermally decomposable $2NiCO_3{\cdot}3Ni(OH)_2$ and it seemed to enhance densification to a large extent below $1000^{\circ}C$. But all the systems gave rise to ceramics with almost same relative sintered density of 96% by sintering at $1000^{\circ}C$ for 2 h. But it turned out that the addition of NiO was detrimental to dielectric constant but beneficial to the loss of dielectric constant.