STRUCTURAL-CHANGES AND RELATED EFFECTS DUE TO CHARGE ORDERING IN ND0.5CA0.5MNO3

Charge ordering in L(1-x)A(x)MnO(3) (L=rare earth, A=Ca,Sr) depends st rongly on the width of the e(g) band or on the average radius of the A -site cations, [r(A)]. Investigations of Nd0.5Ca0.5MnO3 with a small [ r(A)] show evidence for a first -order transition due to charge orderi ng around 220 K, accompanied by a large decrease in volume (0.45%). St ructural data at different temperatures indicate that the distortions within the structure are a direct result of charge ordering. Valence s um calculations show the presence of two differently charged Mn atoms. Electron transport and magnetic susceptibility measurements have been carried out down to low temperatures to understand the nature of the charge-ordered state. The charge-ordered state melts on the applicatio n of a magnetic field.