500-600 K dilatation anomaly and T_c increase in YBa₂Cu₃O_x

YBa₂Cu₃O_x bulk ceramics have been simultaneously investigated by the thermal expansion and the acoustic emission methods in the 500-600 K temperature range. An error of the differential dilatometer does not exceed 10^-7. At T = 555 K, the dilatation anomaly accompanied by the acoustic emission has been observed and measured. Based on this measured anomaly, a value of Δc = -0.003 μm has been determined. And based on this Ac size the stoichiometric coefficient x = 7.01 has been calculated too. The possible mechanism for T_c increase in YBa₂Cu₃O_x as a result of closing b axis by the absorbed oxygen atoms during the samples' heating through 500-600 K has been discussed.