Abstract
The temperature dependence of the resistivity and Seebeck coefficient for the two p-type systems , 0≤δ≤0.09, and , 0≤x≤0.3, are reported and interpreted in the context of overall phase diagrams. Above room temperature, the system tends to lose oxygen at 1 atm ; superconductive samples exhibit a first-order loss of oxygen above 500 K to revert to the antiferromagnetic phase. Below a transition temperature ≊300 K, compositions with 0<δ<0.05 undergo phase segregation to an antiferromagnetic and a superconductive phase; the superconductive phase appears to undergo a further dynamic segregation into hole-rich and hole-poor domains in the interval <T<≊100 K. In the system , the holes move diffusively, with a Δ=0, above ≊300 K for the compositions 0<x≤0.21; the system undergoes a transition from a p-type two-dimensional conductor to an n-type three-dimensional conductor in the interval 0.22≤x<0.35.
Compositions with 0<x≤0.12 are metastable in the range <T< where the holes continue to move diffusively, but charge fluctuations appear in the range <T<≤150 K. Compositions with 0.15≤x≤0.2 appear to undergo a transition from a polaronic gas to a polaronic (Luttinger) liquid on cooling through ; superconductive pairs are condensed from the homogeneous polaronic-liquid normal state at . The origin of the unusual electron-lattice interactions in the normal state of the superconductive compositions is attributed to a coexistence of ionic and covalent bonding at a transition from more ionic to covalent Cu:3--O:2 bonding in the sheets; through the transition the orbital hybridization and Hubbard U parameter vary sensitively with both the Cu-O bond length and the formal local oxidation state at a Cu atom.
- Received 29 September 1992
DOI:https://doi.org/10.1103/PhysRevB.47.5275
©1993 American Physical Society