Oxygen dependence of the crystal structure of HgBa{sub 2}CuO{sub 4+{delta}} and its relation to superconductivity
- Reactor Radiation Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)
- Texas Center for Superconductivity, University of Houston, Houston, Texas 77204 (United States)
Powder neutron-diffraction profile refinement techniques have been used to investigate the oxygen dependence of the crystal structure and its effect on the superconducting phase transition in high-quality samples of the superconductor HgBa{sub 2}CuO{sub 4+{delta}} (0.04{le}{delta}{le}0.23). The system remains tetragonal (space group {ital P}4/{ital mmm}) over the full range of temperature (10--300 K) and oxygen concentration explored. The {ital a}-axis lattice parameter decreases smoothly with increasing {delta}, while the {ital c}-axis lattice parameter exhibits a maximum. The extra oxygen in the material is found to randomly occupy the centered O(3) site (1/2, 1/2, 0) in the Hg layer, and no other additional site for the extra oxygen was found in the structure. There is also no mixing of the cations on the Cu and Hg sites. {ital T}{sub {ital c}} is observed to vary strongly with {delta}, increasing from 0 K for {delta}=0.04 to a maximum {ital T}{sub {ital c}}=95 K at {delta}{congruent}0.18, and then decreasing rapidly for larger {delta}. The relationship of {ital T}{sub {ital c}}({delta}) to the rate of hole doping on the CuO{sub 2} planes indicates that this doping level is only half of that expected for O{sup 2{minus}} ions. Our structural studies reveal an interesting correlation between the occupation of the O(3) site and the movement of the Ba ions towards the O(3) and away from the Cu-O planes. The Ba layer thus becomes structurally disordered, and this disorder is found to closely mirror the {ital T}{sub {ital c}}({delta}) behavior. Valence and/or distance arguments for the O(3) then suggest that this oxygen is only singly ionized.
- OSTI ID:
- 76419
- Journal Information:
- Physical Review, B: Condensed Matter, Vol. 52, Issue 1; Other Information: PBD: 1 Jul 1995
- Country of Publication:
- United States
- Language:
- English
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