Synthesis of (M 0.33Cu 0.67)Sr 2YCu 2O y: a novel layered cuprate with a block layer of (As 0.33Cu 0.67)O 0.88

Abstract

Conditions for forming a single phase of (M 0.33Cu 0.67)Sr 2YCu 2O y [(M, Cu)-1212] were examined. When the valence of M ions ranged from divalent to heptavalent, the (M, Cu)-1212 phase was formed. A wide tolerance of the M valence in (M 0.33Cu 0.67)Sr 2YCu 2O y is originated from the oxygen vacancy in the (M 0.33Cu 0.67)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 radius of the M ion is an important factor in the preparation of the 1212 phase. Among these compounds, (As 0.33Cu 0.67)Sr 2YCu 2O y was newly prepared. The (As 0.33Cu 0.67)Sr 2YCu 2O 6.88 has a tetragonal unit cell with a=3.830 Å and c=11.47 Å. Annealing the sample in an oxygen atmosphere led to an increase in the Cu valence as large as 2.38. However, resistivity measurement showed that (As 0.33Cu 0.67)Sr 2YCu 2O 6.88 was not superconducting but semiconducting. Nonsuperconductivity of (As 0.33Cu 0.67)Sr 2YCu 2O 6.88 was attributed 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 oxygen ions in the (As, Cu)O 0.88 layer is located at O(3) site, leading to localization of holes. If the number of oxygen ions in the O(4) site is increased, superconductivity can be expected.