• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.49 no.9
• /
• pp.516-522
• /
• 2000

The mechanical and electrical properties of the hot-pressed and annealed $\beta-SiC-ZrB_2$ electroconductive ceramic composites were investigated as a function of the liquid forming additives of$Al_2O_3+Y_2O_3$ Phase analysis of composites by XRD revealed $\alpha-SiC(6H) ZrB_2\; and YAG(Al_5Y_3O_{12})$ The relative density of composites were increased with increased Al2O3+Y2O3 contents. The Flexural strength showed the highest value of 390.6MPa for composites added with 20wt% Al2O3+Y2O3 additives at room temperature. Owing to crack deflection crack bridging phase transition and YAG of fracture toughness mechanism the fracture toughness showed the highest value of 6.3MPa.m1/2 for composites added with 24wt% Al2O3+Y2O3 additives at room temperature. The resistance temperature coefficient showed the value of$ 2.46\times10^{-3}\;, 2.47\times10^{-3},\; 2.52\times10^{-3}/^{\circ}C$ for composite added with 16, 20, 24wt% Al2O3+Y2O3 additives respectively. The electrical resistivity of the composites was all positive temperature coefficient resistance(PTCR) in the temperature range of $256{\circ}C\; to\; 900^{\circ}C$.

• Proceedings of the KIEE Conference
• /
• 1997.07d
• /
• pp.1573-1576
• /
• 1997

Thin films of $BaTiO_3$ system were prepared by radio frequency (rf)/dc magnetron sputtering method. We have investigated crystal structure, surface morphology and PTCR(positive-temperature coefficient of resistance) characteristics of the specimen depending on second heat - treatment temperatures. Scanning electron microscope(SEM) image of $BaTiO_3$ thin films shows that the specimen heat treated in between 900 and 1100[$^{\circ}C$] shows a grain growth. At 1100[$^{\circ}C$], the specimen stops grain-growing and becomes a crystal. A resistivity-temperature characteristics of the specimen depends on the doping concentrations of Mn.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2000.07a
• /
• pp.839-842
• /
• 2000

The mechanical and electrical properties of the hot-pressed and annealed $\beta$-SiC-ZrB$_2$ electroconductive ceramic composites were investigated as function of the liquid forming additives of $Al_2$O$_3$+Y$_2$O$_3$. Phase analysis of composites by XRD revelled $\alpha$ -SiC(6H), ZrB$_2$, and YAG(Al$_{5}$ Y$_3$O$_{12}$ ). Owing to crack deflection, crack bridging, phase transition and YAG of fracture toughness mechanism, the fracture toughness showed the highest value of 6.3MPa.m$^{1}$2/ for composites added with 24wt% $Al_2$O$_3$+Y$_2$O$_3$additives at room temperature. The resistance temperature coefficient respectively showed the value of 2.46$\times$10$^{-3}$ , 2.47$\times$10$^{-3}$ , 2.52$\times$ 10$^{-3}$ $^{\circ}C$ for composite added with 16, 20, 24wt% A1$_2$O$_3$+Y$_2$O$_3$additives. The electircal resistivity of the composites was all positive temperature coefficient resistance(PTCR) in the temperature range of $25^{\circ}C$ to 90$0^{\circ}C$.

• Proceedings of the KIEE Conference
• /
• 1994.11a
• /
• pp.293-295
• /
• 1994

Barium Titanate ($BaTiO_3$) is one of the few titanateds which is cubic at room temperature. It has the perovskite structure, high dielectric constant (${\varepsilon}_r=300$) and a small temperature coefficient of resistance due to it's Low transition temperature ($Tc=120^{\circ}c$). PTCR (Positive Temperature Coefficient of Resistivity) thermistor in thin film $BaTiO_3$ system was prepared by using radio frequency (13.56MHz) and BC magnetron sputter equipment. Polycrystalline, and surface structure characteristics of the specimens were measured by X-ray diffraction (D-Max3, Rigaku, Japan), SEM(Scanning Electron Microscopy: M. JSM84 01, Japan), respectively. Temperature at below $600^{\circ}C$, $1000^{\circ}C$ to $700^{\circ}C$, and above $1100^{\circ}C$ for spotted $BaTiO_3$ thin films showed the amorphous, degree of crystal growth, and polycrystalline, respectively.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.53 no.7
• /
• pp.352-357
• /
• 2004

