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Isotope effect on Raman spectra of polycrystalline La 0.67 Ca 0.33 MnO 3
Author(s) -
Zhang P. X.,
Huang S. J.,
Habermeier H. U.,
Zhao G. M.
Publication year - 2001
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.772
Subject(s) - raman spectroscopy , analytical chemistry (journal) , raman scattering , crystallite , chemistry , isotopic shift , phonon , excitation , wavenumber , isotope , blueshift , isotopes of oxygen , nuclear magnetic resonance , kinetic isotope effect , spectral line , materials science , atomic physics , condensed matter physics , crystallography , optics , deuterium , photoluminescence , physics , nuclear chemistry , optoelectronics , chromatography , quantum mechanics , astronomy
Micro‐Raman spectra were recorded for two samples of polycrystalline La 0.67 Ca 0.33 MnO 3 , which were synthesized from oxides with oxygen isotopes 16 O and 18 O. Isotope Raman shifts were measured and compared with the theoretical prediction. In this way the oxygen‐related Raman modes were clearly identified. Temperature‐related blue Raman shifts for 16 O ( 18 O) vibration modes at 230 cm −1 (216 cm −1 ) were unexpectedly observed. These blue Raman shifts were compared with the blue shift due to lattice parameter variation as the temperature is lowered. The large blue Raman shift that occurs with decrease in temperature demonstrates that the Jahn–Teller distortion may play an important role. The appearance of new peaks at 440–480 and 410–450 cm −1 for 16 O and 18 O samples, respectively, as the temperature decreases to 140–100 K indicates a possible charge–orbit ordering transition. A continuous low‐wavenumber signal was observed which is superimposed on the broad phonon Raman lines. It was found that the scattering intensity of the low‐wavenumber signal is dramatically reduced as the temperature is lowered. The nature of this excitation is not clear. Copyright © 2001 John Wiley & Sons, Ltd.