Microstructure Related to Charge and Orbital Ordering in Pr sub (0.5) Ca sub (0.5) MnO sub 3

We have investigated the microstructure related to the charge and orbital ordering in the manganites Pr sub (0.5) Ca sub (0.5) MnO sub 3 by transmission electron microscopy. Electron diffraction clearly shows the presence of the incommensurate structure in the paramagnetic insulator phase of Pr sub (0.5) Ca sub (0.5) MnO sub 3 between 180K and 260K. Our experimental results clearly show that the incommensurate-to-commensurate (IC-to-C) charge-ordering transition was correspondent with the paramagnetic of antiferromagnetic transition around 180K. Dark field images also revealed the motion of the discommensurations during the IC-to-C transition. A model of the IC structure which involves the presence of the partial orbital disordering and the complete charge ordering is proposed.