EFFECT OF PRASEODYMIUM SUBSTITUTION IN YBA2CU4O8 (1-2-4)

Pr substituted YBa2Cu4O8 (1:2:4) has been synthesized by a solid-state reaction at 930-degrees-C-950-degrees-C in 200 bar oxygen pressure. P r could be substituted only up to 20% i.e., Y0.8Pr0.2Ba2Cu4O8. T(c) de creased with increasing Pr; however, T(c) could be restored by co-subs titution of Ca along with Pr which was possible up to Pr = 0.2 and Ca = 0.1. XANES indicated the presence of Pr3+ but not Pr4+. In 1:2:4, T( c) depends on the rare-earth ion size, and Pr3+ ions cause only a smal l additional suppression of T(c) below that expected from the size of Pr3+. The large ''Pr effect'' in the suppression of T(c) of 1:2:3 is t hus a special property of the 1:2:3 structure.