STRUCTURAL INSTABILITY IN (PB,CU) 1212-SUPERCONDUCTING CUPRATES

Investigations by high resolution neutron diffraction of the temperatu re dependence of lattice and structural parameters of 1212 cuprates in the system (Pb,Cu)-Sr-(Y,Ca)-Cu-O are reported. A very clear anomalou s expansion in both (a) under bar and (c) under bar at about 180K was observed for superconducting compositions only. Similar structural ano malies have been reported in other HTSC materials and this T-1 anomaly appears to be a widespread, or perhaps universal feature associated w ith superconductivity in cuprates. Atomic displacements which occur du ring this anomaly are much more marked for atoms in the CuO planes.