Evidences for non-equivalent centers in mixed chain nickelates (NdxY1−x)2BaNiO5

Absorption spectra of the mixed chain nickelates (NdxY1−x)2BaNiO5 were measured for different x. Experimentally two evidences for the presence of non-equivalent rare-earth centers (NEREC) were found. First, the linewidths show a very strong broadening for x when the calculated distribution over NEREC is wide. Second, a complicated lineshape of the lowest-frequency line in the region of the 4I9/2→4I11/2 electronic transition is in good agreement with statistics of NEREC. A simple modeling for the line broadening due to NEREC is suggested.