Effect of oxygen stoichiometry on softening of Raman active lattice modes in YBa2Cu3Ox

Temperature-dependent frequency-shift and linewidth data of the Raman active 337-cm-1 CuO2 in-plane bond-bending mode have been measured for five different oxygen stoichiometries between x=7.00 and x=6.14 in polycrystalline samples. Softening and line-broadening effects observed for the x=7.00 sample are sharply reduced for x=6.87 even though the superconducting transition temperature is similar. With a further reduction of oxygen content below x=6.68 both the soft-mode behavior and the line-broadening effects completely disappear. These unexpected results could suggest a large variation in the interaction between the electronic system and the lattice as the oxygen content is varied. © 1988 The American Physical Society.