Influence of Doping on the Transport Properties of Y1-xLnxMnO3+δ (Ln: Pr, Nd)

It has been documented that the total electrical conductivity of the hexagonal rare-earth manganites Y0.95Pr0.05MnO3+delta and Y0.95Nd0.05MnO3+delta, as well as the undoped YMnO3+delta, is largely dependent on the oxygen excess delta, which increases considerably at temperatures below ca. 300 degrees C in air or O-2. Improvement for samples maintaining the same P6(3)cm crystal structure can exceed 3 orders of magnitude below 200 degrees C and is related to the amount of the intercalated oxygen. At the same time, doping with Nd3+ or Pr3+ affects the ability of the materials to incorporate O-2, and therefore indirectly influences the conductivity as well. At high temperatures (700-1000 degrees C) and in different atmospheres of Ar, air, and O-2, all materials are nearly oxygen-stoichiometric, showing very similar total conduction with the activation energy values of 0.8-0.9 eV. At low temperatures in Ar (delta approximate to 0), the mean ionic radius of Y(1-x)Ln(x) appears to influence the electrical conductivity, with the highest values observed for the parent YMnO3. For Y0.95Pr0.05MnO3+delta oxide, showing the largest oxygen content changes, the recorded dependence of the Seebeck coefficient on the temperature in different atmospheres exhibits complex behavior, reflecting oxygen content variations, and change of the dominant charge carriers at elevated temperatures in Ar (from electronic holes to electrons). Supplementary cathodic polarization resistance studies of the Y0.95Pr0.05MnO3+delta electrode document different behavior at higher and lower temperatures in air, corresponding to the total conduction characteristics.