• Korean Journal of Materials Research
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• v.34 no.1
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• pp.34-43
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• 2024

New piezoelectric and triboelectric materials for energy harvesting are being widely researched to reduce their processing cost and complexity and to improve their energy conversion efficiency. In this study, BaTiO₃ films of various thickness were deposited on Ni foams by R.F. magnetron sputtering to study the piezoelectric and triboelectric properties of the porous spongy structure materials. Then piezoelectric nanogenerators (PENGs) were prepared with spongy structured BaTiO₃ and PDMS composite. The output performance exhibited a positive dependence on the thickness of the BaTiO₃ film, pushing load, and poling. The PENG output voltage and current were 4.4 V and 0.453 ㎂ at an applied stress of 120 N when poled with a 300 kV/cm electric field. The electrical properties of the fabricated PENG were stable even after 5,000 cycles of durability testing. The triboelectric nanogenerators (TENGs) were fabricated using spongy structured BaTiO₃ and various polymer films as dielectrics and operated in a vertical contact separation mode. The maximum peak to peak voltage and current of the composite film-based triboelectric nanogenerator were 63.2 V and 6 ㎂, respectively. This study offers new insights into the design and fabrication of high output nanogenerators using spongy structured materials.

• Journal of the Korean Ceramic Society
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• v.40 no.1
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• pp.37-45
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• 2003

The dielectric and sintering characteristics of composites made by substituting Ca ion to Ba-site and Zr ion to Ti site in $(Ba{1-x}Ca_x)(Ti{0.96-yZr_ySn_{0.04})O_3$ $(0.15{\leq}x{\leq}0.20,\;0.09{\leq}y{\leq}0.14)$ were investigated. As the content of Ca was more than 15 mol%, composite was formed by precipitating the second phase whose main element was $CaTiO_3$ and the fraction of the second phase was increased. The curie temperature of composites was depended on Ca concentration, $-1.7^{\circ}C$ per mol% and the maximum dielectric constant of composite was decreased by the rate of 200/mol%. The substitution of Zr ion decreased the curie temperature by the rate of $10^{\circ}C$ per mol% and the maximum dielectric constant was decreased by 217/mol% due to the increase of diffuse phase transition. The density and insulation breakdown characteristics were improved by suppressing the abnormal grain growth due to the increase of second phase. We developed the composition of Y5U (EIA standard) condenser which had high breakdown voltage and dielectric constant by controlling diffuse phase transition by the addition of Zr ion into composite.

• Journal of the Korean Ceramic Society
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• v.21 no.2
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• pp.121-126
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• 1984

The dielectric properties of $BaTiO_3$ containing 0~0.3mol% and ZnO respectively as additives were investigated as a function of temperature from $25^{\circ}C$ to 14$0^{\circ}C$ and frequency from 24 KHz to 15MHz. The density of sintered $BaTiO_3$ was increased with addition of increasing to 0.15mol% amounts of $Sb_2O_3$ and the dielectric constant was also increased. This is due to space charge polarization with Ba vacancies. Above 0.15mol% $Sb_2O_3$ the density was decreased and the dielectric constant was also decreased due to occuring the discharge through voids. The density of sintered $BaTiO_3$ was decreased with addition of increasing to 0.15mol% amounts of ZnO and the dielectric constant was decreased due to occuring the discharge through voids. Above 0.15mol% ZnO the density was increased and the dielectric constant was also increased.

• Applied Chemistry for Engineering
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• v.3 no.3
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• pp.412-421
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• 1992

The superconducting thin films have shown a growing possibility for practical application in microelectronic fields in recent years. In this study, the high Tc superconducting Y-Ba-Cu-O thin films were prepared on various substrates by chemical vapor deposition method using organic metal chelates of $Y(thd)_3$, $Ba(thd)_2$, and $Cu(thd)_2$ as source materials. The deposition reactions were carried out on single crystalline MgO(100), YSZ(100), $SrTiO_3(100)$, and polycrystalline $SrTiO_3$ substrates. Deposition thickness of thin films was linearly increased with the increase of deposition time. It turned out that the Y-Ba-Cu-O thin films on MgO(100), YSZ(100), and $SrTiO_3(100)$ single crystal substrates showed superconductivities above liquid nitrogen temperature($T_{c,onset}=87{\sim}89K$, $T_{c,zero}=85{\sim}86K$), but the one on polycrystalline $SrTiO_3$ substrate did not.

• Proceedings of the Korean Ceranic Society Conference
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• 2002.10a
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• pp.95.1-95
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• 2002

• Fire Science and Engineering
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• v.16 no.4
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• pp.15-19
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• 2002

This dissertation is about the development of $BaTiO_3$-type PTC(Positive Temperature Coefficient) thermistor by composition method. A multilayer-type PTC samples were fabricated under optimal conditions after setting the experimental composition equation as ($Ba_{0.95-x}$S $r_{0.05}$$Ca_{x}$ )$TiO_3$-$0.01TiO_2$-$0.01SiO_2$-$\alpha$$MnCO_3$-$\beta$N $b_2$ $O_{5}$.) and their testing results were analyzed. The optimal sin-tering and cooling temperatures were 13$50^{\circ}C$ for two hours and $100^{\circ}C$/h for an hour, respectively; By composing Ca and Mn, dopants to lower the resistivity at room temperature, and Nb, a dopant to raise peak resistivity(Ca:5 mol%, Mn:0.08 mol%, Nb:0.18 mol%), appropriately, a PTC thermistor, having the characteristics of relatively low resistivity at room temperature and high peak resistivity and a good temperature coefficient, has been developed. And we find that it is possible of application for fire detection sensor.r.r.

