Infrared spectroscopic study of the local structural changes across the metal insulator transition in nickel-doped GdBaCo2O5.5

Phonons in GdBaCo2O5.5 have been identified using infrared spectroscopy and their mode assignments have been carried out using ab initio lattice dynamical calculations. Metal insulator transitions in undoped and nickel-doped GdBaCo2O5.5 have been probed using infrared absorption spectroscopy. The phonon modes corresponding to the bending mode of the CoO6 octahedra/pyramids are seen to soften, broaden and develop an asymmetry across the insulator–metal transition pointing to extensive electron phonon interaction effects in these systems. Correlated changes of the phonon line shape parameters associated with the transition indicate a suppression of TMIT with increased nickel doping of the cobalt sublattice. Temperature dependence of the octahedral stretching mode frequencies in undoped GdBaCo2O5.5 points to distinct structural distortions accompanying the high temperature metallic transition.