Lithium-induced moments in tetragonal YBCO

The magnetic susceptibility of various YBa2Cu3-xLixO6+epsilon samples with 0 < x < 0.4 was measured in a held of 1 T in the 4.5-300 K temperature rang e. All the samples were tetragonal and single phase. Considering only the c ell parameter variation does not allow us to conclude what site is occupied by lithium with certainty, the chain site being the most probable because a contraction of the c-axis is observed. As the lithium concentration incre ases, one observes the disappearance of the three-dimensional (3D) antiferr omagnetism in favour of a paramagnetic system revealing the formation of di sordered localised magnetic moments. The observed Curie-type behaviour show s that the substitution of one lithium for one copper ion induces an effect ive moment of (1.13 +/- 0.07) mu(B)/Li, independent of the lithium concentr ation as long as the oxygen content remains equal to (6.03 +/- 0.05). This effective moment is identical to the one induced by lithium in the orthorho mbic YBCOLix materials which leads to the conclusion that lithium occupies the same site in both systems. In pure YBCO6+epsilon, an excess of one oxyg en ion in the chains is found to give rise to one Bohr magneton. (C) 1999 E lsevier Science Ltd. All rights reserved.