“…According to the phase diagram of Y123 suggested by Ceder et al [41], a phase transition from ortho-I phase to the mixed ortho-I and ortho-III phase occurs around 200 K. This may be the reason for the sudden hardening as indicated by a step-like elastic anomaly around the same temperature during cooling. In the present work, because Al 3+ partial substitution in EuBa 2 (Cu 1−x Al x ) 3 O 7−ı (x = 0.06, 0.10) substitutes directly into Cu-O chains instead of CuO 2 planes [36,20], the substitution disturbs oxygen ordering in the chains and subsequently caused disappearance of the anomaly.…”