Raman Spectroscopy of (Pb sub (1+x)/2 Cu sub (1--x)/2 )Sr sub 2 (Y sub 1--x Ca sub x ) Cu sub 2 O sub 7+ delta (x = 0, 0.35)

Polarized Raman spectra of Pb sub (1+x)/2 Cu sub (1--x)/2 Sr sub 2 Y sub 1--x Ca sub x Cu sub 2 O sub 7+ delta (x = 0, 0.35; delta approx = 0, 0.1) microcrystals have been obtained with various scattering configurations, allowing a distinction between Raman modes of different symmetry. Three A sub 1g and the B sub 1g modes, inherent to the ideal I4/mmm structure, have been unambiguously identified. Additional Raman modes, activated due to displacements of oxygen \O(3)\ atoms from the (1c) sites in the Pb--O(3) planes, have been observed. A strong dependence of the frequency vs. O and Ca contents has been observed for the A sub 1g Raman active mode involving mainly vibrations of apex O atoms \O(2)\. The variations of the Raman spectra with x and delta are discussed.