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Acoustic emission (AE) of the HTS ceramic YBa2Cu3O7−δ is studied under heating from liquid nitrogen temperature. For heating at a high rate, a peak in the AE activity is observed in the temperature interval 100–115 K. The parameters of the peak depend on the oxygen content in the HTS ceramic, heating rate, initial temperature to which the ceramic was cooled, and the sample thickness. The observed AE is associated with the relaxation of microscopic thermal stresses generated at the grain boundaries due to anisotropy of the thermal expansion coefficients and their anomalous behavior at these temperatures. Possible relaxation mechanisms of such stresses are the movement of dislocation groups and the formation of microcracks along the least favorably oriented grain boundaries.

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