Radio-frequency acoustic powder echoes in high-T-c Bi2Sr2CaCu2O8 around the H-T phase boundary

Temperature dependence of intensity of rf acoustic powder echoes is studied for powdered samples of Bi2Sr2CaCu2O8 ceramics around the H-T phase boundary and compared with combined magnetization data in field-cooled and zero-field cooled conditions for the same powder. Rf acoustic powder echoes are found to vanish at H-C2 rather than H-irr determined from the magnetization data and we conclude that the intrinsic pinning is important for the observation of rf acoustic powder echoes in the high-T-c Bi(2)sr(2)CaCu(2)O(8) ceramics, Hysteretic behavior observed around H-C2, suggests an existence of the first-order phase transition at the H-C2 line.