• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.4
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• pp.218-222
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• 2017

In this paper, in order to develop excellent composition ceramics for a piezoelectric energy- harvesting device, we synthesized $0.99(Na_{0.52}\;K_{0.443}\;Li_{0.037})(Nb_{0.883}\;Sb_{0.08}\;Ta_{0.037})O_3$ + $0.01(Sr_{0.95}Ca_{0.05})TiO_3$ + $0.3\;wt%\;Bi_2O_3\;+\;0.3\;wt%\;Fe_2O_3\;+\;0.3\;wt%\;CuO$ (abbreviated as NKN-SCT) ceramics with different sintering times, using the ordinary solid-state reaction method. The effect of sintering time on the microstructure and piezoelectric properties was investigated. The ceramics with the sintering time of 7 h have the optimum values of the piezoelectric constant ($d_{33}$), piezoelectric voltage constant ($g_{33}$), planar piezoelectric coupling coefficient (kp), mechanical quality factor (Qm), and dielectric constant (${\varepsilon}r$): $d_{33}=314[pC/N]$, $g_{33}=20.07[10^{-3}mV/N]$, kp = 0.442, Qm = 93, ${\varepsilon}r=1,768$, all being suitable for a piezoelectric energy-harvesting device.

• Proceedings of the Korean Magnestics Society Conference
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• 2011.06a
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• pp.7-8
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• 2011

Basically, the lattice mismatch between film and substrate can make those BiFeO3(BFO) films distorted with strain structure. BFO phase can be stabilized on LaAlO3(LAO) represents the example of a multiferroic with giant axial ratio. Its crystal structure is not strictly tetragonal, but tetragonal with a slight monoclinic distortion and related to the rotation of the oxygen octahedra. In this study, we show that phases with a tetragonal-like epitaxial BFO films can indeed be ferroelectric and also can be stabilized via epitaxial growth onto LAO. Recent reports on epitaxial BFO films show that the crystal structure changes from nearly rhombohedral ("R-like") to nearly tetragonal("T-like") at strains exceeding approximately -4.5%, with the "T-like" structure being characterized by a highly enhanced c/a ratio. While both the "R-like" and the "T-like" phases are monoclinic, our detailed x-ray diffraction results reveal asymmetry change from MA and MC type, respectively. By applying additional strain or by modifying the unit cell volume of the film by substituting Ba for Bi, the monoclinic distortion in the "T-like" MC phase is reduced, i.e. the system approaches a true tetragonal symmetry. There are two different M-H loops for $Bi_{1-x}Ba_xFeO_{3-{\delta}}$(BBFO) and BFO films on SrTiO3(STO) & LAO substrates. Along with the ferroelectric characterization, these magnetic data indicate that the BFO phase stabilized on LAO represents the first example of a multiferroic with giant axial ratio. However, there is a significant difference between this phase and other predicted ferroelectrics with a giant axial ratio: its crystal structure is not strictly tetragonal, but tetragonal with a slight monoclinic distortion. Therefore, in going from bulk to highly-strained films, a phase sequence of rhombohedral(R)-to-monoclinic ["R-like" MA-to-monoclinic, "T-like" MC-to-tetragonal (T)] is observed. This sequence is otherwise seen only near morphotropic phase boundaries in lead-based solid-solution perovskites (i.e. near a compositionally induced phase instability), where it can be controlled by electric field, temperature, or composition. Our results show that this evolution can occur in a lead-free, stoichiometric material and can be induced by stress alone. Those major results are summarized as follows ; 1) Ba-doping increases the unit cell volume, 2) BBFO on LAO can be fully strained up to x=0.08 as a strain limit (Fig. 1), 3) P(E) & M(H) properties can be tuned by the variation of composition, strain, and film thickness.

