• Title/Summary/Keyword: $Sr_2Fe_2O_5$

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Fe doped $SrTiO_3$ single crystal growth and its electrical conductivity (Fe를 첨가한 $SrTiO_3$ 단결정 성장과 전기전도도 조사)

  • Jeon, Byong-Sik;Cho, Hyun;Orr, Keun-Ho
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.5 no.3
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    • pp.209-214
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    • 1995
  • Abstract 0.2 wt % $Fe_2O_3$ doped $SrTiO_3$ single crystals were grown by floating zone method in air and Nz atmosphere, respectively. The growth rate was fixed at 5 mm/hr and rotation speed was maintained at 30 rpm. As - grown crystals were cut perpendicular to its growth direction and then, annealed at 900, 1000 and $1100^{\circ}C$ for 2 hours in Nz atmosphere. Resistivities of each samples were measured and then converted into conductivities. By using these conductivity values, the activation energies were calculated and by means of the calculated activation energies, mechanism which contribute to increasing the electrical conductivity were investigated.

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Properties of Synthesis (BaSr)$(CoFe)O_3$ Cathode for IT-SOFC by GNP (GNP 법을 이용한 저온형 SOFC용 (BaSr)$(CoFe)O_3$ 공기극의 제조 및 특성 평가)

  • Lee, Mi-Jai;Moon, Ji-Woong;Kim, Sei-Ki;Ji, Mi-Jung;Hwang, Hae-Jin;Lim, Yong-Ho;Choi, Byung-Hyun
    • 한국신재생에너지학회:학술대회논문집
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    • 2006.06a
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    • pp.51-54
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    • 2006
  • Cathode material, $(Ba_{0.5}Sr_{0.5})_{0.99}Co_{0.8}Fe_{0.2}O_{3-{\delta}}$, for low temperature SOFC was prepared by the glycine-nitrate synthesis process (GNP). The characteristics of the synthesized powders were studied with controlling pH of a precursor. The synthesis BSCF powders with pH were agglomeration state and calcinations temperature has not influence on particles. Highly acidicprecursor solution increased a single phase forming the temperature. Also, synthesis BSCF powder was show result for thermal analysis and alteration of difference crystal with pH. It is considered that Ba and Sr cannot complex by carboxylic acid group of glycine, because under highly acidic condition the caboxylic group mainly combined with $H^+$ insead of alkali and alkaline earth cations. In case of using precursor solution with pH $2{\sim}3$, a single perovskite phase was obtained at $1000^{\circ}C$. Polarization resistance of $(Ba_{0.5}Sr_{0.5})_{0.99}Co_{0.8}Fe_{0.2}O_{3-{\delta}}$ was measured by AC impedance spectroscopy from the two electrode symmetric cell. Area specific resistance of the $(Ba_{0.5}Sr_{0.5})_{0.99}Co_{0.8}Fe_{0.2}O_{3-{\delta}}$ air electrode at $500^{\circ}C\;and\;600^{\circ}C$ were $0.96{\Omega}?cm^2$ and $0.16{\Omega}?cm^2$, respectively.

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Mossbauer Studies of the $H_2$ Reduction Effects On Magnetic Properties of Sr-Ba Substituted Hexgonal Ferrite (치환형 Sr-Ba 육방 페라이트들의 자기적 성질에 수소환원이 미치는 효과에 관한 Mossbauer 분광학적 연구)

  • 박재윤;권명회;이재광
    • Journal of the Korean Magnetics Society
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    • v.9 no.1
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    • pp.35-40
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    • 1999
  • Sr substituted materials for some barium in M-type barium ferrite powder and Co-Ti substituted Sr-Ba hexagonal ferrite powder were prepared by citrate sol-gel method and 2 MOE sol-gel method these hexaferrite particles were reduced for 1hr in the hydrogen gas. The reduction temperatures were varied in the range of 250 $^{\circ}C$ to 500 $^{\circ}C$. X-ray diffraction patterns were measured using diffractometer with Cu $K_{\Alhpa}$ radiation. Mossbauer absorption spectra were measured with a constant acceleration spectrometer. We have focused on studying the origin of increasing $M_s$ by M$\"{o}$ssbauer spectroscopy. Ferrite particles which were sintered at 105$0^{\circ}C$ were found to be typical magnetoplumbite structure and single phase. XRD patterns with varying the reduction temperatures in $Sr_{0.5}Ba_{0.5}Fe_{10}O_{19}$ indicates ferrites particles become composite hexaferrites containing $\alpha$-Fe at T_{red}=350 \;$^{\circ}C$$. On the otherhand, it was found that $Co^{2+}$ ions and $Ti^{4+}$ ions in $Sr_{0.7}Ba_{0.3}Fe_{10}CoTiO_{19}$ prevent from changing $Fe^{3+}$ ions to $\alpha$-Fe during the $H_2$ reduction. Comparing Mossbauer results with XRD results, we have determined most of $\alpha$-Fe are reduced from $4f_{vi}$ sites and 12k sites of $Fe^{3+}$ ions. These $\alpha$-Fe phase bring the induced anisotropy and increase saturation magnetization $M_s$.TEX>.

