• Journal of the Korean Ceramic Society
• /
• v.28 no.5
• /
• pp.406-414
• /
• 1991

The composition of base glass was selected as MgO 8, Al2O3 24, SiO2 68 in weight percent. TiO2 and ZrO2 were added to the base glass to investigate their effects as nucleating agents. In the case of ZrO2 addition, the optimum temperature for nucleation, which was related to the precipitation of tetragonal ZrO2, was 80$0^{\circ}C$. The optimum growth condition for the crystal was 87$0^{\circ}C$ for 8 hrs, and the major crystal phases precipitated in the samples were $\beta$-quartz ss. and mullite. The light transmissivity turned out to be around 80 per cent. On the other hand, when the TiO2 was added, it was difficult to determine the nucleating temperature, because the samples turned easily into translucency during the heat treatment. Therefore, it was almost impossible to retain transparency in the samples. The light transmissivity was below 30 per cent.

• Korean Journal of Materials Research
• /
• v.5 no.1
• /
• pp.36-41
• /
• 1995

Dielectric properties were investigated at Mn doped $(Pb_{1-x}Ca_{x})ZrO_{3}$ with x=0.38 in microwavefrequencies. Both the density and Q values of sintered ceramics increased with increasing calciningtemperature. In the sample sintered at $1300^{\circ}C$ for 2 hrs, the deped Mn ions completely solubled in $(Pb,Ca)ZrO_{3}$ phase until 0.5wt% and the grain size was independent of doping amount. It was observed thathigh dielectric constant of 90 - 100 and high quality factor of 1300 at 4 GHz for O.l5wt% Mn doped$(Pb_{0.62}Ca_{0.38})ZrO_{3}$. The Mn" and Mn" worked as acceptors in $(Pb,Ca)ZrO_{3}$ which created the oxygen vacancies and affected the increment of the Q values. However, the excess Mn doping more than 0.5wt% resulted in decreasing Q values.decreasing Q values.

• Journal of the Korean Ceramic Society
• /
• v.39 no.11
• /
• pp.1017-1022
• /
• 2002

$(Ba_{1-x}Ca_x)(Ti_{1-y}Zr_y)O_3(BCTZ)$ powders for the Ni-electrode Multilayer Ceramic Capacitor(MLCC) were synthesized via hydrothermal treatment using mixed aqueous solutions of $BaCl_2{\cdot}2H_2O,\Ca(NO_3)2{\cdot}4H_2O,\ ZrOCl_2{\cdot}8H_2O$ and $TiCl_4$. Two component and three component systems were also extensively studied for basic data. BT, CT and BZ powders were crystalline but CZ was determined to be amorphous under the same synthetic condition. In BTZ system, Zr and Ti were completely soluble and Ca would be substituted for Ba up to ∼6 mol% in BCT. The submicron-sized $(Ba_{0.95}Ca_{0.05})(Ti_{0.80}Zr_{0.20})O_3$ powder of the target composition was successfully synthesized at $150{\circ}$ for 12h.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2001.11b
• /
• pp.42-45
• /
• 2001

$(Ba_{0.6}Sr_{0.4}Ca_{x})TiO_{3}+yZrO_{2}$ wt% (x=0.10, 0.15, 0.20, y=0.5~3.0) specimens were fabricated by the mixed-oxide method and then the structural and dielectric properties as a function of the composition ratio and $ZrO_2$ contents were studied. All BSCT specimens showed dense and homogeneous structure without the presence of the seconds phase. The Curie temperature and the dielectric constant at room temperature decreased with increasing the Ca/Ba composition ratio and $ZrO_2$ content. The BSCT(50/40/10) specimens showed the excellent tunability property. And the tunability were increased with increasing the contents of $ZrO_2$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2001.11a
• /
• pp.42-45
• /
• 2001

(Ba$_{0.6-x}$Sr$_{0.4}$Ca$_{x}$)TiO$_3$+yZrO$_2$wt% (x=1.10, 0.15, 0.20, y=0.5~3.0) specimens were fabricated by the mixed and ZrO$_2$ contents were studied. All BSCT specimens contents were studied. All BSCT specimens showed dense and homogeneous structure without the presence of the seconds phase. The Curie temperature and the dielectric constant at room temperature decreased with increasing the Ca/Ba composition ratio and ZrO$_2$ content. The BSCT(50/40/10) specimens showed the excellent tunability property. And the tunability were increased with increasing the contents of ZrO$_2$./TEX>.

