• Journal of the Korean Ceramic Society
• /
• v.40 no.1
• /
• pp.5-10
• /
• 2003

Porous barium-strontium titanate ceramics were fabricated by adding corn- or potato-starch (are referred to as starch). The effect of sintering temperature on the microstructure and electrical properties of the porous ceramics was investigated. The room-temperature electrical resistivity of the barium-strontium titanate ceramics decreased with sintering temperature. The porosity and pore size were decreased and the grain size was increased with increasing the sintering temperature. The porosity and grain size of the barium-strontium titanate ceramics with corn-starch sintered at 1300 and 1450$^{\circ}C$ were 28.5, 22.6% and 3.2, 6.2 $\mu\textrm{m}$, respectively. The average pore sizes of the barium-strontium titanate ceramics with corn-starch sintered at 1300, 1400 and 1450$^{\circ}C$ were 0.5, 0.3 and 0.2 $\mu\textrm{m}$, respectively. The decrease in the room-temperature resistivity with increasing sintering temperature is attributed mainly due to the increase of grain size and the decrease of the electrical barrier height of grain boundaries as well as the partial decrease of porosity.

• Journal of the Korean Ceramic Society
• /
• v.20 no.2
• /
• pp.107-114
• /
• 1983

Formation of Strontium titanate from the products of coprecipitation takes place at 110$0^{\circ}C$ which is 200-30$0^{\circ}C$ lower than that from mechanical mixtures of $SrCO_3$ and $TiO_2$. This is apparently due to the nature of the compounds formed by the reaction of mixtures of aqueous solutions of $SrCl_2$ and $TiCl_4$ with an ammoniacal solution of ammoni-um carbonate and ammonium hydroxide. A procedure is described for preparing strontium titanyl oxalate tetrahydrate in the several mole ratio of $TiCl_4$ to $SrCl_2$. STrontium titanyl oxalates decompose to titanate at elevated temperature. The coprecipitates and the fired specimen were subjected to examined thermal and X-ray analyses and microstruc-ture by SEM.

• Journal of the Korean Chemical Society
• /
• v.7 no.4
• /
• pp.254-256
• /
• 1963

A spectrochemical analysis was made to compare the major impurities in $BaTiO_3$ single crystals grown from $KF-BaTiO_3$ system and $TiO_2-BaTiO_3$ system respectively. The present technique was also extended, without any modifications, to the analysis of $SrTiO_3$ crystal.

• 한국신재생에너지학회:학술대회논문집
• /
• 2010.11a
• /
• pp.80.1-80.1
• /
• 2010

A strontium titanate ($SrTiO_3$)-based material with a perovskite structure is considered to be one of the promising alternatives to $LaCrO_3$-based materials since $SrTiO_3$ perovskite shows a high chemical stability under both oxidizing and reducing atmospheres at high temperatures. $SrTiO_3$ materials exhibit an n-type semiconducting behavior when it is donor-doped and/or exposed to a reducing atmosphere. In this work, $Sr_{1-x}La_xTi_{1-y}M_yO_3$ materials doped with $La^{3+}$ in A-sites and aliovalent transition metal ions ($M^{n+}$) in B-sites were synthesized by the modified Pechini method. The X-ray diffraction analysis indicated that the materials synthesized by the Pechini process exhibited a single curbic perovskite-type structure without any impurity phases, and are tolerant, to some extent, to cation doping. The sintering behaviors of $Sr_{1-x}La_xTi_{1-y}M_yO_3$ in $H_2/N_2$ and air were characterized by dilatometry and microstructural observations. The electrical conduction mechanism and the dopant effect are discussed based on the defect structures and the electrical conductivities measured at various oxygen partial pressures and temperatures.

• Proceedings of the Korea Crystallographic Association Conference
• /
• 2002.11a
• /
• pp.19-19
• /
• 2002

Perovskite-type titanate dielectrics have attracted much attention in memory devices such as DRAMs or FeRAMs due to their high dielectric constants. However, low volatility of the Ba, Sr, Pb or Zr precursors with only thd ligands has limitations in obtaining high quality thin films by liquid source metal organic chemical vapor deposition (LS-MOCVD) processes. To improve the volatility of these precursors, many attempts have been made such as adding polyether ligands to satisfy the coordinative saturation. We report the synthesis of new precursors Ba(thd)₂(tmeea) and Sr(thd)₂(tmeea), where tmeea = tris[2-(2-methoxyethoxy)ethyl]amino, and LS-MOCVD of barium strontium titanate (BSTO) thin films using these precursors. Due to increased basicity of amines compared with ethers, it is expected that the nitrogen-donor ligand will make a strong bond to a metal than an analogous oxygen-donor ligand, consequently improving the volatility and thermal behavior of these precursors. Thin films of BSTO were grown on Pt(111)/SiO₂/Si(100) substrates by LS-MOCVD using a cocktail source consisting of the conventional Ti precursor Ti(thd)₂(O/sup i/Pr), and these new Ba and Sr precursors. As-grown films were characterized by XPS, SEM, XRD, XRF, and C-V and I-V measurements. BSTO films grown at 420℃ were stoichiometric barium strontium titanate with very smooth surface morphology and their dielectric constants were found to be as targe as 450. Dependence of the composition, microstructure and the electrical properties of the BSTO films on the growth temperature, annealing temperature, working pressure, and the composition of the cocktail source will be discussed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2007.11a
• /
• pp.219-220
• /
• 2007

