Abstract
Synchrotron x-ray and neutron-diffraction measurements demonstrate that substitution at the site in both metallic and insulating induces low-temperature structural instabilities which reorient the tilting of the copper-oxygen octahedra. These structural transformations strongly affect superconductivity. In addition, there is a bicritical point involving phases of Bmab, Pccn, and P/ncm space-group symmetries in the structural phase diagram of at x∼0.15. There are also anomalies in the structural transformation temperatures and the superconducting transition temperatures when x∼1/8, providing evidence for an electronic instability at this doping level.
- Received 2 May 1991
DOI:https://doi.org/10.1103/PhysRevB.44.7749
©1991 American Physical Society