• Proceedings of the Korean Magnestics Society Conference
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• 2006.11a
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• pp.96-97
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• 2006

• Proceedings of the Korean Magnestics Society Conference
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• 2014.05a
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• pp.31-31
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• 2014

• Proceedings of the Korean Magnestics Society Conference
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• 2014.05a
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• pp.32-32
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• 2014

• Proceedings of the Korean Magnestics Society Conference
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• 2010.06a
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• pp.133-134
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• 2010

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.10
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• pp.892-896
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• 2003

In this study, microstructure and piezoelectric properties of PSN-PZT ceramics modified with BiFeO$_3$ were investigated as a function of PNW substitution. With the increase of PNW substitution, tetragonality, Curie temperature and mechanical quality factor were decreased but grain size and electromechanical coupling factor(kp) was gradually increased. At 4 mol[%] PNW substitution, maximum kp of 0.567 was obtained.

• Proceedings of the Korean Magnestics Society Conference
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• 2016.05a
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• pp.112-112
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• 2016

• Journal of the Korean Ceramic Society
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• v.49 no.6
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• pp.485-492
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• 2012

Dense and single phase $BiFeO_3$ (BFO) ceramics were prepared using attrition milled calcined (coarse) powders of an average particle size of ${\approx}3{\mu}m$ by conventional sintering process. A relative density of ${\approx}96%$ with average grain size $7.3{\mu}m$ was obtained when the powder compacts were sintered at $850^{\circ}C$ even for a shorter duration of 10 min. In contrast, densification barely occurred at $800^{\circ}C$ for up to 12 h rather the microstruce showed the growth of abnormal grains. The grain growth behavior at different temperatures is discussed in terms of nonlinear growth rates with respect to the driving force. The sample sintered at $850^{\circ}C$ for 12 h showed enhanced electrical properties with leakage current density of $4{\times}10^{-7}A/cm^2$ at 1 kV/cm, remnant polarization $2P_r$ of $8{\mu}C/cm^2$ at 20 kV/cm, and minimal dissipation factor (tan ${\delta}$) of ~0.025 at $10^6$ Hz. These values are comparable to the previously reported values obtained using unconventional sintering techniques such as spark plasma sintering and rapid liquid phase sintering.

• Economic and Environmental Geology
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• v.34 no.1
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• pp.39-53
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• 2001

Environmental pollution of the Tohyun mine creek area was investigated on the basis of geology, mineralogy and geochemistry. In soils and sediments of the mine area, ${Al_2}{O_3}/{Na_2O}$ and ${K_2}O/{Na_2}O$ ratios are partly negative correlation against ${SiO_2}/{Al_2}{O_3}$, respectively. Geochemical characteristics of some trace and rare earth elements such as V/Ni, Ni/Co, La/Ce, Th/Yb, Th/U, La/Th, ${La_N}/{Yb_N}$, La/Sc and Sc/Th are revealed a narrow range and homogeneous compositions may be explained by simple source lithology. These results suggest that sediments source of the host shale around the mine area could be originated by basic to intermediate igneous rocks. Mineral compositions of soil and sediment near the mine area were partly variable mineralogy, which are composed of quartz, mica, feldspar, chlorite, clay minerals and some pyrite. Soils and sediments with highly concentrated heavy minerals, gravity separated mineralogy, are composed of some pyrite, arsenopyrite, chalcopyrite, sphalerite, galena, goethite and various kinds of hydroxide minerals on the polished sections. As normalized by bed rock composition, average enrichment indices of major elements in sediments, precipitates, farmland soils and paddy soils are 1.0, 1.7, 0.9 and 0.8, respectively. Maximum concentration of environmental toxic elements in the mine creek are detected with Ag = 186 ppm, As = 17,100 ppm, Bi = ]27 ppm, Cd = 77 ppm, Cu = 12,299 ppm, Pb = 8,897 ppm, Sb = 1,350 ppm, W = 599 ppm and Zn = 12,250 ppm, which are increasing with total FeO increasing, and extremely high concentrations of surface sediments and precipitates near the waste rock dump. These toxic elements (As, Bi, Cd, Cu, Pb, Sb, W and Zn) of the samples, normalizing by host rock concentration, revealed that average enrichment index is 106.0 for sediments, 279.6 for precipitates, 3.5 for farmland soils and 1.6 for paddy soils. However, on the basis of EPA values, enrichment indices of all the samples are 40.7, 121.4, 1.3 and 0.6, respectively.