Synthesis of (M0.33Cu0.67) Sr(2)YCu(2)Oy: a novel layered cuprate with a block layer of (As0.33Cu0.67) O-0.88

Conditions for forming a single phase of (M0.33Cu0.67)Sr2YCu2Oy [(M, Cu)-12 12] were examined. When the valence of M ions ranged from divalent to hepta valent, the (M, Cu)-1212 phase was formed. A wide tolerance of the M valenc e in (M0.33Cu0.67)Sr2YCu2Oy is originated from the oxygen vacancy in the (M 0.33Cu0.67)O-z layer. On the other hand, the ionic radius of M was closely correlated with the formation of (M, Cu)-1212, showing that the ionic radiu s of the M ion is an important factor in the preparation of the 1212 phase. Among these compounds, (As0.33Cu0.67)Sr2YCu2Oy was newly prepared. The (As 0.33Cu0.67)Sr2YCu2O6.88 has a tetragonal unit cell with a = 3.830 Angstrom and c = 11.47 Angstrom. Annealing the sample in an oxygen atmosphere led to an increase in the Cu valence as large as 2.38. However, resistivity measu rement showed that (As0.33Cu0.67)Sr2YCu2O6.88 was not superconducting but s emiconducting. Nonsuperconductivity of (As0.33Cu0.67)Sr2YCu2O6.88 was attri buted to the fact that the large number of O ions were located in O(3) site , which resulted in localization of holes. In this case, about 50% of oxyge n ions in the (As, Cu)O-0.88 layer is located at O(3) site, leading to loca lization of holes. If the number of oxygen ions in the O(4) site is increas ed, superconductivity can be expected. (C) 2000 Elsevier Science B.V. All r ights reserved.