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Studies on the Electrical Properties of $Dy_{2-x}Sr_{1+x}Fe_2O_{7-y}$ ferrite System Which Can be used as Filler for Conducting Rubbers (도전성 고무의 충전제로 이용 가능한 $Dy_{2-x}Sr_{1+x}Fe_2O_{7-y}$ 페라이트계의 전기적 특성에 대한 연구)

  • Lee, Eun-Seok;Choi, Sei-Young
    • Elastomers and Composites
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    • v.28 no.2
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    • pp.103-107
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    • 1993
  • To make new filler for conducting rubber, the sample of perovskite-related ferrite system $Dy_{2-x}Sr_{1+x}Fe_2O_{7-y}$ (x=0.0, 0.5, 1.0, 1.5, and 2.0) were synthesized at 1473K in air. $M{\ddot{o}}ssbauer$ spetrum of x=0.0 sample shows typical six line pattern with $M{\ddot{o}}ssbauer$ parameters, $I.S=3.6{\times}10^{-1}mm/sec,\;E_Q=-7.0{\times}10^{-2}mm/sec,\;H_{int}=5.19{\times}10^2\;Koe$. In case of x=2.0, the spectrum is composed of single line exhibiting coexistance of $Fe^{3+}(I.S.=3.7{\times}10^{-1}mm/sec)$ ions and $Fe^{4+}(I.S.=-1.9{\times}10^{-1}mm/sec)$ ions. With increase in x value electrical conductivity at constant temperature sharply increased and the activation energies decreased from $3.8{\times}10^{-1}\;to\;1.9{\times}10^{-1}\;eV$.

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A Study on the Effects of first and second additives Magnetic Characteristics of Anisotropic $SrO-5.7Fe_2O_3$. (1,2차 첨가제가 이방성 $SrO-5.7Fe_2O_3$의 자기적 특성에 미치는 효과)

  • Song, Joon-Tae;Shin, Yeong-Duck;Jeong, In-Young;Jin, Hong-Bum
    • Proceedings of the KIEE Conference
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    • 1990.07a
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    • pp.239-242
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    • 1990
  • The effect of $CaCo_3$, $SrCo_3$, $SiO_2$ and $H_3BO_3$ in the range of 0.1-1.0 wt% on strontium ferrites consisting of the magnetoplumbite phase $SrO-5.7Fe_2O_3$ were investigated. The hysteresis loop, density, demagnetization curve and the intrinsic coercive force were measured on anisotropic ferrite. The particle diameter and 0.5(wt%) of second additive $CaCo_3$ is particularly important for the properties of anisotropic ferrite. When the particle diameter is decreased from 1.98(${\mu}m$) to 1.07(${\mu}m$), the remance is increased from 2900 to 4010(G) and the coercive force from 2150 to 2850(Oe) at a sintering temperature 1230 ($^{\circ}C$). Remance Br(G), coercleve force(Oe) and maximum energy product of sample A-16 are87(%), 56(%), 67(%) of S-W model theoretical value.

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Electrical Characteristics of $SrTiO_3$ films by acceptor doping (불순물 주입에 의한 $SrTiO_3$ 박막의 전기적 특성 개선)

  • Park, Chi-Sun
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.7 no.2
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    • pp.334-340
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    • 1997
  • Electric and dielectric properties of the $SrTiO_3$films have been studied. The influence of impurities on $SrTiO_3$ films was evaluated to reduce the leakage current density. Acceptor doping, with a small concentration of Fe or Cr, has led to a substantial improvement to $10^{-9}$ order in the leakage current density. The experimental results can be explained by a model in which oxygen vacancies are the key defects responsible for the leakage current. The $SrTiO_3$ film 200 nm in thickness with 5 mol% excess SrO fabricated in $Ar/O_2$ at $550^{\circ}C$ obtained the lowest leakage current density $1.0 {\times} 1.0 A/\textrm{cm}^2$. The improved results can be introduced into the capacitor dielectric of giga bit DRAM memories.

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Preparation of Perovskite-Type Oxide (La1-xSrxCo1-yFeyO3-δ) Coating Solution by Sol-Gel Method (Sol-Gel법에 의한 Perovskite-Type Oxide(La1-xSrxCo1-yFeyO3-δ) 코팅용액의 제조)

  • Park, Ja-Ryong;Lee, Dong-Il;Jung, Sang-Hyeok;Kim, Tae-Hwan;Sung, Jae-Suk;Song, Ki-Chang
    • Korean Chemical Engineering Research
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    • v.43 no.6
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    • pp.740-744
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    • 2005
  • Perovskite-type oxide $La_{1-x}Sr_xCo_{1-y}Fe_yO_{3-{\delta}}$ sols were prepared by sol-gel method using $La(NO_3)_3{\cdot}xH_2O$, $Sr(NO_3)_2$, $Co(NO_3)_2{\cdot}6H_2O$ and $Fe(NO_3)_3{\cdot}9H_2O$ as starting materials. The properties of the perovskite-type oxide sols were investigated by viscometer, FT-IR, TG-DTA and XRD. The prepared sols showed 1.16 cp in average viscosity, and a strong acidic condition of pH 0.5, irrespective of composition of the starting materials. The viscosity of sols at the same volume decreases, but the gelation time of sols, at which the sol viscosity increases rapidly, increases when increasing La concentration in composition of starting materials.

