• 한국재료학회지
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• 제27권3호
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• pp.144-148
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• 2017

The effects of an excess of Bi on the piezoelectric and dielectric properties of $0.60Bi_{1+x}FeO_3-0.40BaTiO_3$ (x = 0, 0.01, 0.03, 0.05, 0.07) were investigated. The ceramics were processed through a conventional solid state reaction method and then quenched after sintering at different temperatures in the range of $980{\sim}1070^{\circ}C$. A single perovskite structure without any secondary phase was confirmed for all compositions and temperatures. It was found that excess Bi reduced the sintering temperatures, acted as a sintering aid and enhanced the properties in combination with quenching. Curie temperature ($T_C$) was found to slightly increase due to the presence of excess Bi; electrical properties were also improved by quenching. At x = 0.03 and $1030^{\circ}C$, remnant polarization ($2P_r$) was as high as $45.4{\mu}C/cm^2$ and strain at 40 kV/cm was up to 0.176 %.

• 한국자기학회지
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• 제15권2호
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• pp.137-141
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• 2005

Spinel계 유화물 $Zn_xFe_{1-x}Cr_2S_4$(x=0.05, 0.1, 0.2)에 대하여 X선 회절법, 자기저항측정, $M\ddot{o}ssbauer$ 분광법을 이용하여 CMR 특성과 자기적 성질을 연구하였다. 결정구조는 상온에서 입방정으로 정상 spinel 구조를 갖는 것으로 나타났다. 자기저항 실험결과 160K 부근 이하에서는 반도체적 전기전도 특성을 보이며, Curie 온도부근에서 최대자기저항 온도가 나타났다. Zn 조성값이 증가함에 따라 Jahn-Teller 효과에 의한 완화 현상이 증가되었으며, 전기 사중극자 이동값 역시 증가되고, 초미세 자기장값은 감소하였다. CMR 특성은 heterovalency에 의한 이중교환 상호작용이나, $Fe^{2+}$와 $Cr^{3+}$ 그리고 $Fe^{3+}$ 사이의 삼중교환 상호작용과는 다른 동적 Jahn-Teller 효과에 의한 도체-반도체전이와 절반 금속성 에너지 밴드구조에서 스핀전자 전이에 의하여 발생되는 것으로 예측된다.

• 한국자기학회지
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• 제17권1호
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• pp.30-33
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• 2007

[ $FeIn_2S_4$ ]를 제조하여 뫼스바우어 분광기, X-선 회절기, SQUID 자화율 측정기를 이용하여 결정학적 및 자기적 특성을 연구하였다. 결정구조는 역스피넬 구조로 In 이온은 각각 사면체 자리(A site)와 팔면체 자리(B site)에 동시에 존재하는데 비하여, Fe 이온은 팔면체 자리에만 존재하였다. Curie-Weiss 역자화율에 따른 유효자기모멘트는 $5.09{\mu}_B$였으며, 닐온도($N\'{e}el$ temperature)는 13 K였다. 이와 같이 낮은 닐온도는 팔면체 자리의 $Fe^{2+}(B)-S^2-Fe^{2+}(B)$의 초미세 상호작용이 약하기 때문인 것으로 설명되어진다. 전기사중극자 상호작용의 온도 의존성은 z-축에 따른 결정장 이론으로 설명되어진다.

• Journal of Magnetics
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• 제18권4호
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• pp.386-390
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• 2013

This paper studies the effects of A-site substitution by barium on the magnetic and magnetocaloric properties of $Pr_{0.5}Sr_{0.5-x}Ba_{x}MnO_{3}$ (x = 0, 0.04, 0.08 and 0.1). The tetragonal crystal structures of the samples are confirmed by room temperature X-ray diffraction. The dependence of the Curie temperature ($T_C$) and the magnetic entropy change (${\Delta}S_M$) on the Ba doping content has been investigated. The samples of all doping contents undergo the second order phase transition. As the concentration of Ba increased, the maximum entropy change ($|{\Delta}S_M|_{max}$) increased gradually, from 1.15 J $kg^{-1}$ $K^{-1}$ (x = 0) to 1.36 J $kg^{-1}$ $K^{-1}$ (x = 0.1), in a magnetic field change of 1.5 T. The measured value of $T_C$ is 265 K, 275 K, 260 K and 250 K for x = 0, 0.04, 0.08 and 0.1, respectively. If combining these samples for magnetic refrigeration, the temperature range of ~220 K and 290 K, where |${\Delta}S_M$|max is stable at ~1.27 J $kg^{-1}$ $K^{-1}$ and RCP = 88.9 $J{\cdot}kg^{-1}$ for ${\Delta}H$ = 1.5 T. $Pr_{0.5}Sr_{0.5-x}Ba_{x}MnO_{3}$ compounds, are expected to be suitable for magnetic-refrigeration application due to these magnetic properties.

