• 한국세라믹학회지
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• 제25권6호
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• pp.694-698
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• 1988

Pb(Zr, Ti)O3-Pb(Co, Nb)O3 systems were investigated by x-ray diffraction method. System contains rhombohedral, tetragonal, and pseudocubic structures at room temperature. Crystal symmetry was changed from 4-fold symmetry to 3-fold symmetry by substituting Pb(Co1/3, Nb2/3)O3 ; PCN, to Pb(Zr0.52, Ti0.48)O3 ; PZT. As the substituted PCN concentration was increased, an increase in a-axis direction and a decrease in c-axis in the perovskite structure were occurred simultaneously, so that the crystal symmetry was changed into such way. In the higher sinteringtemperatures, the unit cell distortions occurred rather in the lower substitution range of PCN. The ferroelectric properties were maximized at the region that tetragonal and rhombohedral or pseudocubic structures were coexist.

• Transactions on Electrical and Electronic Materials
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• 제12권2호
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• pp.64-67
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• 2011

The effect of Ta substitution on the crystal structure, ferroelectric, and piezoelectric properties of $Bi_{0.5}(Na_{0.82}K_{0.18})_{0.5}Ti_{1-x}Ta_xO_3$ ceramics has been investigated. The Ta doping resulted in a transition from coexistence of ferroelectric tetragonal and rhombohedral phases to an electrostrictive pseudocubic phase, leading to degradations of the remnant polarization, coercive field, and piezoelectric coefficient $d_{33}$. However, the electricfield-induced strain was significantly enhanced by the Ta substitution-induced phase transition and reached a highest value of $S_{max}/E_{max}$ = 566 pm/V under an applied electric field 6 kV/mm when 2% Ta was substituted on Ti sites. The abnormal enhancement in strain was attributed to the pseudocubic phase with high electrostrictive constants.

• 센서학회지
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• 제30권6호
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• pp.408-414
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• 2021

This study analyzes the phase transition behavior and electrical properties of lead-free (1-x)K_0.5Na_0.5NbO₃-xBaZrO₃ (KNN-100xBZ) piezoelectric ceramics. The stabilized crystal structures in BaZrO₃-modified KNN ceramics is clarified to be pseudocubic. The polymorphic phase transition from the orthorhombic to pseudocubic phases can be observed with KNN-6BZ ceramics considering the optimized piezoelectric constant (d₃₃). Electromechanical strain behaviors are discussed. Accordingly, the enhancement of strain value at x = 0.08 (composition) may originate from the coexistence of ferroelectric domains and polar nanoregions. A schematic of domains for KNN, KNN-8BZ, and KNN-15BZ ceramics has been proposed to describe the relationship between the stabilized relaxor and changes in electrical properties.

• 대한화학회지
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• 제38권11호
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• pp.785-791
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• 1994

$Sr_1-_xY_xMnO_3$ (x = 0.0∼1.0)을 citrate법으로 합성하고 조성에 따른 구조적 전기적 성질의 변화를 알아보았다. X-ray diffraction method에 의해 각 산화물의 구조를 결정한 결과, $Sr_1-_xY_xMnO_3$ (x = 0.0∼1.0) system은 조성에 따라 4L-hexagonal perovskite(x = 0.0∼0.3) 구조, rhombohedral perovskite(x = 0.3∼0.7)구조를 거쳐 hexagonal nonperovskite(x=0.7∼1.0) 구조까지 3가지의 다른 결정구조를 갖는 것으로 관찰되었다. 이러한 $Sr_1-_xY_xMnO_3$ system의 구조 변화는 yttrium 양이 증가함에 따라 cell parameter가 증가하는 경향을 보였으며, 이는 $Mn^{4+}$ 대신 $Mn^{3+}$가 증가함에 따른 것으로 믿어진다. $SrMnO_3$의 $Sr^{2+}$ 자리에 $Y^{3+}$를 치환할수록 conductivity가 크게 증가하는 것이 관찰되었다. 4L-hexagonal구조를 갖는 $Sr_{0.9}Y_{0.1}MnO_3$와 pseudocubic perovskite 구조를 갖는 $Sr_{0.5}Y_{0.5}MnO_3$의 온도에 따른 전기저항 측정결과, $Sr_{0.9}Y_{0.1}MnO_3$에서 더 큰 energy gap을 갖는 것으로 관찰되었으며, 이 결과는 4L-hexagonal구조가 metal-metal 결합에 의해 안정화되어 있기 때문인 것으로 설명된다.

