• 한국전기전자재료학회논문지
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• 제25권8호
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• pp.664-669
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• 2012

Nano-structured one-dimensional $Na_2Ti_6O_{13}$ particles were synthesized by a molten salt process. Effects of processing parameters on the microstructure and band gap energy of the $Na_2Ti_6O_{13}$ powder were studied in this paper. For the synthesis of the $Na_2Ti_6O_{13}$ particles, two different raw materials of tubular shaped Na-titanate (Na-TiNT) and spherical shaped $TiO_2$ were utilized. Synthesizing with the raw material of Na-TiNT, around 70nm thick 1D-$Na_2Ti_6O_{13}$ with the bandgap energy of 3.5 eV was obtained at $810^{\circ}C$. Below $810^{\circ}C$ or without the presence of NaCl, 1D-$Na_2Ti_6O_{13}$ was in a relatively short in length and agglomerated state. With the processing temperature increased, the thickness of the 1D-$Na_2Ti_6O_{13}$ was also observed to be increased. On the other hand, when $TiO_2$ was employed as a raw material, the mixed amount of $Na_2CO_3$ played an important role in transforming the morphology and phase of the raw material, affecting the bandgap energy of the synthesized product. Specific surface area of the synthesized 1D-$Na_2Ti_6O_{13}$ was significantly affected by the raw and mixed materials as well as processing temperature. When Na-TiNT was processed at $810^{\circ}C$ with NaCl, the specific surface area of the 1D-$Na_2Ti_6O_{13}$ showed the best value of 30.63 $m^2/g$.

• 한국분말재료학회지
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• 제29권6호
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• pp.492-498
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• 2022

N-doped Na₂Ti₆O₁₃@TiO₂ (denoted as N-NTO@TiO₂) composites are successfully synthesized using a simple two-step process: 1) ball-milling of TiO₂ with Na₂CO₃ followed by heat treatment at 900℃; 2) mixing of the prepared Na₂Ti₆O₁₃ with titanium isopropoxide and calcining with urea at 500℃. The prepared composites are characterized using XRD, SEM, TEM, FTIR, and BET. The N-NTO@TiO₂ composites exhibit well-defined crystalline and anatase TiO₂ with exposed {101} facets on the external surface. Moreover, dopant N atoms are uniformly distributed over a relatively large area in the lattice of the composites. Under visible light irradiation, ~51% of the aqueous methylene blue is photodegraded by N-NTO@TiO₂ composites, which is higher than the values shown by other samples because of the coupling effects of the hybridization of NTO and TiO₂, N-doping, and presence of anatase TiO₂ with exposed {101} facets.

• Corrosion Science and Technology
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• 제11권2호
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• pp.65-69
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• 2012

One dimensional(1D) $Na_2Ti_6O_{13}$ nanorods with 70 nm in diameter was synthesized by a molten salt method. Using the synthesized nanorods, about 750 nm thick $Na_2Ti_6O_{13}$ film was coated on Fluorine-doped tin oxide(FTO) glasss substrate by the Layer-by-layer self-assembly(LBL-SA) method in which a repetitive self-assembling of ions containing an opposite electric charge in an aqueous solution was utilized. Using the Kubelka-Munk function, the band gap energy of the 1D-$Na_2Ti_6O_{13}$ nanorods was nalyzed to be 3.5 eV. On the other hand, the band gap energy of the $Na_2Ti_6O_{13}$ film coated on FTO was found to be a reduced value of 2.9 eV, resulting from the nano-scale and high porosity of the film processed by LBL-SA method, which was favorable for the photo absorption capability. A significant improvement of photocurrent and onset voltage was observed with the $Na_2Ti_6O_{13}$ film incorporated into the conventional $Fe_2O_3$ photoelectrode: the photocurrent increased from 0.25 to 0.82 mA/$cm^2$, the onset voltage decreased from 0.95 to 0.78 V.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2010년도 하계학술대회 논문집
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• pp.15-15
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• 2010

$Na_2Ti_6O_{13}$ (NT)가 도핑된 $BaTiO_3-(Bi_{0.5}Na_{0.5})TiO_3$ BBNT) PTCR 세라믹스를 변형된 세라믹공정을 이용하여 제조하였다. 제조된 BBNT 세라믹의 미세구조와 PTCR 특성에 미치는 NT의 효과를 조사하였다. $1300^{\circ}C$에서 합성된 BBNT 세라믹은 NT의 도핑량이 증가함에 따라 비정상적으로 성장된 입자의 수가 증가하였다. 뿐만 아니라, NT의 도핑량 증가는 상온비저항을 약간 증가시켰지만 큐리온도 (Tc) 부근의 최대비저항/최소비저항으로 정의되는 PTC 점프 특성을 크게 향상시켰다. 특히, 0.01mol%의 NT 도핑 시 상온비저항은 $425\;\Omega{\cdot}cm$, PTC 점프는 ($2.02{\times}^10^5$) 저항온도계수는 69.8% 및 Tc는 $155^{\circ}C$의 우수한 결과를 나타내었다.

