J. Feller
C. Hucho
R. Gaffney
M. J. McKenna
B. K. Sarma
M. Levy
Dept. of Phys., Univ. of Wisconsin, Milwaukee, WI 53201
Pulsed surface acoustic waves (SAW's) at 165 MHz are used to study the superconducting transition and an apparent structural phase transition in films of YBa[sub 2]Cu[sub 3]O[sub 7-(delta)] (YBCO). The structural phase transition occurs in the temperature range 200--230 K and is evidenced by large changes in SAW attenuation and velocity. Small changes are also seen at the superconducting transition temperature. These changes are markedly different when a conventional conductor (e.g., copper) is brought into close proximity to the YBCO film. The results of this investigation are in agreement with the hypothesis that YBCO is piezoelectric below the 200 K transition. [This work was supported by the Office of Naval Research, with C. Hucho supported by Deutsche Forschungsgemeinschaft.]