실란 커플링제 종류에 따른 $SrTiO_3$/유기물 복합재료의 유전특성에 미치는 영향을 조사하여 비교하였다. 실란 커플링제는 amino계, epoxy계, methacryloxy계, acryloxy계, vinyl계를 사용하였으며, tape casting 방법으로 제작한 복합체 필름을 vacuum lamination 공정을 통하여 기판을 만들어 유전특성을 측정하였다. 실란 괴플링제의 종류에 따라 유전특성은 상이한 결과를 나타냈으며, acryloxy계를 제외한 다른 커플링제를 처리한 복합재료는 유전상수와 유전손실이 감소하는 경향을 확인할 수 있었다. Acryloxy계 커플링제를 처리한 복합재료는 커플링제가 처리되지 않은 복합재료와 비교하여 유전상수가 6%정도 증가하였며, 유전손실은 25%정도 감소하였다.

• Proceedings of the Korean Radioactive Waste Society Conference
• /
• 2018.11a
• /
• pp.428-429
• /
• 2018

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.5 no.3
• /
• pp.215-222
• /
• 1995

Nb doped strontium titanate single crystals were grown by the floating zone method. The doping amount of $Nb_2O_5$ was 0.2 wt %. Those crystals were grown in air and N z atmosphere and the growth rate was 5 mmlhr and rotation speed of upper and lower shaft was 30 rpm. The shapes of melt - feed rod interface depending on sintering temperatures were observed. In air atmosphere, the flow rate of air was 1.5 ${\ell}/min$ and in $N_2$ atmosphere, that of $N_2$ gas was 0.5 ${\ell}/min$. As grown crystals were analyseQ by XRD, Laue back - reflection and chemical etching. After annealing in $N_2$ atmosphere, resistivities of crystals were measured and the activation energies of each samples were calculated.

• Environmental Engineering Research
• /
• v.23 no.3
• /
• pp.330-338
• /
• 2018

This study investigated the possibility of using potassium titanate oxide ($K_2Ti_4O_9$) and acrylic acid-grafted polypropylene fabric (PP-g-AA) as adsorbents capable of removing strontium from aqueous solutions. $K_2Ti_4O_9$ showed the highest rate of strontium removal in the weak alkaline range, while the PP-g-AA increased strontium removal in the neutral range. Moreover, the adsorption capacity of the $K_2Ti_4O_9$ was not affected by the coexistence of K and Na ions, while the adsorption capacity decreased when Ca and Mg ions were present at the same concentration as that of strontium. When coexisted at the same concentration as strontium, Na, K, Ca, and Mg ions strongly reduced the adsorption capacity of the PP-g-AA. The results also indicated that the adsorption of strontium on $K_2Ti_4O_9$ was consistent with both the Langmuir and Freundlich adsorption isotherms. In contrast, the adsorption of strontium on the PP-g-AA was more consistent with the Langmuir isotherm model. Moreover, the adsorption equilibrium time of $K_2Ti_4O_9$ was generally 12 h, while that of the PP-g-AA was 5 h, indicating that the adsorption rates were consistent with the pseudo-second order kinetics model. $K_2Ti_4O_9$ and the PP-g-AA could be regenerated by simple washing with 0.5 N HCl.

• Bulletin of the Korean Chemical Society
• /
• v.16 no.12
• /
• pp.1180-1184
• /
• 1995

The precursors of Ba1-xSrxTiO3(x=0.0-0.3) were prepared by the rapid addition of aqueous solution of titanyl oxalate to the mixed aqueous solution of barium and strontium at room temperature. The optimum pH was theoretically calculated from the equilibrium constants and solubility products. The chemical formula of the precursors obtained corresponded to Ba1-xSrxTiO(C2O4)2·4H2O(x=0.0-0.3) as determined by thermal gravimetric analysis. The precursors were converted to stoichiometric Ba1-xSrxTiO3(x=0.0-0.3) with a particle size of 0.01-0.04 μm. As increasing the amount of strontium substituted to barium sites, the structure of crystal changed from the tetragonal phase to the cubic and the unit cell volume was decreased.