Structural studies of La/sub 2-x/Ba/sub x/CuO/sub 4/ between 11-293 K

Technical Report · Fri Jan 01 04:00:00 EST 1988

DOI:https://doi.org/10.2172/5973654· OSTI ID:5973654

Cox, D. E.; Zolliker, P.; Axe, J. D.; Moudden, A. H.; Moodenbaugh, A. R.; Xu, Y.

Neutron powder diffraction data have been collected from samples of La/sub 1.9/Ba/sub 0.1/CuO/sub 4/ and La/sub 1.85/Ba/sub 0.1515/CuO/sub 4/ in the temperature range 11-293K. The first material undergoes a phase transition from the tetragonal K/sub 2/NiF/sub 4/-type structure (space group I4/mmm) to the orthorhombic La/sub 2/CuO/sub 4/-type structure (space group Bmab) at about 280K, and then a second transition to another type of tetragonal (or near-tetragonal) structure with probable space group P4/sub 2//ncm. The latter transition occurs predominantly between 50-40K, but about 10% of the orthorhombic phase persists down to 15K. Rietveld refinement was carried out at selected temperatures in the different structural regions. The differences among the low temperature structures can be characterized by tilting of the CuO/sub 6/ octahedra about different rotation axes on the basis of the simple X-Y model previously proposed by Axe and coworkers. The tilt angle, which is a measure of the long-range order parameter, is about 3.5/degree/ at 15K. Data sets were also collected from La/sub 1.85/Ba/sub 0.15/CuO/sub 4/ at 293, 90 and 11K. At the two latter temperatures there was some peak broadening consistent with the distortions observed in previous high resolution neutron (Paul and co-workers) and x-ray (Axe and co-workers) powder studies. Rietveld analysis of the data indicated the presence of local octahedral displacements, but it was not possible to determine the nature of the correlations. 20 refs., 5 figs., 3 tabs.

• Research Organization: Brookhaven National Lab., Upton, NY (USA)
• DOE Contract Number: AC02-76CH00016
• OSTI ID: 5973654
• Report Number(s): BNL-42865; ON: DE89015104
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360202* -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
ALKALINE EARTH METAL COMPOUNDS
BARIUM COMPOUNDS
BARIUM OXIDES
CHALCOGENIDES
COHERENT SCATTERING
COPPER COMPOUNDS
COPPER OXIDES
CRYSTAL LATTICES
CRYSTAL STRUCTURE
DIFFRACTION
LANTHANUM COMPOUNDS
LANTHANUM OXIDES
NEUTRON DIFFRACTION
ORTHORHOMBIC LATTICES
OXIDES
OXYGEN COMPOUNDS
RARE EARTH COMPOUNDS
SCATTERING
SUPERCONDUCTORS
SUPERLATTICES
TETRAGONAL LATTICES
TRANSITION ELEMENT COMPOUNDS