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Bulk Wave Characterization of High TC Superconductors

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Annual summary rept. 1 Aug-1 Nov 1988

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The objective of this research is to characterize high TC superconductors with longitudinal and transverse ultrasonic waves. Both attenuation and velocity measurements have been performed on sinter forged samples of YBa2Cu3O7, which has two CuO planes perpendicular to the c-axis per unit cell. Three elastic constants, C11, C33 and C44, out of five , for this axially symmetric sample, with 80 percent of the c-axis of platelet like crystallites aligned along the forging axis, have been determined. Three maxima in attenuation are observed at 70 K, 180 K, and 250 K when longitudinal waves are propagated perpendicular to the forging axis. Only the middle maximum is observed when either longitudinal or transverse waves propagate parallel to the forging axis or perpendicular to CuO planes. Thus, the middle maximum may be due to an isotropic interaction while the other maxima may be produced by interactions associated with distortions of the CuO planes. Frequency dependent measurements on sintered samples of YBa2Cu3O7 show that the low temperature maximum is produced by a relaxation mechanism. The activation energy of the relaxation time for this maximum is about 400 k which is near the Debye temperature of this compound. Sound measurements in a sample of Ba0.625K0. 375BiO3, which has a Tc28 k and which is postulated to be a BCS superconductor, show a maximum in attenuation around 50 K. Yttrium compound, Barium compounds, Copper oxides.

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  • Inorganic Chemistry
  • Electricity and Magnetism

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