Experimental confirmation of the isotopic volume effect in superconducting molybdenum by means of energy-dispersive x-ray diffration at low temperatures |
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Authors: | T. Nakajima T. Fukamachi O. Terasaki S. Hosoya |
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Affiliation: | (1) The Research Institute for Iron, Steel and Other Metals, Tohoku University, Sendai, Japan;(2) Institute for Solid State Physics, University of Tokyo, Minato-ku, Tokyo, Japan;(3) Faculty of Science, Tohoku University, Sendai, Japan;(4) Institute for Solid State Physics, University of Tokyo, Minato-ku, Tokyo, Japan |
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Abstract: | Differences in the lattice constants of Mo-100 and Mo-92 have been measured by x-ray diffraction, in order to search directly for the volume effect of isotopes in a superconductor. No significant difference in the lattice constanta(Mo-100)–a(Mo-92) could be detected at 290 K, while the differences –0.0014±0.0008 and –0.0029±0.0009 Å were detected at 85.3 and 4.31 K, respectively. These values, and their temperature dependence, are considered to be theoretically reasonable. The exponent in the isotope effect defined by TcM- is represented thermodynamically by =–( lnTc/ lnM)–( lnTc/ lnV)(d lnV/d lnM). From the results, d lnV/d lnM is found to be –0.033±0.009 at 4.31 K. Then, the second term representing the isotopic volume effect is estimated to be about 0.09, with lnTc/ lnV2.81. The observed value of is 0.33, so that the contribution of the second term, 0.09, is 27% of the value of . It becomes quite clear that the isotopic volume effect in superconducting Mo should not be neglected. |
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