• 대한화학회지
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• 제36권2호
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• pp.212-217
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• 1992

수용액내에서 gadolinium-벤조산 착물형성 반응의 열역학적 함수값들을 이온상수 0.1M $NaClO_4$, $25^{\circ}C$ 조건하에서 구하였다. gadolinium-벤조산 착물의 안정도는 여분의 엔트로피 효과에 기인하는 것으로 판단되며, 벤조산 리간드의 경우 한 자리 리간드에 비해 높은 안정도 상수값을 나타내었다. 이러한 높은 안정도는 리간드내의 벤젠고리의 공액효과로 예측되었다. 합성된 Ga$(ben)_3$의 고체 IR스펙트럼 결과, 벤조산 리간드가 두 자리 리간드로 작용하여 킬레이트를 형성하였으며, 80${\sim}$300K 온도 범위에서의 자화율 데이터는 Curie-Weiss 법칙에 잘 적용됨을 알 수 있었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
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• pp.52-52
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• 2008

The positive temperature coefficient of resistivity (PTCR) effect in (1-x)$BaTiO_3$ - $x(Bi_{0.5}K_{0.5})TiO_3$ doped with $Nb_2O_5$ was investigated. $(Bi_{1/2}K_{1/2})TiO_3$ (BKT) is more environment-friendly than $PbTiO_3$ in order to use in PTC thermistors. The incorporation of 1 mol% BKT to $BaTiO_3$ increased the Curie temperature (Tc) to $148^{\circ}C$. Doping of $Nb_2O_5$ to $Ba_{0.99}(Bi_{0.5}K_{0.5})_{0.01}TiO_3$ (BaBKT) ceramic has enhanced its PTCR effects. For the sample containing 0.025 mol% $Nb_2O_5$, it showed good PTCR properties; low resistivity at room temperature (${\rho}_r$) of 30 $\Omega{\cdot}cm$, a high PTCR intensity of approximately $3.3\times10^3$, implying the ratio of maximum resistivity to minimum resistivity (${\rho}_{max}/{\rho}_{min}$) in the measured temperature range, and a large resistivity temperature factor (a) of 13.7%/$^{\circ}C$ along with a high Curie temperature (Tc) of $167^{\circ}C$. In addition, the cooling rate of the samples during the sintering process had an influence on their PTCR behavior. All the samples showed the best ${\rho}_{max}/{\rho}_{min}$ ratio when they have cooled down at a rate of $600^{\circ}C$/min.

• Bulletin of the Korean Chemical Society
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• 제34권6호
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• pp.1679-1683
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• 2013

Intergrowth perovskite type complex oxides $La_{0.8}Ln_{0.2}Sr_2MnCrO_{7-{\delta}}$ (Ln=La, Nd, Gd, and Dy) have been synthesized by sol-gel method. Rietveld profile analysis shows that the phases crystallize with tetragonal unit cell in the space group I4/mmm. The unit cell parameters a and c decrease with decreasing effective ionic radius of the lanthanide ion. The magnetic studies suggest that the ferromagnetic interactions are dominant due to $Mn^{3+}$-O-$Mn^{4+}$ and $Mn^{3+}$-O-$Cr^{3+}$ double exchange interactions. Both Weiss constant (${\theta}$) and Curie temperature ($T_C$) increase with decreasing ionic radius of lanthanide ion. It was found that the transport mechanism is dominated by Mott's variable range hopping (VRH) model with an increase of Mott localization energy.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1991년도 추계학술대회 논문집 학회본부
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• pp.278-281
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• 1991

1) The specimen with 0.175[mol%] of additive $Sb_2O_3$ was minute and didn't appear porosity. The relation between the ratio of resistivity at $160^{\circ}C$ to that at $121^{\circ}C$ of the specimen with 0.175[mol%] of additive $Sb_2O_3$ was $3{\times}10^4$ and it's great value from among specimens. 2) The curie temperature of the specimen with 0.2 [mol%] of additive $Sb_2O_3$ was $140^{\circ}C$ AND it's great value from among specimens and those of other were $121^{\circ}C$ in all therefore, the specimen with above 0.2[mol%] of additive $Sb_2O_3$ is not match for PTCR 3) The variation of radiation properties of the specimen with 0.2[mol%] of additive $Sb_2O_3$ was very steep in the range of far-infrared $5{\sim}10[{\mu}m]$ but radiation percentage was very high of 0.92 in the range of $10[{\mu}m]$.

• 한국자기학회지
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• 제2권3호
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• pp.211-215
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• 1992

The temperature-dependent saturation magnetization curves of amorphous $Fe_{80-x}Co_xB_{20}$ (8 ${\le}$ x ${\le}$ 40, the step of x is 8) alloys were measured using a vibrating sample magnetometer from 77 K up to 1000 K. Curie temperature and the Bloch coefficient were estimated from the saturation magnetization curves. The low temperature dependence of magnetization is in good agreement with Bloch relation, $M_s(T)$=$M_s(O)$ (1-$BT^{3/2}$ - ${\cdots}.$). The spin wave stiffness constant, tne range of the exchange interaction, and the probable atomic spin were calculated from the saturation magnetization values.

• 한국세라믹학회지
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• 제25권5호
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• pp.488-494
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• 1988

Effects of MnO2 addition on themicrostructure, dielectric and piezoelectric properties of Rhombohedral, Tetragonal and Morphotropic phase boundary(MPB) in Pb(Ni1/3Nb2/3)O3-PbTiO3-PbZrO3 system were investigated and respectively the amount of MnO2 addition was 0, 0.2, 0.5, 1.0, 3.0wt%. In the tetragonal region, compared with the Rhombohedral and Morpotropic phase boundary, Mechanical quality factor(Qm), Curie temperature(Tc) and Dissipation factor were promoted by addition of MnO2. According to the results of the microstructure, dielectric and piezoelectric properties, the solid solution range of MnO2 addition in this system was 0.2-0.5wt%.