Browsing by Author "Byung Cheol Sin"

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Combustion synthesis of nanostructured Ba0.8(Ca,Sr)0.2TiO3 ceramics and their dielectric properties
(Elsevier Ltd, 2015) Laxman Singh; Ill Won Kim; Byung Cheol Sin; Uma Shanker Rai; Seung Ho Hyun; Youngil Lee
Ba0.8(Ca,Sr)0.2TiO3 nanostructured ceramics were synthesized by a facile and glycine-assisted auto-combustion method using stable solid TiO2, which is better than other several chemical routes reported earlier involving expensive alkoxides, oxynitrates, or chlorides of titanium as the titanium sources. TGA/DSC analysis of precursor powder gives pre-information about formation of final product around 950 °C. XRD analysis confirms the formation of single-phase of the BCT and BST ceramics on sintering at 950 °C for 15 h. TEM image of the ceramics show nanocrystalline particles in the range 40–90 nm. Surface morphology indicates that the average grain size is in range of 55–140 nm and 45–120 nm for BCT and BST, respectively. Energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy confirmed the purity and stoichiometry. The value of the dielectric constant of BST (εr~368) ceramic is higher than BCT (εr~255) at 100 Hz at 308 K. The dielectric constant BST is higher than BCT at all measured temperatures and frequency ranges due to higher crystallinity and high grain-boundary resistance, as confirmed by impedance analysis. © 2015 Elsevier Ltd and Techna Group S.r.l.
Comparative Dielectric and Ferroelectric Characteristics of Bi0.5Na0.5TiO3, CaCu3Ti4O12, and 0.5Bi0.5Na0.5TiO3–0.5CaCu3Ti4O12 Electroceramics
(Springer New York LLC, 2016) Laxman Singh; Shiva Sundar Yadava; Byung Cheol Sin; Uma Shanker Rai; K.D. Mandal; Youngil Lee
Abstract: The dielectric and ferroelectric characteristics of Bi0.5Na0.5TiO3 (BNT), CaCu3Ti4O12 (CCTO), and 0.5Bi0.5Na0.5TiO3–0.5CaCu3Ti4O12 (BNT/CCTO) ceramics are compared. X-ray diffraction patterns confirmed the formation of single phase of all the ceramics after sintering at 950°C for 15 h. Scanning electron microscopy images of the sintered ceramics reveal average grain sizes in the range from 200 nm to 2.5 μm. Energy-dispersive x-ray mapping and x-ray photoelectron spectroscopy show the presence of the elements Bi, Na, Ca, Cu, Ti, and O with uniform distribution in the ceramics. BNT/CCTO exhibits high dielectric constant (εr ∼ 6.9 × 104) compared with BNT (εr ∼ 0.13 × 104) and CCTO (εr ∼ 1.68 × 104) ceramics at 1 kHz and 503 K. The high dielectric constant of BNT/CCTO compared with BNT and CCTO is associated with a major contribution from grain boundaries, as confirmed by impedance and modulus analyses. The P–E hysteresis loop of all the ceramics measured at room temperature and 50°C exhibited typical ferroelectric nature. The remanent polarization (Pr) of BNT (1.58 μC/cm2) and CCTO (0.654 μC/cm2) ceramics are higher than that of BNT/CCTO (0.267 μC/cm2) ceramic. Graphical Abstract: [Figure not available: see fulltext.] © 2016, The Minerals, Metals & Materials Society.
Comparative dielectric studies of nanostructured BaTiO3, CaCu3Ti4O12 and 0.5BaTiO3· 0.5CaCu3Ti4O12 nano-composites synthesized by modified sol-gel and solid state methods
(Elsevier Inc., 2014) Laxman Singh; Uma Shanker Rai; Kam Deo Mandal; Byung Cheol Sin; Hyung-Il Lee; Hoeil Chung; Youngil Lee
BaTiO3 (BTO), CaCu3Ti4O12 (CCTO) and 0.5BaTiO3·0.5CaCu3Ti4O 12 (BTO-CCTO), as a new nano-composite ceramic, were successfully designed and fabricated by a semi-wet gel route and a modified solid state method. The dielectric properties of the BTO-CCTO ceramic were compared to those of the BTO and CCTO ceramics at lower sintering temperatures and durations. The X-ray diffraction analysis revealed that the BTO and CCTO ceramics form a single crystalline phase and the average crystalline sizes calculated from X-ray diffraction data were in the range of 40-65 nm. The particle sizes of the BTO, CCTO, and BTO-CCTO ceramics obtained from transmission electron microscopy images were in the ranges of 40-65 nm, 80-110 nm, and 70-95 nm, respectively. The phase composition and microstructure were studied by X-ray diffraction and scanning electron microscopy. The energy dispersive X-ray results demonstrated the purity and stoichiometry of the BTO-CCTO nano-composite. The grain sizes of the BTO, CCTO and BTO-CCTO ceramics were found to be in the ranges of 500 nm-1 μm, 4-24 μm, and 250 nm-4 μm, respectively. The AC conductivity as a function of frequency confirmed the semiconducting nature of all of the ceramics and obeyed the Jonscher's power law. The impedance spectrum measurement result showed that the CCTO ceramic possessed an exceptional grain boundary resistance, which supports the internal barrier layer capacitance (IBLC) mechanism present in this ceramic and is responsible for the high εr values. © 2014 Elsevier Inc. All rights reserved.
