Physica C: Superconductivity and its applications

Raman modes of YBa2Cu3Ox with variable content

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We have measured the Raman spectra of single crystals of YBa2Cu3O7-gd as a function of oxygen concentration, that is Y123-Ox, where x varies from approximately 7 (superconducting) to 6 (insulating). We have made similar measurements on single crystals of Sm123, Gd123, and Ho123. The experimental results from all of these single crystals are very similar. Our single crystal results are in distinct disagreement with experimental results on ceramic of these same materials. For x=7 the usual five, c-axis polarized modes are observed; mode #5 occurs at ∼ 500 cm-1 and is primarily due to motion of oxygen atoms in the four-coordinated Cu chain. At oxygen contents near the metal-insulator (M-I) phase transition, the intensity of mode #5 rapidly decreases and disappears, being replaced by a strongly (zz) polarized mode at ≈ 600 cm-1. We assign the 600 cm-1 mode to oxygen atom vibration in the two-coordinated Cu "sticks". At the oxygen content near the M-I phase transition, other weaker lower-energy modes appear and these are discussed. However, these modes disappear for oxygen content x≈6, where the approxiate number of symmetry allowed modes (five) is again observed. © 1991.


01 Oct 1991


Physica C: Superconductivity and its applications