Oxygen surface exchange kinetics and electronic conductivity of the third-order Ruddlesden-Popper phase Pr₄Ni_2.7Co_0.3O_10-δ

The third-order Ruddlesden-Popper phase Pr₄Ni_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} ≤ pO₂/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} ≤ pO₂/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 pO₂). Chemical surface exchange coefficients k_chem of oxygen were obtained from the peak frequency or the chemical capacitance as determined by impedance spectroscopy.