Phonon anomalies and structural stability in the R sub 2 minus x Ce sub x CuO sub 4 system ( R =Gd,Sm,Nd,Pr)

Journal Article · Fri Feb 01 00:00:00 EST 1991 · Physical Review, B: Condensed Matter; (USA)

DOI:https://doi.org/10.1103/PhysRevB.43.2857· OSTI ID:5885800

Heyen, E T; Liu, R; Cardona, M ^[1]; Pinol, S; Melville, R J; Paul, D M ^[2]; Moran, E; Alario-Franco, M A ^[3]

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1. Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, D-7000 Stuttgart 80, Federal Republic of Germany (DE)
2. Department of Physics, University of Warwick, Coventry (Great Britain)
3. Departamento de Quimica Inorganica, Facultad de Ciencias Quimicas, Universidad Complutense, 28040 Madrid, (Spain)

We present a comprehensive analysis of Raman spectra in the {ital R}{sub 2{minus}{ital x}}Ce{sub {ital x}}CuO{sub 4} system ({ital R}=Gd,Sm,Nd,Pr) as a function of doping, temperature, rare-earth atomic radius, and Raman resonance conditions. Phonon frequencies as well as their temperature dependences behave anomalously for {ital R}=Pr: The {ital B}{sub 1{ital g}} phonon, for instance, softens by as much as 11 cm{sup {minus}1} when the crystal is cooled from room temperature to 10 K, while it hardens by 11 cm{sup {minus}1} for {ital R}=Nd. These observations are attributed to the fact that Pr, as the largest rare-earth atom that can give rise to the {ital T}{prime} structure, is already close to the {ital T}{prime} stability limit, yielding large phonon anharmonicities in this compound. The dependence of the phonon frequencies on doping is strong only for the oxygen {ital E}{sub {ital g}} mode, which can thus be used for sample characterization. We also present and discuss phonon resonance profiles for Nd{sub 1.85}Ce{sub 0.15}CuO{sub 4} and Nd{sub 2}CuO{sub 4}, which yield electronic structural information that should be compared with future calculations of the resonance profiles. Finally, we also discuss the origin of an additional large {ital A}{sub 1{ital g}}-symmetry peak that shows a dramatic, rare-earth-dependent resonance behavior and gives a possible explanation on the grounds of a partial {ital T}{prime}{r arrow}{ital T} transition. We always observe several well-defined, unexpected vibrational peaks that seem to be intrinsic to the {ital R}{sub 2{minus}{ital x}}Ce{sub {ital x}}CuO{sub 4} system, indicating crystal distortions that have not been conclusively identified by x-ray- or neutron-diffraction experiments so far.

• OSTI ID: 5885800
• Journal Information: Physical Review, B: Condensed Matter; (USA), Vol. 43:4; ISSN 0163-1829
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CERIUM OXIDES
PHONONS
COPPER OXIDES
GADOLINIUM OXIDES
HIGH-TC SUPERCONDUCTORS
NEODYMIUM OXIDES
PRASEODYMIUM OXIDES
SAMARIUM OXIDES
CRYSTAL STRUCTURE
RAMAN SPECTRA
CERIUM COMPOUNDS
CHALCOGENIDES
COPPER COMPOUNDS
GADOLINIUM COMPOUNDS
NEODYMIUM COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PRASEODYMIUM COMPOUNDS
QUASI PARTICLES
RARE EARTH COMPOUNDS
SAMARIUM COMPOUNDS
SPECTRA
SUPERCONDUCTORS
TRANSITION ELEMENT COMPOUNDS
360204* - Ceramics
Cermets
& Refractories- Physical Properties