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Enhanced ionic mobility in mixed ionic and electronic conducting solids contributes to improved performance of memristive memory, energy storage and conversion, and catalytic devices. Ionic mobility can be significantly depressed at reduced temperatures, for example, due to defect association and therefore needs to be monitored. Measurements of ionic transport in mixed conductors, however, proves to be difficult due to dominant electronic conductivity. This study examines the impact of different levels of quenched‐in oxygen deficiency on the oxygen vacancy mobility near room temperature. A praseodymium doped ceria (Pr0.1Ce0.9O2–δ) film is grown by pulsed laser deposition and annealed in various oxygen partial pressures to modify its oxygen vacancy concentration. Changes in film non‐stoichiometry are monitored by tracking the optical absorption related to the oxidation state of Pr ions. A 13‐fold increase in ionic mobility at 60 °C for increases in oxygen non‐stoichiometry from 0.032 to 0.042 is detected with negligible changes in migration enthalpy and large changes in pre‐factor. Several factors potentially contributing to the large pre‐factor changes are examined and discussed. Insights into how ionic defect concentration can markedly impact ionic mobility should help in elucidating the origins of variations seen in nanoionic devices. [ABSTRACT FROM AUTHOR]

Mixed ionic–electronic conductors offer chemical and electrical means for active tuning of their optical constants, e.g., with variations in oxygen non‐stoichiometry in Pr0.1Ce0.9O2–δ, enabling implementation of adaptive thin film optical devices. In situ chemo‐tuning of the extinction coefficient in Pr0.1Ce0.9O2–δ at elevated temperatures is demonstrated and a tuning model is provided that treats the interdependence of mobile oxygen vacancies and small polarons coupled to variations in optically active praseodymium ions. Furthermore, a new means for electro‐tuning of the optical constants of mixed ionic–electronic conductors is demonstrated experimentally and modeled for Pr0.1Ce0.9O2–δ thin films deposited on grid‐like electrode structures. Modeling of non‐steady‐state optical transmittance modulations in the latter allows for estimation of oxygen vacancy mobility that determines the switching speed of the device. Quenched‐in values of nr and k to room temperature become nonvolatile, providing a modulation range in the extinction coefficient of Δk ≈ 0.1 (change of ≈800%) and in the refractive index of Δnr ≈ 0.1 (relative to initial nr of ≈2.35). Key figures of merit, including transmission optical modulation of ≈0.04 per 1 mV nm–1, switching energy per area of 1.9 nJ µm–2, and switching times of seconds, are demonstrated, with further improvements possible. [ABSTRACT FROM AUTHOR]

Solid‐state mixed ionic–electronic conductors (MIECs) in which ionic transport is commonly accompanied by predominant electronic conductivity underpin key technologies and require universal characterization methods for monitoring transport at the nanoscale, at both high and near ambient temperatures, the latter being especially challenging. In this study, a novel dynamic current–voltage analysis technique is utilized to decouple ionic and electronic transport properties from each other. The versatility of the method is demonstrated by enabling measurement of the oxygen vacancy mobility in Pr0.1Ce0.9O2−δ thin films, across an unusually wide temperature range, from 35 to 500 °C. Despite the presence of predominant electronic conduction, the oxygen vacancy mobility in Pr0.1Ce0.9O2−δ is measured, being 6.8 × 10−6 cm2 V−1 s−1 at 500 °C, decreasing by seven orders of magnitude down to 35 °C, and following a single thermal activation energy of 0.82 ± 0.02 eV. A comparison with previous reports on oxygen vacancy transport and with the one derived in this study from impedance spectroscopy, interpreted with the Jamnik–Maier model, further confirms the dynamic current–voltage analysis results. This method can more generally be applied to other types of MIECs, thereby enabling deeper insights into mobile ionic defect transport and accompanying thermodynamic properties. [ABSTRACT FROM AUTHOR]

Determining the ionic mobility in solids is often challenging due to inherently low ionic conductivities, typically requiring measurements at elevated temperatures, with high impedance analyzers and/or extended resistivity transients. Moreover, in many solids, the ionic conductivity is masked by dominant electronic conductivity, characterized by much higher carrier mobility. By focusing our measurements on nano-dimensioned thin films, we are able to overcome such limitations. First, measurement time and temperature can be reduced, the latter to near ambient conditions, in selected materials, due to the considerably faster response of thin films compared to bulk materials to applied electrical stimulus. Second, the effect of the redistribution of ionic defects on the nano-scale, at relatively short time, has a major impact on the total conductivity. The proposed method relies on measuring the nonlinear I - V response of thin films to linear voltage sweeps of high amplitude (relative to the thermal voltage) at different sweep rates. This differs from the impedance spectroscopy technique that analyzes the small signal response of systems. The method also differs from the well-known technique of cyclic voltammetry for deriving ion diffusion coefficients, as it does not require redox reactions to take place during voltage sweeps, thereby making it more generally applicable. In this work, we present a novel and simple method for determining the ionic mobility from the measured I-V relations. It is determined from the position of a peak in the I-V relations and the sweep rate. The mobility so derived is compared with the one obtained by fitting the I-V relations based on solving the drift-diffusion equations for ions and electrons as published recently. Though the near ambient temperature ionic mobility was found to be seven orders of magnitude lower than the corresponding electronic one, it could nevertheless be well deconvoluted and characterized by both methods. The experimental results are compared with previous measurements on bulk and powder samples of molybdenum trioxide. [ABSTRACT FROM AUTHOR]