Er2BaNiO5 has been reported recently as a magneto-electric material, displaying a spontaneous polarization at T=55K, followed by a transition to a collinear antiferromagnetic state at 32K. The structural displacement associated with the spontaneous polarization is reported to involve a displacement of the oxygen octahedral around the Ni ions. We have prepared large high quality single crystals of ErBaNiO5 and we propose here to perform a structural study of Er2BaNiO5 around the ferro-electric and magnetic transition temperatures in order to directly observe the oxygen displacements and look for signs of magneto-elastic coupling. We will require 2 days of beam time on SXD to complete this study.