Abstract
It has been documented that the total electrical conductivity of the hexagonal rare-earth manganites Y0.95Pr0.05MnO3+δ and Y0.95Nd0.05MnO3+δ, as well as the undoped YMnO3+δ, is largely dependent on the oxygen excess δ, which increases considerably at temperatures below ca. 300 °C in air or O2. Improvement for samples maintaining the same P63cm crystal structure can exceed 3 orders of magnitude below 200 °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 O2, and therefore indirectly influences the conductivity as well. At high temperatures (700–1000 °C) and in different atmospheres of Ar, air, and O2, 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 (δ ≈ 0), the mean ionic radius of Y1−xLnx appears to influence the electrical conductivity, with the highest values observed for the parent YMnO3. For Y0.95Pr0.05MnO3+δ 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+δ electrode document different behavior at higher and lower temperatures in air, corresponding to the total conduction characteristics.
Highlights
Multiferroic materials, showing the coexistence of ferroelectricity and magnetism, have become of special interest for physicists, due to fascinating and complex magnetoelectric properties and considering their possible application for data storage, capacitors, transducers, actuators, etc. [1,2]
P63 cm space group, associated with tilting of the oxygen bi-pyramids surrounding Mn ions, as well as bending the Y layers [8]. This can be considered as the asymmetric movement of Y3+ cations from their positions in the aristotype structure [9,10]
The magnetic properties reflect the presence of Mn3+ cations, which are ordered within the a-b planes, with the possible effect of canting of the Mn-related spins [7]
Summary
Multiferroic materials, showing the coexistence of ferroelectricity and magnetism, have become of special interest for physicists, due to fascinating and complex magnetoelectric properties and considering their possible application for data storage, capacitors, transducers, actuators, etc. [1,2]. P63 cm space group, associated with tilting of the oxygen bi-pyramids surrounding Mn ions, as well as bending the Y layers [8]. This can be considered as the asymmetric movement of Y3+ cations from their positions in the aristotype structure [9,10]. The five-fold coordination of Mn3+ results in the splitting of the 3d4 electronic orbitals into three sets: empty a’, and filled up e’, and e”. This corresponds to the high spin state, with all other orbitals being occupied by one electron except for a’ (dz ). Some LnMnO3 oxides can be obtained (under special conditions) in the perovskite-type structure, showing distinctively different electronic properties [11]
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