EFFECT OF RARE EARTH IONIC RADIUS ON CHARGE ORDERING IN Y_(1-x)Gd_xBaCo_2O_5 LAYERED PEROVSKITE

The structural and transport properties of the layered cobalt oxide Y1-xGdxBaCo2O5(x=0,0.25,0.5,0.75,1) were investigated.From the evolution of the behavior between YBaCo2O5 and GdBaCo2O5 we have confirmed the existence of charge-ordering transition in GdBaCo2O5.It is also shown that the charge-ordering transition temperature rises with increasing the ionic radius of rare earth.