• Journal of the Korean Ceramic Society
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• v.28 no.3
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• pp.179-188
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• 1991

The semiconducting BaTiO3 ceramics used in this study were sintered in the reducing atomosphere(hydrogen gas) and neutral atmosphere(nitrogen gas), then were heat-treated in air to vary defect concentrations. In this experiment, the correlations between the composition analysis and electrical characteristics of these samples were investigated. When the BaTiO3 ceramics were sintered in N2 atmosphere, it was observed that the Ba contents near the interface were lower than that of the grain center, and these samples showed superior PTCR effects. From analysis of the resistivities of grains and grain boundaries by CIRM(Complex Impedance Resonance Method), it was confirmed that the PTCR effects were caused by the resistivity of grain boundaries. And from measurement of the capacitance at each temperature, the samples sintered in N2 atmosphere show the increase of room temperature resistance and the decrease of capacitance as a result of the increase of the charge depletion layers. This phenomenon agrees well with the cation deficiencies in the analytical results.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.11
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• pp.933-938
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• 2002

(Ba,Sr)TiO$_{4}$ (BST) thin films on Pt/Ti/SiO$_{2}$/Si substrates were deposited by a sol-gel method and the etch characteristics of BST thin films have been investigated as a function of gas mixing ratio. The maximum etch rate of the BST films was 440 $AA$/min under such conditions as: CF$_{4}$(CF$_{4}$＋Ar) of 0.2, RF-power of 700 W, DC-bias voltage of -200 V, pressure of 15 mTorr and substrate temperature of 30 $^{circ}C$. The selectivities of BST to Pt, SiO$_{2}$ and PR were 0.38, 0.25 and 0.09, respectively. In the XPS (X-ray photoelectron spectroscopy) analysis, Barium (Ba) and Strontium (Sr) component in BST thin films formed low volatile compounds such as BaFx, SrFx, which are forms by the chemical reaction with F atoms and is removed by Ar ion bombardment. Titanium (Ti) is removed by chemical reaction such as TiF with ease. The result of secondary ion mass spectrometry (SIMS) analysis confirmed the existence of the BaFx, SrFK, TiFx.

• Analytical Science and Technology
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• v.17 no.2
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• pp.173-179
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• 2004

The $BaTiO_3$ powders and thin films were prepared by an alkoxide modified sol-gel process (polymerization-complex route) using ethylene glycol. The stable starting (Ba-Ti)-mixed metal organic sol was made by addition of acetylacetone. The $BaTiO_3$ powders, which had a particle size of 40~77 nm, were crystallized from an amorphous to a tetragonal phase on annealing at 700 and $1100^{\circ}C$ for 1 h. From FT-IR, solid-state $^{13}C$ CP/MAS NMR spectroscopy and X-ray diffractometry, the trace of the Ba-Ti-oxycarbonate phase first appeared at $400^{\circ}C$. Hydrolyzed sol was spin coated on a quartz wafer at 3500 rpm for 60 s and pyrolyzed at $1100^{\circ}C$ for 1 h. After heat treatment, the coated layer became dense and smooth.

• The Journal of Natural Sciences
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• v.1
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• pp.33-45
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• 1987

$BaCO_3$ 와 다양한 입자크기의 $TiO_2$ 의 고체상태 반응을 산소 ( 혹은 공기 ) 와 이산화탄소 중에서 열중량 분석법 (TG) 과 시차 열분석법 (DTA) 를 이용하여 반응속도론 및 반응기구를 조사하였다. 중간생성물과 최종생성물의 확인은 X-ray 회절 분석법 (XRD) 을 이용하였다. $TiO_2$ 의 반응성은 입자의 크기가 $0.15\mum$이하일 때 현저히 증가하였다. 반응초기에 $BaTiO_3$ 는 반응물의 접촉표면에서 생기기 시작하며 반응의 진행과정은 Jander 에 따라 확산조절과정이 된다. 반응과정에서 BaO-$TiO_2$ 의 상평형도에 기술된 화합물들이 중간물질로써 나타난다. 공기중에서는 상당한 양의 $Ba_2$$TiO_4$ 가 생성되지만 $CO_2$ 의 분위기에서는 약 $1100^{\circ}C$까지 억제된다. 이 온도는 열역학적 계산치인 $1060\pm$ $50^{\circ}C$와 잘 일치하고 있다. 확산과정의 활성화 에너지 값은 공기중에서는 56.4Kcal/mol 이었으며 이산화탄소의 경우에서는 79.6Kacl/mol 이었다.