The composites were fabricated, respectively, using 61vol.% SiC - 39vol.% TiB$_2$ and using 61vo1.% SiC - 39vo1.% WC powders with the liquid forming additives of 12wt% $Al_2$O$_3$＋Y$_2$O$_3$ by pressureless annealing at 180$0^{\circ}C$ for 4 hours. Reactions between SiC and transition metal TiB$_2$, WC were not observed in this microstructure. The result of phase analysis of composites by XRD revealed SiC(6H), TiB$_2$ and YAG(Al$_{5}$Y$_3$O$_{12}$) crystal phase on the SiC-TiB$_2$, and SiC(2H), WC and YAG(Al$_{5}$Y$_3$O$_{12}$) crystal phase on the SiC-WC composites. $\beta$\$\longrightarrow$$\alpha$-SiC phase transformation was ocurred on the SiC-TiB$_2$, but $\alpha$\$\longrightarrow$$\beta$-SiC reverse transformation was not occurred on the SiC-WC composites. The relative density, the vicker's hardness, the flexural strength and the fracture toughness showed respectively value of 96.2%, 13.34GPa, 310.19Mpa and 5.53Mpaㆍml/2 in SiC-WC composites. The electrical resistivity of the SiC-TiB$_2$ and the SiC-WC composites is all positive temperature coefficient resistance(PTCR) in the temperature ranges from $25^{\circ}C$ to 50$0^{\circ}C$. 2.64${\times}$10-2/$^{\circ}C$ of PTCR of SiC-WC was higher than 1.645${\times}$10-3/$^{\circ}C$ of SiC-TiB$_2$ composites.posites.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2000.04b
• /
• pp.72-75
• /
• 2000

The effect of $Al_2O_3+Y_2O_3$ additives on fracture toughness of ${\beta}-SiC-TiB_2$ composites by hot-pressed sintering were investigated, The ${\beta}-SiC-TiB_2$ ceramic composites were hot-presse sintered and annealed by adding 4, 8, 12wt% $Al_2O_3+Y_2O_3$(6 : 4wt%) powder as a liquid forming additives at low temperature($1800^{\circ}C$) for 4h. In this microstructures, the relative density is over 97% of the theoretical density and the porosity increased with increasing $Al_2O_3+Y_2O_3$ contents because of the increasing tendency of pore formation. But the fracture toughness showed the highest of $7.0MPa{\cdot}m^{1/2}$ for composites added with 12wt% $Al_2O_3+Y_2O_3$ additives at room temperature. The electrical resistivity showed the lowest of $1.59\times10^{-3}\Omega{\cdot}cm$ for composite added with 8wt% $Al_2O_3+Y_2O_3$ additives at room temperature and is all positive temperature coefficient resistance(PTCR} against temperature up to $700^{\circ}C$.

• Proceedings of the KIEE Conference
• /
• 2000.07c
• /
• pp.1545-1547
• /
• 2000

The mechanical and electrical properties of the hot-pressed and annealed $\beta$-Sic-$TiB_2$ electroconductive ceramic composites were investigated as function of the liquid forming additives of $Al_{2}O_{3}+Y_{2}O_3$. Phase analysis of composites by XRD revealed $\alpha$-SiC(6H), $TiB_2$, and YAG($Al_{5}Y_{3}O_{12}$). The relative density and the mechanical properties of composites were increased with increasing $Al_{2}O_{3}+Y_{2}O_3$ contents because YAG of reaction between $Al_{2}O_3$ and $Y_{2}O_3$ was increased. The Flexural strength showed the highest value of 432.5MPa for composites added with l2wt% $Al_{2}O_{3}+Y_{2}O_3$ additives at room temperature. Owing to crack deflection, crack bridging, phase transition and YAG of fracture toughness mechanism. the fracture toughness showed 7.1MPa${\cdot}m^{1/2}$. For composites added with l2wt% $Al_{2}O_{3}+Y_{2}O_3$ additives at room temperature The electrical resistivity and the resistance temperature coefficient respectively showed the lowest of 6.0${\sim}10^{-4}{\Omega}{\cdot}$ cm and 3.1${\times}10^{-3}/^{\circ}C$ for composite added with l2wt% $Al_{2}O_{3}+Y_{2}O_3$ additives at room temperature. The electrical resistivity of the composites was all positive temperature coefficient resistance(PTCR) in the temperature range of 25$^{\circ}C$ to 700$^{\circ}C$.

