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Ultrasonic Characterization of High Tc and other Unconventional Superconductors.

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Final rept. 1 Jan 91-30 Jun 97,

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Ultrasonic techniques were used to characterize the properties of high Tc and other unconventional superconductors. A pontoon technique was developed to investigate thin films with surface acoustic waves SAW. A cw sampling technique was modified in order to sensitively study vortex motion in small superconducting single crystals of YBCO. The penetration field of melt textured YBCO was observed ultrasonically and analysis of the data yields the superconducting energy gap in its domain boundaries. Phase diagrams of superconducting UPt3 were determined ultrasonically. The effect of a coherence phase transition on ultrasonic attenuation in CeCu6 was measured. A theoretical model was developed to quantitatively explain the decrease in insertion loss at the superconducting transition of a SAW delay line made with YBCO interdigital electrodes. Two sets of attenuation and velocity signatures were observed in a large single crystal La1.85Sr0.15CuO4 which correspond to the superconducting transition and to a Neel transition in the superconducting state. SAW measurements using the pontoon technique on single crystals and thin films of YBCO demonstrate the importance of pinning sites in determining the nature of vortex transitions. A two dimensional theoretical model was developed for determining the acoustic radiation impedance of resonating rectangular parallelepipeds. The effect of a surrounding medium on the resonance spectra of a vibrating solid sphere was derived theoretically, and the theoretical results compare favorably with experimental data.

Subject Categories:

  • Inorganic Chemistry
  • Line, Surface and Bulk Acoustic Wave Devices
  • Electricity and Magnetism
  • Crystallography

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