Charge ordering in electron-doped manganates

Abstract

Electron-doped rare-earth manganates of the type Ca_1−xLn_xMnO₃ (Ln=La, Nd, Gd or Y) with x=0.2 and 0.3 show charge ordering in the 150-270 K range, but the charge-ordering transition temperature, T_co, generally decreases with the decrease in the size of the A-site cations, a trend exactly opposite to that for hole-doped manganates. On the other hand, T_co increases with x or the electron concentration. These trends are also seen for Ca_1−xLn_xMnO₃ compounds (T_co=300K for x=0.3) which show transitions to a more distorted orthorhombic structure below T_co. In Ca_1−xLn_xMnO₃, Cr doping does not melt the charge-ordered state, unlike the case for the hole-doped systems. CaMnO_2.82, for which electron doping is affected by anion vacancies, appears to show charge ordering at around 200 K.