The Study on Microstructure and Magnetic Properties of Ferrite with Various Fe Contents in $Mg_{1.9-2x}Mn_{0.05}Fe_{4x}O_{4+${\gamma}$}+2_{wt%} Al_2O_3$ ($Mg_{1.9-2x}Mn_{0.05}Fe_{4x}O_{4+${\gamma}$}+2_{wt%} Al_2O_3$ 조성내 Fe량 변화에 따른 페라이트의 미세구조 및 자기적 특성 연구)

  • 김성재;정명득;강대석
    • Journal of the Korean Ceramic Society
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    • v.31 no.3
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    • pp.235-240
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    • 1994
  • The electric and magnetic properties of Mg1.9-2xMn0.05Fe4xO4+${\gamma}$+2wt% Al2O3, and its microstructure have been investigated as a function of ferrite composition (x=0.45, 0.5, 0.55). The microstructure turned out to be independent on the ferrite composition. The resistivity was decreased with increasing Fe contents, whereas the Curie temperature decreased. Saturation magnetization was varied from 1741 to 2022 G with composition, and squareness ratio (SR), coercive force (BHc) were decreased and increased with increasing Fe contents respectively, so the sample which SR and BHc were 0.97 Oe and 1.49 Oe can be attainable at x=0.45.

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Crystallographic and Magnetic Properties of a Perovskite La1/3Sr2/3FeO2.96 (페롭스카이트 La1/3Sr2/3FeO2.96의 결정학적 및 자기적 성질에 관한 연구)

  • Yoon, Sung-Hyun
    • Journal of the Korean Magnetics Society
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    • v.15 no.3
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    • pp.167-171
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    • 2005
  • Detailed aspects of the charge disproportionation (CD) transition for a polycrystalline $La_{1/3}Sr_{2/3}FeO_{2.96}$ were studied with the X-ray diffraction, $M\ddot{o}ssbauer$ spectroscopy, and SQUID magnetometer. The crystal structure was found to be rhombohedral with a space group R/3c. The lattice parameters were $a_R=5.4874\;\AA,\;and\;a_R=60.07^{\circ}$, respectively. $M\ddot{o}ssbauer$ spectra were taken within a wide range of temperature from 4.2 K up to room temperature. In the low temperature region, the spectra were comprised of two superimposed sextets which originated from $Fe^{3+}\;and\;Fe^{5+}$, respectively. This was the antiferromagnetic mixed valence state produced by the charges disproportionated into two different species. In the high temperature region, however, only a singlet from $Fe^{3.6+}$ was observed, indicating that it was a paramagnetic averaged valence state. The CD transition occurred in the temperature range from 175 K to 200 K, in which the two phases coexisted. The origin for the CD transition was explained by the thermally generated fast hopping of electrons. Hysteresis loop showed that there existed a strong antiferromagnetic interaction among magnetic ions. As the temperature increased thru the CD transition temperature, it was very likely that the interaction between $Fe^{3+}\;and\;Fe^{5+}$ was replaced by a more stronger one.

The development and the magnetic properties of sheet hexaferrite magnets (Hexaferrite 쉬트자석의 개발과 자기적 성질에 관한 연구)

  • 김철성;박승일;오영제
    • Journal of the Korean Magnetics Society
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    • v.5 no.4
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    • pp.281-286
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    • 1995
  • In order to study the effect of additives $SiO_{2}$ on the magnetic properties of hexaferrite sheet magnet, we used X-ray diffractometer, Mossbauer spectrometer, and VSM magnetometer. We have prepared $Ba_{0.25}Sr_{0.75}Fe_{12}O_{19}$ green sheets by the Dr. Blade method. Most of samples have a magnetoplurnbite crystal structure of typical M-type hexaferrite. The lattice parameters are found not to be affected by the addition of $SiO_{2}$. ${\alpha}-Fe_{2}O_{3}$ phase develops above $SiO_{2}$ 2.0 wt.%. Isomer shifts indicate that the valence of Fe ions is trivalent. Curie temperatures decrease slightly with increasing $SiO_{2}$ concentrations. It means that the $Si^{4+}$ subsitution for 12k-site $Fe^{3+}$ has an effect on the superexchange interactions Fe-O-Fe, which change the distance and the angle between cations and anions. It was suggested that ${\alpha}-Fe_{2}O_{3}$ phase results from the excessive Fe produced by subsituting $Si^{4+}$ for $Fe^{3+}$. Based upon the results of $Ba_{0.25}Sr_{0.75}Fe_{12}O_{19}$ added with $SiO_{2}$, we concluded that $H_{c}$, $M_{s}$ and $M_{r}$ depend more strongly on the microstructure chracteristics than on the cation substitution.

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