Oxygen surface exchange kinetics and electronic conductivity of the thirdorder Ruddlesden-Popper phase Pr4Ni2.7Co0.3O10-δ

The third-order Ruddlesden-Popper phase Pr ₄Ni _2.7Co _0.3O _10-δ (PNCO43) was synthesized by a freeze drying process. Phase purity and crystal structure were determined by X-ray diffraction and Rietveld analysis. The electronic conductivity of a bulk sample obtained by a two-step sintering process was measured by the four-point dc van der Pauw method as a function of temperature (50 ≤ T/°C ≤ 800) and oxygen partial pressure (1 × 10 ^{− 3} ≤ pO ₂/bar ≤1). Dense thin-film PNCO43 microelectrodes were prepared by pulsed laser deposition and photolithography on yttria-stabilised zirconia substrates. The thin-films were characterized by X-ray diffraction, scanning electron microscopy, scanning transmission electron microscopy, and inductively coupled plasma optical emission spectroscopy. Individual resistive and capacitive processes were investigated with electrochemical impedance spectroscopy as a function of the oxygen partial pressure (1 × 10 ^{− 3} ≤ pO ₂/bar ≤1) and temperature (600 ≤ T/°C ≤ 850). Oxygen surface exchange coefficients k ^q, calculated from the resistance of the electrode, show relatively high values (e.g. k ^q = 1.5 × 10 ^{− 6} cm s ⁻¹ at 800 °C and 2 × 10 ^{− 1} bar pO ₂). Chemical surface exchange coefficients k _chem of oxygen were obtained from the peak frequency or the chemical capacitance as determined by impedance spectroscopy.