Dielectric studies of a nano-crystalline CaCu2.90Zn0.10Ti4O12 electro-ceramic by one pot glycine assisted synthesis from inexpensive TiO2 for energy storage capacitors
(Royal Society of Chemistry, 2014) Laxman Singh; Ill Won Kim; Byung Cheol Sin; Kam Deo Mandal; Uma Shanker Rai; Amir Ullah; Hoeil Chung; Youngil Lee
A facile way for the synthesis of nano-crystalline CaCu2.90Zn0.10Ti4O12 (CCZTO) using a solution combustion technique based on the glycine-nitrate process with inexpensive solid TiO2 powder as the raw material is introduced in this manuscript, for the first time. The precursor powder was calcined between 200 °C and 850°C for 3 h in air. Phase formation, crystalline nature, morphology and chemical purity of the fabricated CCZTO were investigated with TG/DTA, FT-IR, FT-Raman, XRD, SAED patterns, SEM, TEM, EDX and XPS analyses, respectively. The XRD results indicated that all sintered samples had a major CaCu3Ti4O12 structure with some amount of CaTiO3 and CuO. The bright-field TEM micrographs revealed that the particle size was in the range of 15-50 nm, which was in good agreement with the average crystallite size obtained from XRD. SEM micrographs of the sintered CCZTO ceramics showed the average grain sizes were in the range of 800 nm-7 μm. EDX and XPS studies confirmed the stoichiometry and purity of the ceramics. The nature of the relaxation behavior of the ceramics was rationalized using impedance and modulus spectroscopy. The activation energies calculated from the grain-boundary relaxation time constant were found to be in the range of 0.79-0.52 eV, which confirmed the Maxwell-Wagner type of relaxation present in the ceramic. Our inexpensive novel solution chemistry based method for CCZTO-16h gives a high dielectric constant (799) and low dielectric loss (0.091) at 100 Hz at room temperature, which has potential significance for cost-effective technological applications in microelectronic devices. © the Partner Organisations 2014.
Dielectric, AC-impedance, modulus studies on 0.5BaTiO3·0. 5CaCu3Ti4O12 nano-composite ceramic synthesized by one-pot, glycine-assisted nitrate-gel route
(Elsevier Ltd, 2014) Laxman Singh; Uma Shanker Rai; Kamdeo Mandal; Byung Cheol Sin; Sang-Ick Lee; Youngil Lee
A nano-composite electro-ceramic with the chemical formula 0.5BaTiO 3·0.5CaCu3Ti4O12 (BTO-CCTO) has been synthesized by a glycine - assisted nitrate-gel route which is simpler and faster at relatively low temperature than the conventional solid-state synthesis method. X-ray diffraction (XRD) analysis showed the existence of BTO as a secondary phase alongside the major phase of CCTO. Transmission electron microscope (TEM) analysis of the composite shows that nano-particles (60±15 nm) were obtained. Further, scanning electron microscope (SEM) images show that the morphology consists of a few large grains of CCTO (∼1-5 μm) embedded in small grains of BTO (∼500 nm-1 μm) with a bimodal distribution. The impedance analysis shows two major contributions associated with the grains and the grain boundaries. Modulus analysis of this composite confirmed the presence of a Maxwell-Wagner type relaxation, which is temperature dependent. The activation energy value was found to be 0.80 eV, and this composite is electrically conductive due to the mobility of the ionized oxygen defects. © 2014 Elsevier Ltd and Techna Group S.r.l.
Structural, impedance, and modulus spectroscopic studies on y 2/3Cu 3Ti 3.95In 0.05O 12 polycrystalline material prepared by flame synthesis method
(Taylor and Francis Inc., 2016) Laxman Singh; Shiv Sunder Yadava; Won Seok Woo; Uma Shanker Rai; K.D. Mandal; Byung Cheol Sin; Youngil Lee
The polycrystalline material Y2/3Cu3Ti3.95In0.05O12 (YCTInO) having giant dielectric constant was prepared by the flame synthesis method using metal nitrate and solid TiO2 in ethylene glycol mono-methyl ether. X-ray powder diffraction (XRD) study on the material sintered at 1,050°C for 15 h reveals the single phase cubic perovskite structure. In Fourier transform infrared (FT-IR) spectroscopy, absorption bands were observed at 583 and 521 cm-1 corresponding to vibrations of Cu-O and 441 cm-1 of Ti-O-Ti, which are confirmed the single phase formation. X-ray photoelectron spectroscopy (XPS) data of YCTInO reveal the presence of Y 3d, Cu 2p, Ti 2p, In 3d, and O1s peaks of the elements, which justify the energy dispersive X-ray spectroscopy (EDX) results and compositional purity of the materials synthesized by the flame synthesis. The dielectric property of this material was studied in the frequency range of 0.01-100 kHz and the temperature range from 298 to 440 K. The electrical behavior of the ceramic studied by impedance and modulus spectroscopy reveal that the dielectric permittivity (ϵr) values of the YCTInO were dominantly affected by the electrical properties of grain-boundary. © 2016 Taylor & Francis Group, LLC.