• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.4
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• pp.160-165
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• 2015

Lead-free piezoelectric materials have been actively studied to substitute for conventional PZT based solid solution, $Pb(Zr_xTi_{1-x}O_3)$, which occurs unavoidable PbO during the sintering process. Among them, Bismuth Sodium Titanate, $Na_{0.5}Bi_{0.5}TiO_3$ (abbreviated as NBT) based solid solution is attracted for the one of excellent candidates which shows the strong ferroelectricity, Curie temperature (Tc), remnant polarization (Pr) and coercive field (Ec). Especially, the solid solution of rhombohedral phase NBT with tetragonal perovskite phase has a rhombohedral - tetragonal morphotropic phase boundary. Modified NBT with tetragonal perovskite at the region of MPB can be applied for high frequency ultrasonic application because of not only its low permittivity, high electrocoupling factor and high mechanical strength, but also effective piezoelectric activity by poling. In this study, solid state ceramic processing of NBT and modified NBT, $(Na_{0.5}Bi_{0.5})_{0.93}Ba_{0.7}TiO_3$ (abbreviated as NBT-7BT), at the region of MPB using 7 % $BaTiO_3$ as a tetragonal perovskite was introduced and the structure between NBT and NBT-7BT were analyzed using rietveld refinement. Also, the ferroelectric and piezoelectric properties of NBT-7BT such as permittivity, piezoelectric constant, polarization hysteresis and strain hysteresis loop were compared with those of pure NBT.

• Journal of Electrochemical Science and Technology
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• v.10 no.3
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• pp.335-343
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• 2019

In this study, $Sr_2Ni_{1.8}Mo_{0.2}O_{6-{\delta}}$ (SNM) with a double perovskite structure was investigated as an alternative anode for use in the $CH_4$ fuel in solid oxide fuel cells. SNM demonstrates a double perovskite phase over $600^{\circ}C$ and marginal crystallization at higher temperatures. The Ni nanoparticles were exsolved from the SNM anode during the fabrication process. As the SNM anode demonstrates poor electrochemical and electro-catalytic properties in the $H_2$ and $CH_4$ fuels, it was modified by applying a samarium-doped ceria (SDC) coating on its surface to improve the cell performance. As a result of this SDC modification, the cell performance improved from $39.4mW/cm^2$ to $117.7mW/cm^2$ in $H_2$ and from $15.9mW/cm^2$ to $66.6mW/cm^2$ in $CH_4$ at $850^{\circ}C$. The mixed ionic and electronic conductive property of the SDC provided electrochemical oxidation sites that are beyond the triple boundary phase sites in the SNM anode. In addition, the carbon deposition on the SDC thin layer was minimized due to the SDC's excellent oxygen ion conductivity.

• Transactions of the Korean hydrogen and new energy society
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• v.33 no.2
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• pp.164-175
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• 2022

In this work, sulfonated poly (ether ether ketone) (SPEEK) composite membranes including strontium zirconate (SrZrO₃) were fabricated by the electrospinning method. Fourier-transform infrared spectroscopic analysis and X-ray diffraction analysis were used to identify the chemical structure and the crystallinity of SrZrO₃ and electrospun composite membranes. The thermal stability of the pure SPEEK and SPEEK/SrZrO₃ electrospun composite membranes were investigated by using thermogravimetric analysis. The physicochemical properties and proton conductivity were enhanced with the addition of different weight ratio of SrZrO₃ nanofiller (2, 4 and 6 wt%) in SPEEK polymer. The optimized SPEEK/SrZrO₃-4 electrospun membrane containing 4 wt% of SrZrO₃ showed a high proton conductivity compared to other electrospun SPEEK/SrZrO₃ composite membranes. The results indicate that electrospun composite membranes incorporating these perovskite nanofillers should be explored as potential candidates for use in proton exchange membrane fuel cells.

• Proceedings of the Materials Research Society of Korea Conference
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• 1997.10a
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• pp.34-34
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• 1997

• Journal of the Korean Ceramic Society
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• v.36 no.11
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• pp.1139-1142
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• 1999

• Journal of the Mineralogical Society of Korea
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• v.14 no.1
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• pp.73-84
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• 2001

티타늄과 산소의 함량이 서로 다른 4가지의 합성 페롭스카이트형(perovskite-type) 광물(($K_2$$La_2$$Ti_{n}$/$O_{2n+4}$, n=3, 4, 5, 6; 14/mcm, 14/mmm, I42 m)을 대상으로 리트벨트(Rietveld)구조분석법을 실시하여 결정구조를 밝히고 티타늄함량에 따른 층상형 구조를 연구하였다. 4가지 합성시료에 대하여 구조분석을 실시한결과 대표적인 페롭스카이트형 광물인 토소나이트(taustonite, $La_{1-x}$ //$K_{x}$ /$TiO_3$, x<0.4)가 주성분으로 나타났으며 토스나이트내에 12개의 산소를 배위하는 A자리 양이온은 자리점유율에 의해 $La^{3+}$ 와 $K^{+}$ /의 치환관계를 보여준다 공간군은 14/mcm, 단위포는 a=5.505(1)~5.510(1)$\AA$, c=7.793(1)~7.796(1)$\AA$ V=236.25~236.66 $\AA^3$ 범위의 값을 갖는다. 구조의 정밀도를 나타내는 R지수를 살펴보면 $R_{B}$ 값은 5.31~9.10 S(GofF)값은 0.86~1.24로 각각 계산되었다. 12배위를 하는 A자리 양이온인 란탄과 산소의 평균거리는 2.755$\AA$이고 6배위를 하는 B자리 양이온인 티타늄과 산소의 평균거리는 1.948 $\AA$의 결과를 얻었다. 합성된페롭스카이트형 광물의 층상구조가 알려져 있지 않아 시뮬레이션을 통해 구조모델을 결정하였으며 그결과 n=3인 R-38시료에서만 두 종류의 층상 페롭스카이트($La_2$$K_2$$Ti_3$$O_{10}$ ) 구조 (A-type: 14/mmm, a=3.8178 $\AA$, c=29.9189 $\AA$, V=436.04 $\AA^3$, B-type: 142 m, a =3.8376 $\AA$, c=28.023 $\AA$, V=412.6 $\AA^3$)가 존재함을 확인하였으나 다른 시료에서는 토소나이트, 금홍석 외에 새로운 합성광물로 제파이트의 존재를 확인하였다.

