The effect of chemical and mechanical lattice strain on the transport properties of thin film and bulk PrCoO3-δ

Abstract

The aim of this work is to investigate: enhancement of the oxygen reduction reaction at the PrCoO3-δ/Pr2NiO4+ δ (PCO113/PNO214), inteface; and the mechano-chemical effect in mechanically strained lattice mismatched PCO113 films on Ce0.9Gd0.1O2/8-mol% YSZ(002) fabricated using pulsed laser deposition, PLD, and chemically strained A-site deficient PCO113 (Pr1-xCO3- δ) samples. PCO113 films on Si(004) and Ce0.9Gd0.1O2(200)/8-mol% YSZ(002) single crystal substrates were deposited by PLD. Out-of-plane compressive PCO113 lattice strains, calculated from the PCO113(002) reflection, between -0.39% to -0.99% were measured. Single phase PNO214 films could not be deposited for the PLD conditions tested in this work. Isothermal measurements of PNO214 at 800°C in air showed the gradual formation of Pr6O11 and Pr4Ni3O10, suggesting that this process is kinetically limited. Subsequently, investigation of the mechano-chemical effect was limited to the mechanically and chemically strained PCO113 systems. The chemical expansion on introducing Pr-deficiency, x, in PCO113 was attributed to the formation of Pr vacancies, which effect was large enough to offset the decrease in ionic radii as the oxidation state of Co3+ increased to Co4+. High temperature XRD indicated a thermo-chemical expansion wherein oxygen uptake at high temperatures affected the expansion of the PCO113 lattice as a function of temperature. A comparison of the thermos-chemical expansion between the Pr-deficient PCO113 samples confirmed an increase in oxygen vacancy concentration with Pr-deficiency. 18O diffusion profiles of the Pr-deficient PCO113 samples were fitted using Crank's solution for diffusion in a semi-infinite plane. D* and k* values varied between 1.36-2.26 ×10-16 cm2/s and 4.48-10.1×10-10 cm/s. D* and electrical conductivity was found to increase with Pr-deficiency. Visual analysis of 18O diffusions profiles of the strained PCO113 films suggested that the mechano-chemical effect was present and the introduction of a compressive out-of-plane strain inhibited oxide ion diffusion.