Mechanical losses spectroscopy of two superconducting Y1Ba2Cu3O7-x sam
ples (T-c = 93 K) measured at 5, 10, 20 and 30 MHz revealed four peaks
. As the frequency of measurement was increased, the peaks shifted to
higher temperatures. The relaxation process was found to have an activ
ation enthalpy of 0.188, 0.092, 0.209 and 0.314 eV with an attempt fre
quency, f(o), equal to 2.46 x 10(15), 5.95 x 10(10), 1.64 x 10(14), an
d 7.82 x 10(13) Hz for P-1, P-2, P-3 and P-4 peaks, respectively. The
mechanism responsible for these relaxation peaks is discussed. The inf
rared spectra of some of these compounds provide evidence for oxygen r
earrangement on going from tetragonal to orthorhombic phase. X-ray dif
fraction analysis shows that these compounds correspond to a single ph
ase which is an orthorhombic perovskite structure.