1988 Fiscal Year Final Research Report Summary
Low-Temperature Electron Microscopy on the Cubic-Tetragonal Transformation of V_3Si and Nb_3Sn
| Project/Area Number |
62550469
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
Physical properties of metals
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| Research Institution | TOHOKU UNIVERSITY |
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Principal Investigator |
ONOZUKA Takashi Associate assistant, Institute for Materials Research, Tohoku Univ., 金属材料研究所, 助手 (10005936)
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| Co-Investigator(Kenkyū-buntansha) |
KAJITANI Tsuyoshi Associate assistant, Institute for Materials Research, Tohoku Univ., 金属材料研究所, 助手 (80134039)
HIRABAYASHI Makoto Professor, Institute for Materials Research, Tohoku Univ., 金属材料研究所, 教授 (00005836)
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| Project Period (FY) |
1987 – 1988
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| Keywords | A15 compounds / High-Tc superconducting ceramic / Phase Transformation / Precursor / 低温電子顕微鏡観察 |
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| Research Abstract |
Structural phase transformations of V_3Si and La_<2-x>Sr_xCuO_4(0.11<greater than or equal>x<greater than or equal>0.18) have been investigated in the temperature range from 8K to room temperature using a 1 MV electron microscope with a double-tilt goniometer cooled by liquid helium and a 200kV electron microscope with a side-entry stage cooled by liquid nitrogen.
The cubic-tetragonal trnasformation of V_3Si takes place at a temperature tm<similar or equal>19K. A remarkable softening of the shear modulus occurs with decreasing temperature down to near Tm, and is ascribed to a precursor of the cubic-tetragonal^- transformation. Below the transformation temperature, fine twin lamellae appear parallel to {110} plane traces, being connected continuously with mottled striations having the same orientation. Fine striations along {110} traces or socalled tweeds are observed below 50K at the precursor of the structural phase transformation. The image contrast of mottled striations and tweed pat
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terns is attributed to the presence of lattice distortion owing to the softening of the shear modulus. Reversible changes of the patterns recorded with a TV-VTR system during cooling and heating process are discussed briefly.
The doped oxides La_<2-x>Sr_xCuO_4 are a family of high-Tc superconducting ceramics, having the superconducting temperature Tc=38K at x=0.15. Those materials undergo a tetragonal-orthorhombic phase transformation which is suppressed by Sr-doping. The occurrence of another phase transformation which is suppressed by Sr-doping. The occurrence of another phase transformation has been suggested by single crystal X-ray studies of La_<1.85>Sr_<0.15>CuO_4. In La_<1.85>Sr_<0.15>CuO_4, twin lamellae associated with the tetragonal-orthorhomblc phase transformation appear quite continuously on cooling in the temperature range of 120K-160K. Its reverse process is observed on heating. Observations of x=0.11, 0.15 and 0.18 down to 8K did not detect any phase transformation in the orthorhombic phase. A tentative phase diagram of La_<2-x>Sr_xCuO_4 is proposed. Less
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Research Products
(6 results)