• 공업화학
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• 제9권4호
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• pp.585-590
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• 1998

섬유상의 $Na_xTi_nO_{2n+1}$는 층상구조의 $H_2Ti_4O_9{\cdot}nH_2O$에대한 $H^+/Na^+$의 이온교환에 의해서 합성되었다. 이온교환 반응은 0.5~2.0 M NaOH 용액에서 이루어졌으며, 2.0 M NaOH의 용액에서 이온 교환할 때 73%가 치환되었다. 이 때 길이가 $10{\sim}20{\mu}m$이고 직경이 약 $0.7{\mu}m$인 비교적 균일한 형태의 섬유상을 얻을 수 있었다. 그리고 층상구조의 티탄산나트륨에 대한 상전이는 열분석을 통해 확인하였으며, 이 결과 $Na_xTi_nO_{2n+1}$ 섬유는 $200{\sim}600^{\circ}C$의 온도에서 $Na_2Ti_6O_{13}$과 $TiO_2$로 분해되었다.

• 한국재료학회지
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• 제20권11호
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• pp.575-580
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• 2010

The microstructure and positive temperature coefficient of resistivity (PTCR) characteristics of 0.1 mol%$Na_2Ti_6O_{13}$ doped $0.94BaTiO_3-0.06(Bi_{0.5}Na_{0.5})TiO_3$ (BBNT-NT001) ceramics sintered at various temperatures from $1200^{\circ}C$ to $1350^{\circ}C$ were investigated in order to develop eco-friendly PTCR thermistors with a high Curie temperature ($T_C$). Resulting thermistors showed a perovskite structure with a tetragonal symmetry. When sintered at $1200^{\circ}C$, the specimen had a uniform microstructure with small grains. However, abnormally grown grains started to appear at $1250^{\circ}C$ and a homogeneous microstructure with large grains was exhibited when the sintering temperature reached $1325^{\circ}C$. When the temperature exceeded $1325^{\circ}C$, the grain growth was inhibited due to the numerous nucleation sites generated at the extremely high temperature. It is considered that $Na_2Ti_6O_{13}$ is responsible for the grain growth of the $0.94BaTiO_3-0.06(Bi_{0.5}Na_{0.5})TiO_3$) ceramics by forming a liquid phase during the sintering at around $1300^{\circ}C$. The grain growth of the BBNT-NT001 ceramics was significantly correlated with a decrease of resistivity. All the specimens were observed to have PTCR characteristics except for the sample sintered at $1200^{\circ}C$. The BBNT-NT001 ceramics had significantly decreased $\tilde{n}_{rt}$ and increased resistivity jump with increasing sintering temperature at from $1200^{\circ}C$ to $1325^{\circ}C$. Especially, the BBNT-NT001 ceramics sintered at $1325^{\circ}C$ exhibited superior PTCR characteristics of low resistivity at room temperature ($122\;{\Omega}{\cdot}cm$), high resistivity jump ($1.28{\times}10^4$), high resistivity temperature factor (20.4%/$^{\circ}C$), and a high Tc of $157.9^{\circ}C$.

• 한국세라믹학회지
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• 제53권3호
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• pp.282-287
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• 2016

This study involves enhancing the performance of the $Na(Li,Ti)O_2$ system as an Na-ion battery anode with the addition of Mg, which partially replaces Li ions. We perform both computational and experimental approaches to achieve a higher reversible capacity and a faster transport of Na ions for the devised system. Computational results indicate that the $Na(Li,Mg,Ti)O_2$ system can provide a lower-barrier path for Na-ion diffusion than can a system without the addition of Mg. Experimentally, we synthesize various $Na_z(Li_y,Mg_x,Ti)O_2$ systems and evaluate their electrochemical characteristics. In agreement with the theoretical study, Mg addition to such systems improves general cell performance. For example, the prepared $Na_{0.646}(Li_{0.207}Mg_{0.013}Ti_{0.78})O_2$ system displays an increase in reversible capacity of 8.5% and in rate performance of 13.5%, compared to those characteristics of a system without the addition of Mg. Computational results indicate that these improvements can be attributed to the slight widening of the Na-$O_6$ layer in the presence of Mg in the $(Li,Ti)O_6$ layer.

