Electric transport properties of rare earth doped YbxCa1-xMnO3 ceramics (part III: Point defect chemistry).

A defect chemical model based on charge neutrality and laws of mass action is proposed to clarify the details of the chemistry of point defects for donor-doped Yb x Ca 1-x MnO 3. DC-conductivity measurements were carried out in a wide range of partial pressure of oxygen p (O 2) ≈ 10−1 down to 10-19 MPa at 750⁰C for the first time without disintegrating the ceramic sample through reduction. A comparison of the experimental observations and the theoretical defect chemical models clearly shows the possibilities for controlling charge carriers in dependence of partial pressure of oxygen p (O 2) and dopant concentration. The origin of a plateau state, of a drastic decrease in conductivity in the intermediate and reduction p (O 2) regimes are figured out, respectively. In addition, the kind and concentration of the electronic and ionic majority charge carriers are determined and formulated according to the proposed defect chemical model. Furthermore, phase transitions were studied in a wide range of p (O 2) at elevated temperatures [ABSTRACT FROM AUTHOR]