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

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)MnO(3) (L = rare earth, A = alkaline 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 Angstrom, reveal that the charge-ordering transition temperature, T-CO, is not very sensitive to the size mismatch unlike ferromagnetic T-C or metal-insulator transition data. Furthermore, T-CO is not affected greatly by the orthorhombic lattice distortion. The observed decrease in T-CO with increase in < r(A)> is consistent with a quadratic dependence upon (r(A)(0) - < r(A)>) where r(A)(0) = 1.13 Angstrom.