• 한국세라믹학회지
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• 제40권6호
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• pp.577-582
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• 2003

공침전물을 원료로 사용한 수열합성법을 통해 저온에서 미립의 BaTiO$_3$ 분말을 합성하였다. 출발물질로는 BaCl$_2$와 TiCl$_4$ 의 수용액을 사용하였다 이들의 혼합용액을 제조한 다음 과산화물 형태의 침전을 얻기 위해 과산화수소수($H_2O$$_2$)를 첨가하였으며 이렇게 준비된 용액을 암모니아수에 적하하여 공침전물을 얻었다. 이 과산화공침전물을 수열합성의 원료로 사용하였으며 반응온도와 시간 및 pH를 달리하면서 합성하였다. pH 13 이상이 요구되어 강염기인 KOH나 NaOH를 사용하는 일반적인 수열합성법과 달리 암모나아수로도 얻을 수 있는 pH 12 이하에서 perovskite BaTiO$_3$가 합성되었으며, 11$0^{\circ}C$ 이상에서 균일하고 미세한 BaTiO$_3$ 분말을 합성할 수 있었다. 13$0^{\circ}C$ 이상에서 얻은 분말의 경우 합성시간과 관계없이 일정한 물성을 보여주었다. 이렇게 합성된 분말은 76 $m^2$/g의 높은 비표면적을 보였으며 20 nm 이하의 미세한 일차입자들이 약하게 결합된 응집체를 이루고 있었다. 수열합성분말을 이용하여 l150~120$0^{\circ}C$의 온도범위에서 소결한 시편의 소결특성 및 유전 물성을 평가하였다.

• Bulletin of the Korean Chemical Society
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• 제25권9호
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• pp.1341-1345
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• 2004

We developed a novel synthesis strategy of titania nanowire arrays by employing simple hydrothermal reaction and ion-exchange reaction techniques. Hydrothermal reactions of metallic titanium powder with $H_2O_2$ in a 10 M NaOH solution produced a new sodium titanate compound, $Na_2Ti_6O_{13}{\cdot}xH_2O$ (x~4.2), as arrays of nanowires of lengths up to 1 mm. Acid-treatment followed by calcination of this material produced arrays of highly crystalline anatase nanowires as evidenced by x-ray diffraction, Raman spectroscopy, and transmission electron microscopy studies. In both cases of sodium titanate and anatase, the nanowires have exceptionally large aspect ratios of 10,000 or higher, and they form arrays over a large area of $1.5 {\times} 3 cm^2$. Observations on the reaction products with varied conditions indicate that the array formation requires simultaneously controlled formation and crystal growth rates of the $Na_2Ti_6O_{13}{\cdot}xH_2O$ phase.

• E2M - 전기 전자와 첨단 소재
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• 제9권6호
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• pp.605-615
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• 1996

In this paper, the effect of alkaline oxide addition such as Li$_{2}$O and Na$_{2}$O on the microstructure and humidity sensitivity of V$_{2}$O$_{5}$(2 mol%)-doped TiO$_{2}$(98 mol%) was investigated as a function of amount (0, 1, 2, 5, 10 mol%) of Li$_{2}$O and Na$_{2}$O additives. The pores in the alkaline free sample were distributed mostly in the range between 0.16 and 1.0.mu.m in diameter and its porosity was 23.29%. Li$_{2}$O caused grain overgrowth and reduced the porosity with a narrow distribution of the pore size, leading to poor humidity sensitivity. Na$_{2}$O helped to enlarge the distribution of the pore size through the formation of small soluble phases. The pore sizes of the sample containing Na$_{2}$O 2mol% were distributed mostly in the range between 1.0 and 2.5.mu.m in diameter and its porosity and intrusion volume of mercury were 31.13 % and 0.1155 mL/g respectively, which consequently improved the humidity sensing characteristics such as the sensitivity and temperature-stability. Especially, the addition of 2mol% of Na$_{2}$O improved the humidity-sensing characteristics such as sensitivity and linearity in the whole range between 30 and 90 %RH (Percentage Relative Humidity)y)