• 한국세라믹학회지
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• 제49권3호
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• pp.253-259
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• 2012

In this study, crystal structural changes and dielectric properties of $(1-x)Pb(Yb_{1/2}Nb_{1/2})O_3-xPbTiO_3$ ((1-x)PYN-xPT) solid solutions were measured and analyzed with respect to the $PbTiO_3$ (PT) contents ($0.40{\leq}x{\leq}0.60$). From X-ray diffraction (XRD) measurements, (1-x)PYN-xPT solid solutions showed changes of the crystal structure from pseudocubic ($0.40{\leq}x{\leq}0.44$) to tetragonal ($0.52{\leq}x{\leq}0.60$) on increasing PT contents and exhibited the coexistence of pseudocubic and tetragonal phase near the morphotropic phase boundary (MPB) composition ($0.46{\leq}x{\leq}0.50$). The dielectric constant showed a maximum value at x = 0.46 and the maximum values in (1-x)PYN-xPT decreased with higher PT contents. The phase transition temperatures of (1-x)PYN-xPT solid solutions increased over the whole composition ranges tested ($0.40{\leq}x{\leq}0.60$).

• 한국세라믹학회지
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• 제49권3호
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• pp.266-271
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• 2012

The effect of $Bi(Mg_{1/2}Sn_{1/2})O_3$ (BMS) modification on the crystal structure, ferroelectric and piezoelectric properties of $Bi_{1/2}(Na_{0.8}K_{0.2})_{1/2}TiO_3$ (BNKT) ceramics has been investigated. The BMS-substitution induced a transition from a ferroelectric (FE) tetragonal to a nonpolar pseudocubic phase, leading to degradations in the remnant polarization, coercive field, and piezoelectric coefficient $d_{33}$. However, the electric-field-induced strain was significantly enhanced by the BMS substitution-induced phase transition and reached a highest value of $S_{max}/E_{max}$ = 633 pm/V under an applied electric field of 6 kV/mm when the BMS content reached 6 mol%. The abnormal enhancement in strain was attributed to the field-induced transition of the pseudocubic symmetry to other asymmetrical structure, which was not clarified in this work.

• 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.

• 한국진공학회지
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• 제3권3호
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• pp.355-359
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• 1994

Cd1-xCoxIn2Se4(X=0.50) 결정을 수직 Bridgman 방법으로 성장시키고 성장된 결정의 결정구조 및 XPS 특성을 연구하였다. 성장된 결정은 pseudocubic 구조이고 격자상수는 a=5.778$\AA$으로 주어졌다. Cd1-xCoxIn2Se4 결정의 각 성분원소인 cadmium cobalt indium 그리고 selenium에 대한 XPS spectrum으 로부터 결합에너지와 결합상태를 조사하였다. Cd1-xCoxIn2Se4결정과 결합하지 안는 각 성분원소인 cadium cobalt imdium 그리고 selenium에 대한 core level의 XPS spectrum과 비교하면 각 성분원소상 이의 결합에 의한 chemical shift 현상 때문에 core level의 결합에너지가 0.10~4.87 eV 차이가 있다. Cd1-xCoxIn2Se4 결정에서 Co 2P3/2 core level의 주 peak와 statellite peak와의 결합에너지 차이로부터 cadmium과 치화된 cobalt는 Co2+ ion으로 Td symmetry 점에 위치함을 알 수 있다.

• 한국전기전자재료학회논문지
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• 제19권2호
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• pp.176-180
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• 2006

[ $(Na_{0.5}Bi_{0.5})TiO_3$ ][NBT] thin films were prepared on a highly (100) oriented $LaNiO_3[LNO]$ by sol-gel process. X-ray diffraction patterns of the NBT films annealed above $600^{\circ}C$ for 5 minutes have confirmed a highly (100) oriented growth and pseudocubic structure (a=3.884${\AA}$). The (l00) orientation factor increased from 90 to $99\%$ with increasing soaking time from 5 to 60 minutes at $600^{\circ}C$. The NBT films ($600^{\circ}C$/5 min,) have a flat and dense microstructure with large columnar grains, and their grain size are about 44 nm. The Au/NBT/LNO/Si hetero structure sample show a ferroelectric properties.

• 한국전기전자재료학회논문지
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• 제17권8호
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• pp.859-865
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• 2004

LaNiO$_3$(LNO) thin films on (100) Si substrates are prepared by sol-gel method on heat treatment conditions, such as heat transfer direction, pyrolysis and annealing process, and annealing temperatures and times. The effect of heat treatment conditions on the (100) orientations, structures and resistances of the thin films are investigated by XRD, SEM(FESEM), and a lout probe method. Highly (100) orientation factor(0.97), a pseudocubic crystalline structure with a dense and uniform microstructure could be formed by the following conditions： 1) the heat transfer direction is from Si substrate to LNO, 2) the pyrolysis and annealing process are alternated, 3) the annealing temperature is $650^{\circ}C$ and 4) the annealing times is 3 minutes. The sheet resistance of thin films decreased with increasing of a annealing temperature and time, and a number of coating.