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Ryu, Jungho,Han, Guifang,Lee, Jong-Pil,Lim, Dong-Soo,Park, Yun-Soo,Jeong, Dae-Yong American Scientific Publishers 2013 Journal of Nanoscience and Nanotechnology Vol.13 No.5
<P>Spinel structured highly dense NiMn2O4-based (NMO) negative temperature coefficient (NTC) thermistor thick films were fabricated by aerosol-deposition at room temperature. To enhance the thermistor B constant, which represents the temperature sensitivity of the NMO thermistor material, Co and Co-Fe doping was applied. In the case of single element doping of Co, 5 mol% doped NMO showed a high B constant of over 5000 K, while undoped NMO showed -4000 K. By doping Fe to the 5 mol% Co doped NMO, the B constant was more enhanced at over 5600 K. The aging effect on the NTC characteristics of Co doped and Fe-Co co-doped NMO thick film showed very stable resistivity-time characteristics because of the highly dense microstructure.</P>
Ryu, Jungho,Han, Guifang,Song, Tae Kwon,Welsh, Aaron,Trolier-McKinstry, Susan,Choi, Hongsoo,Lee, Jong-Pil,Kim, Jong-Woo,Yoon, Woon-Ha,Choi, Jong-Jin,Park, Dong-Soo,Ahn, Cheol-Woo,Priya, Shashank,Choi, American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.15
<P>Thick polycrystalline pure PbTiO<SUB>3</SUB> films with nano size grains were synthesized for the first time by aerosol deposition. Annealed 7 μm thick films exhibit well-saturated ferroelectric hysteresis loops with a remanent polarization and coercive field of 35 μC/cm<SUP>2</SUP> and 94 kV/cm, respectively. A large-signal effective <I>d</I><SUB>33,eff</SUB> value of >60 pm/V is achieved at room temperature. The measured ferroelectric transition temperature (<I>T</I><SUB>c</SUB>) of the films ∼550 °C is >50 °C higher than the reported values (∼490 °C) for PbTiO<SUB>3</SUB> ceramics. First-principles calculations combined with electron energy loss spectroscopy (EELS) and structural analysis indicate that the film is composed of nano size grains with slightly decreased tetragonality. There is no severe off-stoichiometry, but a high compressive in-plane residual stress was observed in the film along with a high transition temperature and piezoelectric response. The ferroelectric characteristics were sustained until 200 °C, providing significant advancement toward realizing high temperature piezoelectric materials.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-15/am5000307/production/images/medium/am-2014-000307_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am5000307'>ACS Electronic Supporting Info</A></P>
Amperometric Determination of Nitrite at Poly(Methylene Blue)-Modified Glassy Carbon Electrode
Xu, Guang-Ri,Xu, Guifang,Xu, Ming-Lu,Zhang, Zhengqing,Tian, Yuan,Choi, Han-Nim,Lee, Won-Yong Korean Chemical Society 2012 Bulletin of the Korean Chemical Society Vol.33 No.2
Electrochemical characteristics of nitrite ion were investigated at a poly(methylene blue)-modified glassy carbon electrode by cyclic voltammetry and differential pulse voltammetry. The poly(methylene blue)-modified glassy carbon electrode exhibited enhanced anodic signals for nitrite. The effects of key parameters on the detection of nitrite were evaluated at the modified electrode, such as pH, accumulation time, and scan rate. Under optimum condition, the chemically modified electrode can detect nitrite in the concentration range $2.0{\times}10^{-6}$ to $5.0{\times}10^{-4}$ M with the detection limit of $2.0{\times}10^{-6}$ M and a correlation coefficient of 0.999. The detection of nitrite using the chemically modified electrode was not affected by common ions such as $Na^+$, $K^+$, $Ca^{2+}$, $Cl^-$, $HPO_4^{2-}$ and $H_2PO_4^- $. The modified electrode showed good stability and reproducibility. The practical application of the present method was successfully applied to the determination of nitrite ion in cabbage samples.
Photosensitive Al2O3 slurry with high solid content and low viscosity
Zhang Xu,Zhang Jingde,Tian Yuhang,Xiao Shikang,Li Jianzhang,Han Guifang 한국세라믹학회 2023 한국세라믹학회지 Vol.60 No.3
Slurries with high solid content and low viscosity are highly necessary to lower the sintering shrinkage and avoid possible defects for ceramic components fabricated by vat photopolymerization technique. However, the viscosity of slurry dramati- cally arises with the increase of solid content, which severely affects the printing process and the quality of preformance. To solve this issue, a novel combined strategy of powder surface modification and selection of dispersant was proposed to significantly increase the solid load without too much increase in viscosity. The surface of Al 2O3 particles was modified by Silane A174 to improve its wettability with resins, and then the use of KOS 110 formed steric hindrance between particles achieving good dispersion. The synergistic effect of the modifier and dispersant was realized. Al 2O3 slurry with a high solid loading up to 65 vol% and low viscosity of 20.0 Pa·s at 30 s −1 was prepared for stereolithography-based DLP 3D printing, which had among the highest performance in photosensitive Al 2O3 slurries.
Kumar Ajeet,Lee Geon,Thakre Atul,Patil Deepak Rajaram,Han Guifang,Ryu Jungho 한국세라믹학회 2023 한국세라믹학회지 Vol.60 No.6
This study reports the fabrication of manganese (Mn) doped antiferroelectric (AFE) thick fi lms (thickness of ~ 2 μm) of (Pb0.93 La0.07 )(Zr0.82 Ti0.18 )O3 (PLZT 7/82/18) at room temperature using aerosol deposition (AD) technique without any additional thermal treatment. The Mn-doped PLZT 7/82/18 AD thick fi lms demonstrate excellent energy storage and electrical properties despite being fabricated at room temperature. The dielectric properties of the PLZT AD thick fi lms were investigated across a frequency range of 100 Hz–1 MHz and a temperature range of 25–250 o C. The Mn-doped PLZT AD thick fi lms exhibit a dielectric constant of ~ 108, low dielectric loss of 0.0211, and high-temperature stability of ~ 5.5% (from 1 kHz to 1 MHz). The bipolar P-E and I-E hysteresis loops of the PLZT AD thick fi lms do not show an AFE behavior, however, resemble the paraelectric/dielectric type of loops. The Mn-doped PLZT AD thick fi lms exhibit high dielectric breakdown strength (DBS) of ~ 5420 kV/cm, energy-storage density (ESD) of ~ 38.7 W/cm 3 , with high energy effi ciency of ~ 71%. Additionally, the Mn-doped PLZT AD thick fi lms demonstrate a low leakage current and excellent fatigue properties, as indicated by the obtained polarization, DBS, ESD, and energy effi ciency after 10 8 cycles.