Ultrasonic studies in YBa2Cu3O7 and gallium-doped YBa2Cu3O7

The temperature dependence of the ultrasonic velocity and attenuation was measured in pure YBa₂Cu₃O₇ and in samples doped with Ga. Doping concentrations between 2 and 7 at.% were used. Both longitudinal waves and shear waves were studied for frequencies between 5 and 50 MHz. The results show that the low-temperature peak in the attenuation and the anomalous hardening which usually occurs near T_c in pure samples is not present in doped samples and therefore suggests that these features are not associated with the superconducting transition temperature. The results are compared with those of other ultrasonic studies and recent internal friction studies