Crystalline structure and electrical properties of solid solutions YNixMn1-xO3

Solid solutions belonging to the Mn-rich region of the YNi X Mn 1-X O 3 system have been studied. The powders were prepared by solid state reaction between the corresponding oxides. Sintered ceramics were obtained by firing at 1325-1350°C. The incorporation of 20 atomic % Ni 2+ to the Yttrium manganite induces the formation of a perovskite phase, with orthorhombic symmetry. Increase of the Ni amount leads to an increase of the orthorhombicity factor b/a, up to an amount of 50 atomic % Ni 2+ . Above this Ni amount, a biphasic system has been observed, with the presence of unreacted Y 2 O 3 . DC electrical conductivity measurements have shown semiconducting behaviour for all the solid solutions with perovskite-type structure. The room temperature conductivity increases with Ni until ∼33 atomic % Ni, and then decreases. The 50/50 Ni/Mn composition has different values of conductivity and activation energy against those corresponding to samples with lower values of that ionic ratio. Small polaron hopping mechanism controls the conductivity in these ceramics. Results are discussed as a function of the Mn 3+ /Mn 4+ ratio for each composition.