Atomic distribution, local structure and cation size effect in o-R1-xCaxMnO3 (R = Dy, Y, and Ho).

We propose new interatomic potentials for the small rare-earth-based orthorhombic RMnO3 (R = Dy, Y, Ho), which accurately model the structural properties of these extreme cases of lanthanide manganate series. They are further employed to investigate the intrinsic defects in o-RMnO3 and the cation distribution and local structure in o-R1-xCaxMnO3 (R = Dy, Y, Ho). Schottky disorders are found to be the dominant structural defects, and the possibility of a small degree of anti-site disorder of R and Mn ions over A and B sites is found. The introduced Ca dopants tend to form chemically and structurally like CaMnO3 clusters in the lightly doped system, which can be regarded as representations of microscopic phase separation. The local structural disorder is reduced with increasing doping density. For o-R0.5Ca0.5MnO3 (R = Dy, Y, Ho), the charge ordering state is intrinsically favored, and the layer stripe model is shown to be energetically more favorable and structurally more reasonable. Moreover, the tendency to form charge ordered stripes increases with the decrease of R size. The local structure in the layer stripe pattern deviates largely from the average structure: RMnO3-like and CaMnO3-like layers are formed. The size of R ion has a significant influence on the doping effect on Jahn-Teller (JT) distortion and a manganate with a larger R will experience a larger reduction on the anisotropy of Mn-O bonds in Mn(3+)O6 octahedra. However, the change of octahedral tilting upon doping does not vary much with R radii.