AC suscptibility study of YBCO sintered samples near the transition temperature

Y1Ba2Cu307_x sintered samples have been investigated near the transition
temperature by means of AC susceptibility technique. In particular, the intragranular
contribution to the imaginary part of susceptibility (Z") has been studied as a function
of the field frequency (f = 17 Hz + 1070 Hz) in a narrow temperature range (few
degrees) around T c (= 92.0 K). Different frequency dependences of Z" have been
found as the temperature varies. For temperatures T<91.9 K Z" is found to increase
linearly with In f, whereas for T~_ 91.9 K a linear frequency dependence is found.
Moreover, for T<92.3K the zero frequency limit approaches to a finite value, whereas
for T>92.3K such limit is zero.