Oxygen isotope effect and structural phase transitions in La2CuO4-based superconductors

• Published in: Science (American Association for the Advancement of Science) Vol. 250; no. 4986; pp. 1390 - 1394
• Main Authors: CRAWFORD, M. K, FARNETH, W. E, MCCARRON, E. M, HARLOW, R. L, MOUDDEN, A. H
• Format: Journal Article
• Language: English
• Published: Washington, DC American Association for the Advancement of Science 07.12.1990
• Subjects: Condensed matter: structure, mechanical and thermal properties; Copper oxide superconductors; Exact sciences and technology; High temperature superconductivity; Inorganic compounds; Isotopes; Oxygen; Oxygen isotopes; Physics; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Transiens phase; Superconducting materials; Oxygen; Temperature; Radioisotope; Structure
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.250.4986.1390

The oxygen isotope effect on the superconducting transition temperature (alpha(o)) varies as a function of x in La2-xSrxCuO(4) and La2-xBaxCuO(4), with the maximum alpha(o) values (alpha(o) >/= 0.5) found for x near 0.12. This unusual x dependence implies that the isotope effect is influenced by proximity to the Abma --> P4(2)/ncm structural phase transition in these systems. Synchrotron x-ray difaction measurements reveal little change in lattice parameters or orthorhombicity due to isotope exchange in strontium-doped materials where alpha(o) > 0.5, eliminating static structural distortion as a cause of the large isotope effects. The anomalous behavior of alpha(o) in both strontium- and barium-doped materials, in combination with the previously discovered Abma --> P4(2)/ncm structural phase-transition in La(1.88)B(0.12)CuO(4), suggests that an electronic contribution to the lattice instability is present and maximizes at approximately 1/8 hole per copper atom. These observations indicate a dose connection between hole doping of the Cu-O sheets, tilting instabilities of the CuO(6) octahedra, and superconductivity in La(2)CuO(4)-based superconductors.