Structural phase transitions in bulk YBa{sub 2}Cu{sub 3}O{sub 6+{ital x}} with {ital x}=0.35 and {ital x}=0.36
Journal Article
·
· Physical Review, B: Condensed Matter
- Hamburger Synchrotronstrahlungslabor, HASYLAB at DESY, Notkestrasse 85, D-22603 Hamburg (Germany)
- Department of Solid State Physics, Riso/ National Laboratory, 4000 Roskilde (Denmark)
- Department of Physics, The University of British Columbia, Vancouver, British Columbia, Canada, V6T 1Z1 (CANADA)
The structural behavior of mm{sup 3}-sized single crystals of YBa{sub 2}Cu{sub 3}O{sub 6+{ital x}} with oxygen concentrations close to the metal-insulator transition is studied as a function of temperature, using 95-keV synchrotron x-ray diffraction. At {ital x}=0.36, no evidence is found of a room-temperature phase separation into tetragonal and orthorhombic phases, nor of a phase boundary between Ortho-II and tetragonal. Instead, we observe two distinct phase transitions: tetragonal to Ortho-I with a critical temperature {ital T}{sub {ital O}I}=246(2){degree}C and Ortho-I to Ortho-II with {ital T}{sub {ital O}II}=85(10){degree}C. Measurements of the spontaneous strain show the {ital O}/{ital T} transition to be nearly continuous with a critical exponent {beta}=0.34(2), consistent with a 3D Ising model driven weakly first order, presumably by the strain. A memory effect is observed, where relics of the twin domains{emdash}possibly related to tweed formations{emdash}continue to exist in the tetragonal phase when the temperature is increased above {ital T}{sub {ital O}I}. Corresponding measurements for {ital x}=0.35 gave similar results{emdash}with {ital T}{sub {ital O}I}=181(2){degree}C, {ital T}{sub {ital O}II}=95(10){degree}C, and {beta}=0.35(2){emdash}but with the appearance of a small tetragonal component at room temperature. This component is interpreted as a nonequilibrium feature. In both cases the Ortho-I to Ortho-II transformations are very broad with a characteristic temperature dependence of the widths of the superstructure peaks that are similar to results obtained in a previous study for {ital x}=0.50. By comparison of the Ortho-II correlation lengths along {ital a}, {ital b}, and {ital c} with the corresponding data for {ital x}=0.50 we find evidence for a strong {ital x} dependency of {ital ASYNNNI}-type effective interaction parameters. (Abstract Truncated)
- OSTI ID:
- 284712
- Journal Information:
- Physical Review, B: Condensed Matter, Journal Name: Physical Review, B: Condensed Matter Journal Issue: 22 Vol. 53; ISSN 0163-1829; ISSN PRBMDO
- Country of Publication:
- United States
- Language:
- English
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