Crystal structure and electronic transport property of perovskite manganese oxides with a fixed tolerance factor

The structural and electronic transport properties of ABO3-type compounds La2/3−xRxCa1/3MnO3(R=Pr, Nd, Sm, Eu, Gd, Tb, Dy, Y, Er, and Tm) with a fixed tolerance factor of t=0.91137 is studied. Similar structure deformation, characterized by the nearly constant average Mn–O, A–O distances and Mn–O–Mn bond angles, is observed in different compounds. The metal–semiconductor transition shows a strong R dependent feature. The transition temperature decreases monotonously from 187 to 77.6 K as R varies from Tm to Pr, with a corresponding maximum resistivity ranging from 2.34 to 6.17×104 Ω cm. Very different magnetoresistance effects are also observed in this series of compounds. By assuming the presence of inhomogeneous local lattice distortions due to ions with different sizes at A sites and their mismatch with B ions, the lattice effects can be understood qualitatively.