Phonon anomalies and structural stability in the R sub 2 minus x Ce sub x CuO sub 4 system ( R =Gd,Sm,Nd,Pr)
- Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, D-7000 Stuttgart 80, Federal Republic of Germany (DE)
- Department of Physics, University of Warwick, Coventry (Great Britain)
- 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), Journal Name: Physical Review, B: Condensed Matter; (USA) Vol. 43:4; ISSN PRBMD; ISSN 0163-1829
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360204* -- Ceramics
Cermets
& Refractories-- Physical Properties
CERIUM COMPOUNDS
CERIUM OXIDES
CHALCOGENIDES
COPPER COMPOUNDS
COPPER OXIDES
CRYSTAL STRUCTURE
GADOLINIUM COMPOUNDS
GADOLINIUM OXIDES
HIGH-TC SUPERCONDUCTORS
NEODYMIUM COMPOUNDS
NEODYMIUM OXIDES
OXIDES
OXYGEN COMPOUNDS
PHONONS
PRASEODYMIUM COMPOUNDS
PRASEODYMIUM OXIDES
QUASI PARTICLES
RAMAN SPECTRA
RARE EARTH COMPOUNDS
SAMARIUM COMPOUNDS
SAMARIUM OXIDES
SPECTRA
SUPERCONDUCTORS
TRANSITION ELEMENT COMPOUNDS