Atomically layer-by-layer diffusion of oxygen/hydrogen in highly epitaxial PrBaCo2O5.5+δ thin films

Abstract

Single-crystalline epitaxial thin films of PrBaCo2O5.5+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 °C. During the oxidation cycle under O2, the PrBCO films exhibit fast oscillations in their dR(t)/dt vs. t plots, which reflect the oxidation processes, Co2+/Co3+ → Co3+ and Co3+ → Co3+/Co4+, 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)(CoO2)(PrO)(CoO2) 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.

Anomalous Resistance of LBCO Gas Sensors Induced by Electro-Catalyzed Surface O-H Reactions

“…In this work, we studied the gas sensing properties of a LBCO thin film epitaxially grown on MgO (001) substrate by PLD. The film demonstrated anomalous sensor behavior similar to previous reports, 28,29 and such behavior was compared for different atmospheres of O 2 /4% H 2 + 96% N 2 , O 2 /N 2 , and O 2 /Ar at temperatures ranging from 300 °C to 800 °C. The LBCO sensor in the O 2 /H 2 atmosphere demonstrates anomalous time-dependent resistance at low temperatures and extremely high resistance in the full range of temperature (300 °C-800 °C).…”

“…25,26 In addition, when the ambient of LnBCO is switched between O 2 and a gas mixture of 4% H 2 + 96% N 2 , the sheet resistance of LnBCO can reproducibly change over 99% in a few seconds. [27][28][29][30][31] In particular, when switching from O 2 to H 2 or vice versa, LnBCO exhibits an anomalous sensor behavior at below ∼400 °C, 28,29 where the resistance is time-dependent with a sharp maximum; such behavior disappears at above 400 °C. This temperature-dependent anomalous sensor response has thus gathered our attention since it may offer insight towards the physical chemistry of LnBCO surface not only scientifically interesting but also technically important for the design and applications of LnBCO-based gas sensors.…”

Roles of reaction kinetics of CO2 on a PrBaCo2O5.5+δ surfaces

“…The resistance of reduced PBCO is 5 orders larger than that of oxidized one. 39 Accordingly, we assume that the conductivity of the electrode is linearly proportional to the oxygen vacancy concentration, which is uniformly distributed inside the dense thin lm electrodes. The rates of both the forward and backward surface reactions are taken to be unity since the processing was taken in the near equilibrium.…”

Compressive Strain-Tuned Epitaxial Nature and Physical Properties of Double-Perovskite PrBaCo2O5.5+δ Thin Films

“…Besides the sensitivity of the copper oxide superconductivity, perovskite cobaltates are the systems that are extensively susceptible to the oxygen content for the different oxidation states of cobalt (Co 2+ , Co 3+ , and Co 4+ ) and electronic spin states. , Among them, the oxygen-deficient double-perovskite structures with the formula of RBaCo 2 O 5.5+δ (RBCO, R = rare earth cations) become the fascinating family in the tunable multifunctional materials because of the peculiar order–disorder at the A-site and their excellent mixed ionic/electronic conductivity. This makes them suitable for many practical applications in solid oxide fuel cells, separation membranes, gas sensors, and transducers among others. − In particular, double-perovskite PrBaCo 2 O 5.5+δ (PBCO) is one of the most intriguing materials for its fast oxygen kinetics at intermediate temperatures and sensitivity of physical properties to the oxygen content. ,− …”