Raman spectroscopic study of the La(0.5)R(0.5)Ba(2)Cu(3)O(y) (R=Y, rare earth) superconductors

Two series of materials La(0.5)R(0.5)Ba(2)Cu(3)O(y) (fully oxygenated and deoxygenated, R = Pr, Nd, Sm, Eu, Gd, Dy, Y, Ho, Er, Tm, Yb, Lu) have been prepared with a variation of the solid state reaction technique. X-ray diffraction and Raman measurements have been carried out to study the effect of La substitution for another rare earth. The cell parameters show the usual lanthanide contraction behavior. In the micro-Raman spectra a slight increase of the A(g) mode frequency of the apex oxygen with increasing average La-R ionic radius is observed, while the mode frequencies corresponding to the Ba, Cu(2) (cuprate plane Cu), and the in-phase vibrations of the O(2, 3) (cuprate-plane oxygens) atoms remain practically unaffected. Nevertheless the last show a deviation compared to previous measurements on the R123 samples. On the other hand, the changes induced in the B-lg Raman active mode of O(2, 3) (out-of-phase vibrations), can be attributed to chemically separated phases rich in either La, R or an intermediate phase, The results are discussed in connection with a previously studied Pr(0.5)R(0.5)Ba(2)Cu(3)O(y) series. (C) 1997 Academic Press Limited.