• The Korean Journal of Ceramics
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• 제2권2호
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• pp.76-82
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• 1996

PLZT ceramics having two nominal compositions, $Pb_{1-3x/2}La_xV_{x/2}(Zr_{03}Ti_{03})O_3$ and $Pb_{1-x}La_x(Zr_{0.2}Ti_{0.5})_{1-x/4}V_{x/4}O_3$ (V: vacancy) with x=0.00~0.30, were prepared. The physical, structural, and dielectric properties were investigated by X-ray diffraction, scanning electron microscopy, Raman spectroscopy, and measurements of bulk density and dielectric constant. The two series with A-stie and B-site vacancies showed different physical, structural, dielectric properties, and, specially, Curie temperature. In comparison to PLZT with B-site vacancies, PLZT with A-site vacancies showed high Curie temperatures and low maxima of dielectric constant. Consequently, it is evident that the properties of PLZT ceramics depend on the vacancy formula adopted as a batch composition in preparation.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 추계학술발표대회
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• pp.33.1-33.1
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• 2011

Strontium doped lanthanum manganite (LSM) with perovskite structure for SOFC cathode material shows high electrical conductivity and good chemical stability, whereas the electrical conductivity at intermediate temperature below $800^{\circ}C$ is not sufficient due to low oxygen ion conductivity. The approach to improve electrical conductivity is to make more oxygen vacancies by substituting alkaline earths (such as Ca, Sr and Ba) for La and/or a transition metal (such as Fe, Co and Cu) for Mn. Among various cathode materials, $LaSrMnCuO_3$ has recently been suggested as the potential cathode materials for solid oxide fuel cells (SOFCs). As for the Cu doping at the B-site, it has been reported that the valence change of Mn ions is occurred by substituting Cu ions and it leads to formation of oxygen vacancies. The electrical conductivity is also affected by doping element at the A-site and the co-doping effect between A-site and B-site should be described. In this study, the $La_{1-x}Sr_xMn_{0.8}Cu_{0.2}O_{3{\pm}{\delta}}$ ($0{\leq}x{\leq}0.4$) systems were synthesized by a combined EDTA-citrate complexing process. The crystal structure, morphology, thermal expansion and electrical conductivity with different Sr contents were studied and their co-doping effects were also investigated.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 춘계학술발표대회
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• pp.29.2-29.2
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• 2011

B-site substitution with isovalent and donor impurities was compared in terms of the piezoelectric properties of Bi-based ABO3 perovskite ceramics. X-ray diffraction study revealed that both impurities bring about degradation in their ferroelectric properties as well as piezoelectric characteristics. However, there existed a difference between the isovalent and heterovalent impurities that influence a phase transformation of ferroelectric anisotropic-to-electrostrictive pseudocubic symmetry. Based upon analyses including the crystal, microstructure, dielectric, ferroelectric properties, we believed that A-site vacancies in the ABO3 ceramic significantly contribute to a ferroelectric-nonpolar phase transition, which give rise to lead to a giant strains. The present paper will discuss the origin of giant strains in Bi-based perovskite ceramics.

• 한국재료학회지
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• 제29권3호
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• pp.150-154
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• 2019

This study investigates the effect of MnO2 and CuO as acceptor additives on the microstructure and piezoelectric properties of $0.96(K_{0.5}Na_{0.5})_{0.95}Li_{0.05}Nb_{0.93}Sb_{0.07}O_3-0.04BaZrO_3$, which has a rhombohedral-tetragonal phase boundary composition. $MnO_2$ and CuO-added $0.96(K_{0.5}Na_{0.5})_{0.95}Li_{0.05}Nb_{0.93}Sb_{0.07}O_3-0.04BaZrO_3$ ceramics sintered at a relatively low temperature of $1020^{\circ}C$ show a pure perovskite phase with no secondary phase. As the addition of $MnO_2$ and CuO increases, the sintered density and grain size of the resulting ceramics increases. Due to the difference in the amount of oxygen vacancies produced by B-site substitution, Cu ion doping is more effective for uniform grain growth than Mn ion doping. The formation of oxygen vacancies due to B-site substitution of Cu or Mn ions results in a hardening effect via ferroelectric domain pinning, leading to a reduction in the piezoelectric charge coefficient and improvement of the mechanical quality factor. For the same amount of additive, the addition of CuO is more advantageous for obtaining a high mechanical quality factor than the addition of $MnO_2$.

• 한국세라믹학회지
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• 제32권7호
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• pp.839-845
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• 1995

The structural and dielectric properties of Pb(Mg1/3Nb2/3)O3 ceramics substituted by Nd3+, La3+, K+ and Na+ were studied over 0~50 at.% substituent content. The 1 : 1 ordering behavior of Mg2+ and Nb5+ ions in the B site sublattice was observed in Nd3+-and La3+-modified compounds. The degree of ordering was increased with Nd3+, La3+ content in the compounds. But K+-or Na+-modified compounds did not exhibit the ordering behavior. This was explained by charge and size effect of A and B site cations and oxygen vacancies. As the mole fractions of substituent increased, the maximum values of dielectric constants were rapidly decreased and the phase transitions were broadened. Phase transition temperature was correlated with the covalency of A-O and B-O bonding.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1992년도 춘계학술대회 논문집
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• pp.133-136
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• 1992

