We present a study of the Raman phonons in YBa2(Cu0.96Ni0.04)(4)O-8 under hydrostatic pressure in the superconducting phase. A comparison with our earlier work on the undoped YBa2Cu4O8 shows that the pressure coefficients of two vibrational modes involving oxygen atoms differ significantly from those of the corresponding modes in the undoped material. These are the O(1) chain mode which shifts 33% faster and the O(2)-O(3) in-phase mode which shifts 23% slower than the undoped counterparts. The other Raman modes in the Ni-doped sample shift in a manner similar to the undoped material. The observed behavior of the O(1) chain and O(2)-O(3) in-phase modes in YBa2(Cu0.96Ni0.04)(4)O-8 under pressure and;the softening of the Cu(1) A(g) mode frequency with increasing Ni doping suggest that the Ni atoms substitute for the Cu atoms in the chain, which in rum decreases the compressibility in the vicinity of the Cu(Ni) chain atom. [S0163-1829(99)14429-1].

We present a study of the Raman phonons in YBa2 (Cu0. 96Ni0. 04) 4O8 under hydrostatic pressure in the superconducting phase. In contrast to the undoped material, two modes have significantly different pressure coefficients: the O (1) chain mode shifts 35% faster while the O (2) -O (3) in phase mode shifts 33% slower than their undoped counterparts. The other modes shift in a manner similar to the undoped material. We understand this behavior in terms of the smaller compressibility in the vicinity of the chain substituted Cu (Ni) atom.

We report a Raman scattering study of YBa2(Cu1−xMx)4O8 (M=Ni, Zn) ceramic samples in the normal and superconducting phases. The frequency of the Cu(1) chain Ag mode is observed to soften by about 11 cm−1 over a Ni doping range of 0–2.5%, while other modes exhibit shifts of 0–4 cm−1. The modes show only small shifts in the Zn doped materials. We believe that this large softening indicates that Ni substitutes for Cu in chain sites.