• Title, Summary, Keyword: Relaxor

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Direct Determination of Cationic Disordering in Sodium Bismuth Titanate

  • Choi, Si-Young;Ikuhara, Yuichi
    • Applied Microscopy
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    • v.42 no.3
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    • pp.164-173
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    • 2012
  • The relaxor ferroelectric feature in lead-free perovskite oxides, where the dipoles are randomly oriented and they can be feasibly aligned parallel to the external bias, is attracting lots of attention in the field of piezoelectric materials science, since it is one of candidates to replace the toxic lead-based materials that are still being commercially used. However, the origin of relaxor characteristic and its related atomic structure are still ambiguous. In this study, $Na_{1/2}Bi_{1/2}TiO_3$, chosen as a model relaxor system, was found to exhibit a cationic-disordered atomic structure; and furthermore the nonpolar atomic structure and its related oxygen tilting were ascertained via annular bright field imaging skill. We also found that this cationic disordering gives rise to the local formation of atomic vacancies.

Sr/Ba Ratio Dependence of Dielectric Characteristics in Strontium Barium NiobateCeramics (Sr/Ba 비에 따른 Strontium Barium Niobate 세라믹스의 유전특성)

  • 김명섭;이준형;김정주;이희영;조상희
    • Journal of the Korean Ceramic Society
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    • v.38 no.12
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    • pp.1167-1173
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    • 2001
  • The tetragonal tungsten bronze type of Sr$_{x}Ba_{1-x}Nb_{2}O_{6}$(SBN) (0.3$\le$x$\ge$0.7) ceramics was synthesized by the solid state reaction method, and the dielectric properties of SBN ceramics as a function of Sr/Ba ratio were examined. With increasing Sr/Ba ratio in SBN ceramics, the Curie temperature decreased and the maximum dielectric constant at the Curie temperature increased. The relaxor behavior of the SBN ceramics as a function of Sr/Ba ratio was quantitatively evaluated. More relaxor behavior of dielectric characteristics was observed as the ratio of Sr/Ba increased. The experimental results are explained with a viewpoint of crystallography of tungsten bronze structured SBN ceramics.

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Micro-Macro Domain Switching and Thermoelastic Martensitic Transformation in $PbZrO_3$-doped $Pb(Ni_{1/3}Nb_{2/3})O_3-PbTiO_3$ System ($PbZrO_3$가 첨가된 $Pb(Ni_{1/3}Nb_{2/3})O_3-PbTiO_3$ 계의 미소-거시 분역 반전과 열탄성 마르텐사이트 변태)

  • 윤만순;장현명
    • Journal of the Korean Ceramic Society
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    • v.32 no.9
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    • pp.967-976
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    • 1995
  • The possiblity of the existence of a spontaneous relaxor-normal ferroelectric transition was proposed and examined using 1~5 mol% PbZrO3-doped Pb(Ni1/3Nb2/3)O3-PbTiO3 (PNN-PT) systems having tetragonal symmetry at rom temperature. On cooling, the system with 60mol% Pb(Ni1/3Nb2/3)O3 underwent a spontaneous transition from a relaxor to a normal ferroelectric state. A microscopic examination demonstrates that the relaxornormal ferroelectric transition corresponds to a micro-macro domain switching accompanied with thermoelastic martensitic transformation. The long-range macrodomains below the transition temperature were characterized by twinlike 90$^{\circ}$macrodomains with tetragonal symmetry. The relaxor-normal ferroelectric transition was further correlated with the rhombohedral-tetragonal first-order structural transition.

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Effect of Poling Electric Field and Temperature Change on the Dielectric Anomalies of Relaxor Ferroelectric Strontium-Barium-Niobate Single Crystals

  • Shabbir, Ghulam;Ko, Jae-Hyeon;Kojima, Seiji
    • Journal of the Korean Physical Society
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    • v.73 no.10
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    • pp.1561-1565
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    • 2018
  • The dielectric properties of the uniaxial relaxor ferroelectric $Sr_xBa_{1-x}Nb_2O_6$ with x = 0.75 were investigated along the polar [001] direction as a function of temperature. The capacitance maximum showed the frequency dispersion commonly observed in relaxors. Additional weak dielectric anomalies were observed in the paraelectric phase; they were only seen during the heating process and disappeared upon subsequent cooling. These were attributed to the existence of large polar clusters strongly pinned at defects and/or to random fields and their metastable characters. Aligning the ferroelectric domains along the polar axis at room temperature removed the high-temperature dielectric anomalies. The dependences of the capacitance and the dielectric maximum temperature on the magnitude of the poling field were investigated.

Phase Transition and Relaxor Behaviors in the Lead Magnesium Niobate-based Ferroelectrics (Pb(Mg1/3Nb2/3)O3-based 강유전체의 상전이 및 완화특성)

  • Kim, Y.J.;Lee, J.H.
    • Journal of the Korean Vacuum Society
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    • v.17 no.2
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    • pp.148-155
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    • 2008
  • Dielectric and pyroelectric properties of relaxor ferroelectric in the PMN-PT solid solution series have been investigated. Features of the diffuse phase transition in PMN-PT system, typical relaxor ferroelectric materials, were studied as a function of temperature and frequency. The transition temperature of the ceramics with PT$\sim$0.325 did not depend on the measuring frequency. This can best realized in a relatively random environment that apparently is provided by PMN-rich complex perovskites, including those containing Pb. The composition with PT>0.35 show the characteristics of a normal single phase ferroelectric material. Thus the studies revealed that the morphotropic phase boundary in the PMN-PT system is in the vicinity of PT$\sim$0.3 and it has a small curvature and as a result the compositions near the morphotropic phase boundary show two phase transitions, rhombohedral$\rightarrow$tetragonal$\rightarrow$cubic, when the samples are heated up to higher temperature. The best optimum compositions are observed near the morphotropic phase boundary.

