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변재덕,현준원,김연중,Krist of Bobor 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.72 No.6
In this study, lead-free (K0.5Na0.5)1−xAg x NbO3 (x = 0.00, 0.10, 0.15, 0.20, 0.25, and 0.30) ferroelectric ceramics were fabricated using solid-state synthesis without A-site and B-site manufacturing step. The (K0.5Na0.5)1−xAg x NbO3 ceramics were sintered at 1110 °C for 4 h after calcination at 800 °C for 3 h. The sintered sample was dense, and the grain size was 1.02 ~ 7.8 μm. For x ≤ 0.2, the sintered ceramic samples had a single perovskite structure. The temperature dependence of the dielectric constant in the (K0.5Na0.5)1−xAg x NbO3 was measured at 1 kHz using an LCR meter. The high dielectric constant properties could be obtained in (K0.5Na0.5)1−xAg x NbO3 ceramics. The orthorhombic-to-tetragonal phase transition temperature and ferroelectric Curie temperature decreased linearly with increasing mole fraction of the Ag content. The Curie temperature shifted from 393 °C for (K0.5Na0.5)NbO3 ceramics to 317 °C for (K0.5Na0.5)0.7Ag0.3NbO3 ceramics. The maximum dielectric constant was 8930 at 330 °C in the (K0.5Na0.5)0.8Ag0.2NbO3 ceramics.
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현준원,변재덕,김연중 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.7
Complex perovskite Pb(Sc1/2Nb1/2)O3 ceramics were prepared under three different conditionsby using the conventional mixed oxide method. Sintering under different conditions resultedin complete formation of the perovskite phase in all of the samples. The microstructure ofPb(Sc1/2Nb1/2)O3 was observed by using field-emission scanning electron microscopy (FE-SEM). Raman spectra and the dielectric constant as functions of the temperature were measured. Ramanspectra showed a shift to lower frequencies of the F2g O-B-O symmetrical bending mode andchanges in the intensities and the line widths of the dirty modes with increasing sintering temperature. Also, at low wavenumbers (180 to 400 cm−1), significant changes were observed due toincreasing structural distortion with increasing sintering temperature. At approximately the Curetemperature (Tc), a phase transition of the sintered Pb(Sc1/2Nb1/2)O3 samples occurred over abroad range of temperatures.
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강유전체(K<SUB>0.5</SUB>Na<SUB>0.5</SUB>)NbO₃의 제조 및 전기적 특성 분석
현준원(June Won Hyun),변재덕(Jaeduk Byun) 한국표면공학회 2017 한국표면공학회지 Vol.50 No.4
Ferroelectric ceramics are broadly used for various industrial applications. In this research, the lead-free ferroelectric ceramics of (K0.5Na0.5)NbO₃ was fabricated by using the solid state synthesis. The (K0.5Na0.5)NbO₃ pellets were sintered at 1200, 1150 and 1100 ℃ for 4 hours in air atmosphere. Field-emission scanning electron microscopy (FE-SEM) characterization of the sintered KNN ceramics revealed surface morphology and grain size. And we used the X-ray diffraction (XRD) for measuring the sample crystal phase. Temperature dependence of the dielectric constant was measured by using an LCR meter. The sintered at 1150 ℃ for 4 hours sample has a highest dielectric constant 6011 at Curie temperature (TC) and dense structure with 2.33 μm grain size.
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Ferroelectric and Dielectric Properties of the Pb(Sc1/2Nb1/2)O3 Ceramic System
현준원,김연중,김강배,이기암,변재덕 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.3
This study examined the temperature dependence of the dielectric properties at various frequencies in the Pb(Sc1/2Nb1/2)O3(PSN) ceramic system with a perovskite structure produced using oxide mixing methods after sintering at 1420 ℃ for 15 minutes and at 1350 ℃ for 25 minutes. The ferroelectric properties of the PSN ceramic system were examined from the temperature dependence of the hysteresis loop by using a slight modification of the Sawyer-Tower circuit. The perovskite (1 1 0) to pyrochlore (2 2 2) ratio was determined by using X-ray diffraction, and the grain size of the sintered pellet was measured by field-emission scanning electron microscopy. The formation of sintered PSN was analyzed by energy dispersive X-ray spectroscopy.
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