Effect of the cation size disorder on charge ordering in rare-earth manganates

Abstract

The effect of disorder arising from the mismatch between the average sizes of the A-site cations in the rare-earth manganates, $L_{0.5}{A}_{0.5}{\mathrm{MnO}}_3$ $(L=\mathrm{rare}\mathrm{}\mathrm{earth},$ $A=\mathrm{alkaline}\mathrm{}\mathrm{earth})$, on their charge-ordering behavior has been investigated. Measurements on two series of manganates with a fixed average cation radius, $〈r_A〉,$ of 1.17 and 1.24 Å, reveal that the charge-ordering transition temperature, $T_{\mathrm{CO}},$ is not very sensitive to the size mismatch unlike ferromagnetic $T_C$ or metal-insulator transition data. Furthermore, $T_{\mathrm{CO}}$ is not affected greatly by the orthorhombic lattice distortion. The observed decrease in $T_{\mathrm{CO}}$ with increase in $〈r_A〉$ is consistent with a quadratic dependence upon ${(r}_A^0-〈r_A〉)$ where $r_A^0=1.13\mathrm{}\AA .$