Neutron and synchrotron x-ray powder-diffraction study of La sub 2 CuO sub 4+. delta
- Physics Department, Brookhaven National Laboratory, Upton, NY (USA)
- Mineral Physics Institute, State University of New York, Stony Brook, NY (USA) Department of Earth and Space Sciences, State University of New York, Stony Brook, Stony Brook, NY (USA)
- E.I. DuPont de Nemours Co., Wilmington, DE (USA)
A detailed synchrotron x-ray and neutron powder-diffraction study has been carried out in the temperature range 10--500 K on an oxygen-rich superconducting ({Tc}{approx}35 K) sample of La{sub 2}CuO{sub 4+{delta}} prepared under an oxygen pressure of 3 kbar. The value of {delta} was determined to be 0.03{plus minus}0.01 by a combination of thermogravimetric and mass-spectrometric techniques. Two phase transitions were found, generally similar to those reported in a recent neutron-diffraction study of this system by Jorgensen {ital et} {ital al}. (Phys. Rev. B 38, 11 337 (1988)). At 297 K, the sample was single phase with orthorhombic symmetry (space group {ital Bmab}, {ital a}=5.357 A, {ital b}=5.389 A, {ital c}=13.175 A), but with a significant amount of anisotropic broadening of the x-ray-diffraction peaks. Upon cooling a reversible phase transformation was found to set in at 290 K, characterized by the appearance of a second orthorhombic phase in coexistence with the first, with slightly different {ital b} and {ital c}, but identical {ital a}, unit-cell dimensions. Between 290 and 250 K, the amount of second phase increased steadily until the two phases were present in roughly equal proportions. No further change was observed down to 10 K. At the latter temperature, the symmetries of the two phases were consistent with space groups {ital Bmab} and {ital Fmmm}, respectively, as reported by Jorgensen {ital et} {ital al}.; surprisingly, however, it is the {ital Bmab} phase that evolves below 290 K, as shown by the temperature dependence of the unit-cell parameters. Upon heating above 297 K, there was a phase transformation from orthorhombic to tetragonal symmetry (space group {ital I}4/{ital mmm}) at about 410 K. No discontinuity in the temperature dependence of the {ital a} dimension could be detected between 10 and 410 K.
- DOE Contract Number:
- AC02-76CH00016
- OSTI ID:
- 6259448
- Journal Information:
- Physical Review, B: Condensed Matter; (USA), Journal Name: Physical Review, B: Condensed Matter; (USA) Vol. 42:10; ISSN 0163-1829; ISSN PRBMD
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360202* -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
BREMSSTRAHLUNG
COHERENT SCATTERING
COPPER COMPOUNDS
CUPRATES
DIFFRACTION
ELECTROMAGNETIC RADIATION
HIGH TEMPERATURE
HIGH-TC SUPERCONDUCTORS
LANTHANUM COMPOUNDS
LOW TEMPERATURE
MEDIUM TEMPERATURE
NEUTRON DIFFRACTION
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
RADIATIONS
RARE EARTH COMPOUNDS
SCATTERING
SUPERCONDUCTORS
SYNCHROTRON RADIATION
TRANSITION ELEMENT COMPOUNDS
ULTRALOW TEMPERATURE
VERY LOW TEMPERATURE
X-RAY DIFFRACTION