Mixed ionic-electronic conductors are of great interest for development of oxygen separation membranes and air electrodes for intermediate temperature solid oxide fuel and electrolysis cells. This work presents the results of studying the structure, transport properties and oxygen mobility in Nd2-xCaxNiO4 oxides (x = 0-0.5), synthesized via a solution-assisted solid state reaction method, in correlation with the over-stoichiometric oxygen content. High oxygen mobility was demonstrated in the low-doped materials (D-o similar to 10(-10)-10(-8) CM2/S at 700 degrees C) which corresponded to the ionic (oxygen) conductivity values similar to 10(-4)-10(-2) S/cm, comparable to those for widely used solid electrolytes and state-of-the-art cathode materials. The polarization resistance of the Nd2-xCaxNiO4+delta electrodes in contact with Ce0.8Sm0.2O1.9 electrolyte was shown to have non-linear dependency on Ca content, which may be caused by the influence of two opposite tendencies for decreasing overstoichiometric oxygen and oxygen diffusivity and increasing the total conductivity with Ca doping. High electrical and electrochemical characteristics along with oxygen mobility mean the materials developed display high potential for electrochemical and catalytic applications.