  In this work we present the study of the elastic properties of
polycrystalline samples of superconducting YBa_2Cu_3O_7 prepared by the sol-gel
method. The quality of all samples was checked by x-ray diffraction and
scanning electronic microscopy while their physical properties were verified by
transport and magnetic measurements. The elastic study was performed using the
standard pulse-echo technique through measuring the phase velocity and the
attenuation of ultrasonic waves (in the range of a few MHz) as a function of
temperature. We have focused this study on the low temperatures interval (T <
200K). The obtained results show a strong hysteretic behavior in the ultrasonic
attenuation (in addition to usually observed hysteretic behavior for the
velocity) which strongly supports the existence of a martensitic-like phase
above the superconducting critical temperature T_C. We argue that this peculiar
behavior can be attributed to the granularity present in the samples.
