Enhancement of T_c, Shielding and Irreversibility Line in Argon Preheated Ln(SrBa)Cu₃ ${rm LnSrBaCu}_{3}{rm O}_{6+{rm z}}$ $({rm Ln}={rm rare} {rm earth})$ ceramic cuprites; Chain oxygen order-disorder; heat treatments control of $T_{c}$; irreversibility line; magnetic shielding;

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