• Korean Journal of Materials Research
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• v.7 no.1
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• pp.33-39
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• 1997

Single phase pero~~skite lead lanthanum titanate thin films were fabricated on $Pt/Ti/SiO_2/Si$ substrates at the temperature of $480^{\circ}C$ by electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR PECVD) using metal organic sources $Pb(DPM)_2$ pre-flowing treatment in ECIi oxygen plasma before fabricating PLT films 11romote the perovskite nucleation due to stable supplying of the $Pb(DPM)_2$ and providing the F'h-rich atmosphere in the early stage of deposition. $Pb(DPM)_2$ pie-flonring treatment enhanced the properties of PLT films. The charactcristics of the PLT filrris were investigated as a tunction of the flow rate of Ti-source. The PL'i' films were grown in a perovskite structure tvith (100) preferred orientation. The high X-ray diffraction intensity and dielectric constant were obtained from the stoichiometric perovskite $(Pb,La)TiO_3$.

• KEPCO Journal on Electric Power and Energy
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• v.6 no.2
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• pp.157-161
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• 2020

Regarding greenhouse gas reduction, BIPV (Building Integrated Photovoltaics) is an important technology that can generate its own power in urban buildings based on clean energy resources. In particular, the perovskite material is attracting attention as a BIPV solar cell because it can have various colors and transparency. However, it is not easy to increase both transparency and efficiency factors because solar cell transparency and efficiency are inversely related to each other. Therefore, in this paper, we propose a semi-transparent perovskite solar cell structure that can improve both transparency and efficiency, and evaluate the stability according to international standard.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.12 no.1
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• pp.36-41
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• 2002

Abstract The stoichiometric and double-ordered perovskite $Sr_2FeMoO_6$ (SFMO) polycrystalline ceramics were fabricated by sintering at above $900^{\circ}C$ in $H_2$(5%)/Ar reductive ambient. SMO polycrystals showed good ferromagnetic properties andmagnetrotesistqnce ratios of about 15 % at 8K and 3 % at room temperature. Amorphous SFMO thin films were deposited on $LaA1O_3$ and $SrTiO_3$ single crystal substrates using rf sputtering method with the SFMO polycrystalline ceramic target. Double-ordered perovskite polycrystalline SFMO thin films were fabricated by solid state crystallization by annealing the deposited amorphous films at above $680^{\circ}C$ in $H_2$(5%)/Ar reductive ambient. SFMO thin films exhibited ferromagnetic behavior. Their magnetroresistance ratios, however, were only 0.3~0.5% at 8K and disappeared with increasing the measuring temperature. This was attributed to the absence of magnetic spin tunneling between grains due to the porous structure and non-stoichiometric composition of the deposited films.

• Journal of the Korean Ceramic Society
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• v.43 no.11 s.294
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• pp.715-723
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• 2006

Perovskite oxide materials are very important for the electronics industry, because they exhibit promising properties. With an interest in the obvious applications, significant effort has been invested in the growth of highly crystalline epitaxial perovskite oxide thin films in our laboratory. And the desired structure of films was formed to achieve excellent properties. $Y_1Ba_2Cu_3O_{7-x}$ (YBCO) superconducting thin films were simultaneously deposited on both sides of 3 inch wafer by inverted cylindrical sputtering. Values of microwave surface resistance R$_2$ (75 K, 145 GHz, 0 T) smaller than 100 m$\Omega$ were reached over the whole area of YBCO thin films by pre-seeded a self-template layer. For implementation of voltage tunable high-quality varactor, A tri-layer structured SrTiO$_3$ (STO) thin films with different tetragonal distortion degree was prepared in order to simultaneously achieve a large relative capacitance change and a small dielectric loss. Highly a-axis textured $Ba_{0.65}Sr_{0.35}TiO_3$ (BST65/35) thin films was grown on Pt/Ti/SiO$_2$/Si substrate for monolithic bolometers by introducing $Ba_{0.65}Sr_{0.35}RuO_3$ (BSR65/35) thin films as buffer layer. With the buffer layer, the leakage current density of BST65/35 thin films were greatly reduced, and the pyroelectric coefficient of $7.6\times10_{-7}$ C $cm^{-2}$ $K^{-1}$ was achieved at 6 V/$\mu$m bias and room temperature.