LATTICE EFFECTS ON THE CHARGE-ORDERING TRANSITION IN R0.5SR1.5MNO4

Magnetic and transport properties are investigated for single crystals of layered-type-doped manganites R0.5Sr1.5MnO4 with systematic variat ion of the averaged radius r(R) of the trivalent rare-earth ions R3+ L a0.5Sr1.5MnO4 (R = La) shows a charge-ordering (CO) transition at T-CO = 230 K. With a decrease of the in-plane Mn-O bend length d(Mn-O(in)) , T-CO decreases and eventually the transition disappears for R = Nd. Such a remarkable lattice effect on the CO transition is in sharp cont rast to the negligible lattice effect in the isostructural layered nic kelates.