Ferroelectric Properties and DPT in the Perovskite PMT-PT System (Perovskite PMT-PT계의 강유전 특성 및 확산상전이)

  • Kim, Y.J.
    • Journal of the Korean Vacuum Society
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    • v.17 no.2
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    • pp.122-129
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    • 2008
  • Ferroelectric properties of the PMT-PT were also studied from the temperature dependence of hysteresis loops using a method slightly modified from Sawyer-Tower's. Dielectric, pyroelectric and piezoelectric properties of the ceramics in the system PMT-PT were investigated. The resulted densities of the PMT-PT ceramics system were greater than 97 % of the theoretical value. As observed SEM micrograph of the fracture surfaces of the PMT-PT ceramics system, the average grain sizes were increased about 3-5 ${\mu}m$ to 6-8 ${\mu}m$ with increasing sintering temperature. The specimens with PT<0.30 for PMT-PT solid solution system exhibited the dielectric and pyroelectric properties of a typical relaxor ferroelectrics. The composition with the maximum dielectric constant exhibits relatively superior pyroelectric and piezoelectric properties.

Dielectric and Ferroelectric Properties of Nb Doped BNT-Based Relaxor Ferroelectrics

  • Maqbool, Adnan;Hussain, Ali;Malik, Rizwan Ahmed;Zaman, Arif;Song, Tae Kwon;Kim, Won-Jeong;Kim, Myong-Ho
    • Korean Journal of Materials Research
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    • v.25 no.7
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    • pp.317-321
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    • 2015
  • The effects of Nb doping on the crystal structure, microstructure, and dielectric ferroelectric and piezoelectric properties of $(Bi_{0.5}Na_{0.5})_{0.935}Ba_{0.065}Ti_{(1-x)}Nb_xO_3-0.01SrZrO_3$ (BNBTNb-SZ, with ${\chi}=0$, 0.01 and 0.02) ceramics have been investigated. X-ray diffraction patterns revealed that all ceramics have a pure perovskite structure with tetragonal symmetry. The grain size of the ceramics slightly decreased and a change in grain morphology from square to spherical shape was observed in the Nb-doped samples. The maximum dielectric constant temperature ($T_m$) increases with increasing amount of Nb; however, ferroelectric-relaxor transition temperature ($T_{F-R}$) and maximum dielectric constant (${\varepsilon}_m$) values decrease gradually. Nb addition disrupted the polarization hysteresis loops of the BNBT-SZ ceramics by leading a reduction in the remnant polarization coercive field and piezoelectric constant.

Preparation and Field-Induced Electrical Properties of Perovskite Relaxor Ferroelectrics

  • Fan, Huiqing;Peng, Biaolin;Zhang, Qi
    • Transactions on Electrical and Electronic Materials
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    • v.16 no.1
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    • pp.1-4
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    • 2015
  • (111)-oriented and random oriented $Pb_{0.8}Ba_{0.2}ZrO_3$ (PBZ) perovskite relaxor ferroelectric thin films were fabricated on Pt(111)/$TiO_x$/$SiO_2$/Si substrate by sol-gel method. Nano-scaled antiferroelectric and ferroelectric two-phase coexisted in both (111)-oriented and random oriented PBZ thin film. High dielectric tunability (${\eta}=75%$, E = 560 kV/cm) and figure-of-merit (FOM ~ 236) at room temperature was obtained in (111)-oriented thin film. Meanwhile, giant electrocaloric effect (ECE) (${\Delta}T=45.3K$ and ${\Delta}S=46.9JK^{-1}kg^{-1}$ at $598kVcm^{-1}$) at room temperature (290 K), rather than at its Curie temperature (408 K), was observed in random oriented $Pb_{0.8}Ba_{0.2}ZrO_3$ (PBZ) thin film, which makes it a promising material for the application to cooling systems near room temperature. The giant ECE as well as high dielectric tunability are attributed to the coexistence of AFE and FE phases and field-induced nano-scaled AFE to FE phase transition.

Relaxor Behaviors in xBaTiO3-(1-x)CoFe2O4 Materials

  • Dung, Cao Thi My;Thi, Nhu Hoa Tran;Ta, Kieu Hanh Thi;Tran, Vinh Cao;Nguyen, Bao Thu Le;Le, Van Hieu;Do, Phuong Anh;Dang, Anh Tuan;Ju, Heongkyu;Phan, Bach Thang
    • Journal of Magnetics
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    • v.20 no.4
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    • pp.353-359
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    • 2015
  • Dielectric properties of $xBaTiO_3-(1-x)CoFe_2O_4$ composite materials have been investigated. Dielectric properties of $BaTiO_3$, $CoFe_2O_4$ and $0.5BaTiO_3-0.5CoFe_2O_4$ samples show frequency dependence, which is classified as relaxor behavior with different relaxing degree. The relaxor behaviors were described using the modified Curier-Weiss and Vogel-Fulcher laws. Among three above samples, the $BaTiO_3$ sample has highest relaxing degree. Photoluminescence spectral indicated defects, which might in turn control relaxing degree.