Synthesis and structural characterisation of YSr2Cu3−xMxO7±y (M = Fe, Ti, Al, Co, Ga, Pb; 0.5 < x < 1), and the non-existence of the parent phase YSr2Cu3O7

TLDR: The possibility of synthesizing phases of general composition YSr 2 Cu 3− x M x O 7± y has been examined for a wide variety of metals M.

Abstract: The possibility of synthesising phases of general composition YSr 2 Cu 3− x M x O 7± y has been examined for a wide variety of metals M. Single phase tetragonal products (typically a = 3.83 A , c = 11.5 A ) can be synthesised provided that the concentration of M is sufficiently large ( x > 0.5), and M has a preference for the Cu(1) sites (the four-coordinate sites) of the YBa 2 Cu 3 O 7 , structure. Neutron diffraction has demonstrated that a high degree of disorder exists in the (001) planes containing the M cations and, in particular, significant oxygen displacements are found. The non-existence of the unsubstituted variant YSr 2 Cu 3 O 7 is explained in terms of the high degree of compressive stress on the Cu(1) sites which could exist in such a material.