LongPeriod Modulated Structures of Bi_2Sr_2(Ca_<1x>Ln_x)Cu_2O_<8+d> Ceramics Studied by HighResolution Electron Microscopy and Electron Diffraction
Project/Area Number  03650524 
Research Category 
GrantinAid for General Scientific Research (C)

Allocation Type  Singleyear Grants 
Research Field 
Physical properties of metals

Research Institution  TOHOKU UNIVERSITY 
Principal Investigator 
ONOZUKA Takashi Tohoku University, Institute for Materials Research, Assistant, 金属材料研究所, 助手 (10005936)

Project Period (FY) 
1991 – 1992

Project Status 
Completed(Fiscal Year 1992)

Budget Amount *help 
¥2,100,000 (Direct Cost : ¥2,100,000)
Fiscal Year 1992 : ¥600,000 (Direct Cost : ¥600,000)
Fiscal Year 1991 : ¥1,500,000 (Direct Cost : ¥1,500,000)

Keywords  Modulated Structure / HighResolution / Microphotometry / Bi_2Sr_2(Ca_<1x>Ln_x)Cu_2O_<8+d> / FrenkelKontrova Model / Discommensuration / Domain Configuration / Modulation period of Lattice / 高分解能電子顕微鏡 / Bi_2Sr_2(Ca_<1X>Ln_X)Cu_2O_<8+δ> / 高温超伝導酸化物 / Bi_2Sr_2(Ca_<1ーX>L_<nx>)Cu_2O_8+δ / 過剰酸素 / デスコメンスレション / 高分解電子顕微鏡像 / 電子線回折 / マイクロホトメトリ 
Research Abstract 
It is often very difficult to analyze structures of crystals with sinusoidlike modulations of lattice based on diffraction data, because the number of measurable superlattice reflection is not sufficient to determine atomic coordinates in the large unit cell of modulated structure. The structure of the Bi_2Sr_2(Ca_<1x>Ln_x)Cu_2O_<8+delta> (Ln=rare earth metal) substitution system is a member of the family of the modulated structures.The present study aims to resolve the modulated structure of the substitution systems of Ln=Y,Nd,Pr and Tb by means of the analyses of [001] highresolution image and electron diffraction pattern, and then, to show the Lnconcentration dependencies of the modulation period and the substitution effects of the elements to the concentration dependence. The results are summarized as follows. 1.A longperiod modulated structure model was proposed, consisting of ordered alignments of domains with extent b_1=4.5b_0 and b_2=5b_0 or b_3=4b_0. The model shows the co
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nsistency with the intensity distribution of electron diffraction. 2.An analysis was carried out based on photometric density distribution curves of onedimensional contrast modulation of [001] highresolution image and computer simulations of the density distribution curve. The result of analysis has elucidated that the ordered alignment of the domains ( domain configuration ) in the crystal has been determined from the density distribution curve directly. 3.The modulation period decreases with the Lnconcentration. The Pr and Tb elements have a larger substitution effect to the concentration dependence of period than the Y and Nd elements. Taking the 2 valence of Ca and 3 of Y as the standard ones, the Nd and Pr or Tb elements serve as the 3 and 3.23.3 valences in the crystals, respectively. The modulation period prefers to show a stairswise decrease with the Lnconcentration. The study on the details of the stairs is in progress newly. The domain configurations found in density distribution curves are equivalent those of the ground states of the onedimensionally competitive system. Less

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Research Products
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