Atomically layer-by-layer diffusion of oxygen/hydrogen in highly epitaxial PrBaCo_2O_(5.5+δ) thin films

摘要

Single-crystalline epitaxial thin films of PrBaCo_2O_(5.5+δ) (PrBCO) were prepared, and their resistance R(t) under a switching flow of oxidizing and reducing gases were measured as a function of the gas flow time t in the temperature range of 200-800 ℃. During the oxidation cycle under O_2, the PrBCO films exhibit fast oscillations in their dR(t)/dt vs. t plots, which reflect the oxidation processes, Co~(2+)/Co~(3+) → Co~(3+) and Co~(3+) → Co~(3+)/Co~(4+), that the Co atoms of PrBCO undergo. Each oscillation consists of two peaks, with larger and smaller peaks representing the oxygen/hydrogen diffusion through the (BaO)(CoO_2)(PrO)(CoO_2) layers of PrBCO via the oxygen-vacancy-exchange mechanism. This finding paves a significant avenue for cathode materials operating in low-temperature solid-oxide-fuel-cell devices and for chemical sensors with wide range of operating temperature.