• Proceedings of the KIEE Conference
• /
• 2007.07a
• /
• pp.1303-1304
• /
• 2007

The composites were fabricated, respectively, using 61[vol.%]SiC-39[vol.%]$TiB_2$ and using 61[vol.%]SiC-39[vol.%]$ZrB_2$ powders with the liquid forming additives of 12[wt%] $Al_{2}O_{3}+Y_{2}O_{3}$ by hot pressing annealing at $1650[^{\circ}C]$ for 4 hours. Reactions between SiC and transition metal $TiB_2$, $ZrB_2$ were not observed in this microstructure. ${\beta}{\rightarrow}{\alpha}$-SiC phase transformation was occurred on the SiC-$TiB_2$ and SiC-$ZrB_2$ composite. The relative density, the flexural strength and Young's modulus showed the highest value of 98.57[%], 226.06[Mpa] and 86.38[Gpa] in SiC-$ZrB_2$ composite at room temperature respectively. The electrical resistivity showed the lowest value of $7.96{\times}10^{-4}[{\Omega}{\cdot}cm]$ for SiC-$ZrB_2$ composite at $25[^{\circ}C]$. The electrical resistivity of the SiC-$TiB_2$ and SiC-$ZrB_2$ composite was all positive temperature coefficient resistance (PTCR) in the temperature ranges from $25[^{\circ}C]$ to $700[^{\circ}C]$. The resistance temperature coefficient of composite showed the value of $6.88{\times}10^{-3}/[^{\circ}C]$ and $3.57{\times}10^{-3}/[^{\circ}C]$ for SiC-$ZrB_2$ and SiC-$TiB_2$ composite in the temperature ranges from $25[^{\circ}C]$ to $700[^{\circ}C]$.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.48 no.2
• /
• pp.92-97
• /
• 1999

The mechanical and electrical properties of the hot-pressed and annealed $\beta-Sic$+39vol.%$ZrB_2$ electroconductive ceramic composites were investigated as a function of the liquid forming additives of $Al_2O_3+Y_2O_3(6:4wt%)$. In this microstructures, no reactions and elongated $\alpha$-SiC grains with equiaxed $ZrB_2$, gains were observed between $\beta-SiC$ and $ZrB_2$, and the relative density was over 97.6% of the theoretical density. Phase analysis of the composites by XRD revealedmostly of $\alpha$-SiC(6H, 4H), $ZrB_2$, and weakly $\beta-SiC$(15R) phase. The fracture toughness decreased with increasing $Al_2O_3+Y_2O_3$ contents and showed the highest of $6.37MPa.m^{\fraction ane-half}$ for composite added with 4wt% $Al_2O_3+Y_2O_3$ additives at room temperature. The electrical resistivity increased with increasing $Al_2O_3+Y_2O_3$contents and showed the lowest of $1.51\times10^{-4}\Omega.cm$ for composite added with $Al_2O_3+Y_2O_3$ additives at $25^{\circ}C$. This reason is the increasing tendency of pore formation according to amount of liquid forming additives $Al_2O_3+Y_2O_3$. The electrical resistivity of the composites was all positive temperature coefficient resistance(PTCR) against temperature up to $700^{\circ}C$.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.9 no.5
• /
• pp.498-503
• /
• 1999

La-doped $BaTiO_3$ ceramics were prepared from BaTiO(C_2O_4)_2\;{\cdot}\;XH_2O(BTO)$, which was synthesized by homogeneous precipitation using dimethyl oxalate. The electrical properties of La-doped $BaTiO_3$ were investigated with variation of La-contents and particle size. It was found that a large PTCR (positive temperature coefficient of resistivity) effect was appeared in the conditions at the 0.6 mol% of La-content and at small particle size of BTO as 1.0$\mu\textrm{m}$. The plot of temperature vs. 1/$\varepsilon_m$(T) above Curie temperature $(T_c)$ was agreed with Curie-Weiss law. The potential barrier calculated from measured resistance and capacitance of specimen, also gave higher value at small particle size of BTO as 1.0 $\mu\textrm{m}$ and at La-content of 0.6 mol%.