Electrical resistivity and piezoelectric properties were investigated in Lead Zirconate-Titante(PZT) with Nb$_2$O$\sub$5/dopant, fabricated from conventional mixed-oxide powders and molten salt synthesis. The resistivity and electromechanical coupling factor(K$\sub$p/) were increased with increasing Nb content. The reason for increasing of the electrical resistivity below the Curie Temperature(TC). It is believed that the Curie Temperature(Tc). It is believed that the p-type electrical conduction in PZT is due to lead vacancies. The electromechanical coupling factor(K$\sub$p/) and piezoelectric constant d$\sub$33/ were improved. This behavior can be explained as a compensation effect and Nb$\^$5+/ can serve as a donar and contribute electrons to the conduction process. As a result, the optimized Nb$_2$O$\sub$5/ dopants on the PZT specimens were 0.75 wt%.

• 한국재료학회지
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• 제2권3호
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• pp.207-212
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• 1992

과잉의 CaO와 $TiO_2$를 각각 포함한 $CaTiO_3$의 결함구조를 평형상태의 전기전도도를 $85O^{\circ}C$와 $1050^{\circ}C$사이에서 산소분압의 함수로 측정하여 연구하였다. 과잉의 CaO는 A site와 B site에 나누어져서 용해되어 $Ca_{Ti}$"와 Vo", 결함을 생성하였으며, 과잉의 $TiO_2$는 $V_{Ca}$"과 Vo"을 생성했다. 평형상태의 전기전도도는 CaO 용해도 5000ppm과 $TiO_2$ 용해도 2000ppm을 각각 나타냈다. 과잉의 양이온에 의하여 생성된 산소공공은 이온전도를 하여 넓은 영역의 산소 분압에 무관한 전도도 최소값을 보였으며, 반대로 대전된 음이온 결함과 결함쌍은 관찰되지 않았다.온 결함과 결함쌍은 관찰되지 않았다.

• 한국결정성장학회지
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• 제5권3호
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• pp.233-239
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• 1995

$La_{1/3}NbO_3$와 $La_{1/3}TaO_3$의 대형 단결정을 적외선 용융대역법으로 제작하여 A-자리 공공이 유전 특성에 미치는 영향에 대하여 조사하였다. Weissenberg 및 Precession 사진에서 $La_{1/3}TaO_3$ 결정의 대칭성은 tetragonal 이며, 격자정수는 a $\approx$ 0.397, b $\approx$ 0.397, c $\approx$ 0.775이다. 유전이상은 $2/3La^{3+}$ 이온이 공공자리로의 이동에 기인한 것으로 추측하였다.

• 대한화학회지
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• 제21권5호
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• pp.320-329
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• 1977

p-Phenylenediamine dihydroperchlorate의 세포상수는 $a=4.79{\pm}0.02,\;b=9.03{\pm}0.02,\;c=7.12{\pm}0.03{\AA},\;{\alpha}=109.4{\pm}0.2,\;{\beta}=79.6{\pm}0.2,\;r=104.6{\pm}0.2^{\circ},\;Z=1$이며 공간군은 $P\={1}$이다. 구조는 Patterson 및 Fourier법으로 해석하였으며 block diagonal 최소자승법으로 정밀화하였따. 등경사 Weissenberg 사진들에서 얻은 387개의 관측된 반사에 대하여 R값은 0.13이었다. 이 물질의 결정구조에서 수소결합은 아미노기와 과염소산 이온 사이에서 이루어져 있으며 2가지 형이 있다. 첫째것은, 한개의 삼지형 N${\cdot}{\cdot}{\cdot}$O 수소결합이고, 둘째것은, 보통형의 2개의 N${\cdot}{\cdot}{\cdot}$O 수소 결합이다. 한개의 p-phenylenediamine 그룹은 실험오차 내에서 평면이며 12개의 과염소산이온에 결합되어 있다. 그중 10개의 과염소산이온은 수소결합으로 연결되어 있으며 2개는 van der Waals 힘들로 접촉되어 있다. 한개의 과염소산이온은 6개의 p-phenylenediamine과 4개의 과염소산이온에 의하여 둘러싸여 있따. 6개의 p-phenylenediamine 그룹 중 5개는 수소결합이 되어있고 나머지는 van der Waals 힘으로 접촉되어 있다.

• 한국세라믹학회지
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• 제41권8호
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• pp.623-627
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• 2004

Ba가 첨가된 LaBaGa $O_4$ 층상 perovskite의 생성상과 전도거동에 대해 고찰하였다. LaBaGa $O_4$의 La-site에 20at% 이하의 $Ba^{2＋}$ 이온을 첨가한 조성은 $K_2$Ni $F_4$구조 사방정 단일상을 형성하였다. 건조분위기에서 L $a_{0.8}$B $a_{1.2}$G $a_{3.9}$는 높은 산소분압영역에서 산소이온전도와 hole(p-type)전도의 혼합전도를 나타내었다. 수증기분위기에서는 수증기가 산소빈자리로 유입되어 proton전도가 발생되었으며, 온도가 낮아질수록 총전도에 대한 proton 전도도의 기여가 증가하여 35$0^{\circ}C$ 이하의 온도에서는 proton 전도가 지배적인 전도를 나타내었다. Proton 전도에 대한 활성화 에너지는 0.72 eV였다.