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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 21, Number 10
BKCSDE 21(10)
October 20, 2000 

Infrared Spectroscopic Evidences for the Superconductivity of La2CuO4-related Compounds: A Superconductivity Probe
Jung-Chul Park, Seon-Woog Cho, Jong-Hak Jeong, Gi-Ho Jeong
We present the effects of temperature (between 10 K and 298 K) and of hole concentration on the frequency and intensity of characteristic phonons in polycrystalline La₂CuO₄-related compounds using FT-IR spectros-copy. The influences of the concentration of carrier doped on the phonon modes are prominent in the IR spectra of La₂CuO₄-related compounds. For La₂-xSrxCuO₄(χ= 0.00, 0.03, 0.07, 0.10, and 0.15) and electrochemically (or chemically) oxidized La₂CuO₄, the intensities of the transverse oxygen mode around 680cm -¹ which cor-responds mainly to Cu-O(1) stretching vibration in the basal plane of CuO6 octahedron, are decreased and dis-appeared depending on the Sr-substitution rate and the amount of excess oxygen, while the longitudinal oxygen mode around 510 cm -¹ corresponding to the Cu-O(2) stretching in the basal plane of CuO6 octahedron are near-ly invariable. In particular, after two cycles of cooling-heating between 10 K and 298 K for these sample, the phonons around 680 cm -¹ are blue shif 13-15 cm -¹, while the phonons around 510 cm -¹ are nearly constant. The introduction of the charge carrier by doping would give rise to the small contraction of CuO6 oc-tahedron as Cu ³+ requires a smaller site than Cu ²+, which results in the shortening of the Cu-O(1) bond length and Cu-O(2) bond length with the increased La-O(2) bond length. These results in the frequency shift of the characteristic phonons. The IR spectra of La₂Li0.5Cu0.5O₄ which exhibits an insulator behavior despite the Cu³+ of nearly 100%, corroborate our IR interpretations. The mode around 710 cm -¹ corresponding to Cu-O(1) stretching vibration is still strongly remained even at low temperature (10 K). Thus, we conclude that the con-duction electrons formed within CuO₂ planes of La₂CuO₄-related superconductors screen more effectively the transverse oxygen breathing mode around 680 cm-¹ depending on the concentration of the doped charge carrier in La₂CuO₄-related compounds, which might use as a superconductivity probe.
973 - 979
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