• Journal of the Korean Ceramic Society
• /
• v.41 no.1
• /
• pp.1-8
• /
• 2004

The microstructural features and mechanical behavior of directionally solidified $(Y_2O_3)ZrO_2/Al_2O_3$ eutectic fibers after extended beat treatment in oxidizing environment were investigated. The fiber was grown continuously by an Edge-defined Film-fed Growth (EFG) technique. The microstructure was characterized using X-Ray Diffraction (XRD) and Scanning Electron Microscopy(SEM). The microstructure of the fiber in the as-fabricated state consists of highly oriented colonv and fine lamellar microstructure along the fiber axis. Tensile strength of the $(Y_2O_3)ZrO_2/Al_2O_3$ eutectic fiber remained unchanged with heat treatment at temperatures between $1200^{\circ}C$ and $1500^{\circ}C$ up to 300h. The weibulls modulus remained fairly constant after extended thermal exposure. The fracture toughness and crack propagation behavior were investigated. The fracture toughness ($K_{1C}$) of the $(Y_2O_3)ZrO_2/Al_2O_3$ eutectic fiber in the as-fabricated state were measured to be 3.6 ${\pm}$ 0.5 MPa${\cdot}m^{1/2}$ by an indentation technique and 2.2 ${\pm}$ 0.2 MPa${\cdot}m^{1/2}$ by assuming elliptical flaw of a semi-infinite solid, respectively. The $(Y_2O_3)ZrO_2/Al_2O_3$ eutectic fiber showed a radial (Palmqvist) crack type and exhibited an orthotropic crack growth behavior under 100 g load.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2009.11a
• /
• pp.11.1-11.1
• /
• 2009

Ternary Al2O3.ZrO2.Y2O3 samples with a eutecticcomposition were prepared by slow cooling. The microstructural evolution wasobserved with X-ray diffraction (XRD), scanning electron microscopy (SEM). TheSEM observation of the ternary samples agreed with the XRD with a completion ofcrystallisation by slow cooling. The target materials commonly have 'cantaloupe skin' microstructures as shown inthe previous studies by Han et al. The nanocomposite may have experienceddifferent cooling rates with two different microstructures, near the surfacehaving experienced optimal conditions for the eutectic reaction during theircooling and thus formed the eutectic microstructure, near the centre havingexperienced a slower cooling rate. The crystallised eutectic ternary Al2O3.ZrO2.Y2O3 system had three different phaseswith a 3Y2O3. 5Al2O3 (yttrium.aluminiumgarnet phase), an alumina phase formed by the eutectic reaction, and a solidsolution of ZrO2 and Y2O3.

• Journal of the Mineralogical Society of Korea
• /
• v.30 no.3
• /
• pp.127-136
• /
• 2017

High pressure has been applied to check the pressure effect on the powdered $TiO_2$-complex, which was synthesized for ultra-violet rays cutoff and antimicrobial applications. $TiO_2$-complex consists of anatase, rutile and silver chloride. Grain size was determined to be ~34 nm. Both anatase and rutile begin structural phase transitions to $ZrO_2$ (baddeleyite)-type crystal structures at 14~16 GPa, then sustain their phases up to 22.7 GPa. Under decompression to 0.0001 GPa (ambient pressure), rutile transforms to another phase with ${\alpha}-PbO_2$ structure, while anatase retains its high pressure structure upon complete decompression. Silver chloride peaks disappear at the low pressures.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.18 no.3
• /
• pp.109-114
• /
• 2008

Novel green long persistent phosphors of $CaZrO_3$ : $HO_{3+}$ have been synthesized at high temperature with weak reduction atmosphere by traditional solid state reaction method. The role of $H_3BO_3$ as flux and the suitable concentration of Ho as activator on the $CaZrO_3$ : $HO_{3+}$ long persistent phosphors has been investigated. Crystals of $HO_{3+}$ doped $CaZrO_3$ long persistent phosphores were characterized by fluorescence spectrophotometer and photoluminescence (PL). The main emission spectra of 546 nm peak was revealed through synthesizing at high temperature in $N_2$ gas atmosphere. The after glow emission spectra of $CaZrO_3$ : $HO_{3+}$ long persistent phosphores arise at 546 nm peak of narrow range. because that revealed pure green color. Green long persistent phosphors have been observed in the system for over 5 h after UV irradiation (254 nm). The main emission peak was ascribed to $HO_{3+}$ ions transition from $^5F_4$, $^5S_2{\to}^5I_3$, and the after glow may be ascribed to the trap centers in the $CaZrO_3$ host lattice.

• Journal of the Korean Magnetics Society
• /
• v.16 no.4
• /
• pp.201-205
• /
• 2006

The electromagnetic properties and microstructure of the basic composition of $(Ni_{0.2}Cu_{0.2}ZnO_{0.2})_{1.02}(Fe_{2}O_{3})_{0.98}$ were invested, changing the amount of the additives $Bi_2O_3$ and $ZrO_2$ and sintering temperature. The spinel structure of specimen was confirmed by the analysis of XRD patterns. Grain size and its density are increased by increasing the additive and the sintering temperature.However, the permeability increased with decreasing additive. It was also found that $Bi_2O_3$ had more effect on the increase of grain size and permeability rather than $ZrO_2$.