Superconductivity Research Laboratory, ISTEC, 1-10-13 Shinonome, Koto-ku, Tokyo 135, Japan
Abstract:
The polarized Raman spectra of Nd1+xBa2?xCu3O7?δ (?0.023≤x≤0.107) and Pr1+xBa2?xCu3O7?δ (0.01≤x≤0.15) single crystals have been investigated. It was found that the Cu(2) Ag mode softens by 6 cm?1 in Nd 1:2:3 and 4 cm?1 in Pr 1:2:3 as x increases. These frequency shifts cannot be explained by the change in the relevant bond lengths due to Nd(Pr)-substitution for Ba. The variations with x of the two low frequency modes may be affected by change of their hybridization and/or change of their force constants. The linewidths of Ba mode in Pr 1:2:3 are broader than those in Y 1:2:3. This result suggests that the Pr substitution on Ba sites occurred even in a very small value of x. In x(yy) geometry the relative intensity of the Ba and O(4) modes in Nd 1:2:3 is greater than those in Pr 1:2:3. The difference between Nd 1:2:3 and Pr 1:2:3 in the relative intensity of the Ba and O(4) modes may be produced by the chains.