Realizing Metastable Cobaltite Perovskite via Proton-Induced Filling of Oxygen Vacancy Channels

Fe-Doped SrCoOx FET Sensors for Extreme Alkaline pH Sensing

The accurate measurement of pH in highly alkaline environments is critical for various industrial applications but remains a complex task. This paper discusses the development of novel Fe-doped SrCoOx-based FET sensors for the detection of extreme alkaline pH levels. Through a comprehensive investigation of the effects of Fe doping on the structure, electrical properties, and sensing performance of SrCoOx, we have identified the optimal doping level that significantly enhances the sensor's performance in highly alkaline conditions. With a Fe doping level of 5 mol %, the sensitivity of the sensor improves to 0.86 lg(Ω)/pH while maintaining the response rate. Further increasing the Fe doping to 10 mol % results in a sensor that demonstrates favorable response time, a suitable pH range, and a linear correlation between lg(R) and pH. The combination of X-ray photoelectron spectroscopy and X-ray diffraction analysis provides insight into the regulation mechanisms of Fe doping on the crystal structure, electronic structure, and oxygen vacancy concentration of SrCoOx. Our findings indicate that Fe doping leads to an increase in oxygen vacancy concentration and a decrease in the energy barrier for oxygen ion migration, which contributes to the improved sensing performance of the Fe-doped SrCoOx sensors. Additionally, the study highlights the influence of oxygen vacancy concentration on the electrical properties of SrCoOx. Precise control over the concentration of oxygen vacancies is crucial for optimizing the sensitivity and response speed of SrCoOx FET sensors under extreme alkalinity conditions.

Highly efficient and fast modulation of magnetic coupling interaction in the SrCoO2.5/La0.7Ca0.3MnO3 heterostructure

Effective manipulation of magnetic properties in transition-metal oxides is one of the crucial issues for the application of materials. Up to now, most investigations have focused on electrolyte-based ionic control, which is limited by the slow speed. In this work, the interfacial coupling of the SrCoO2.5/La0.7Ca0.3MnO3 (LCMO) bilayer is effectively modulated with fast response time. After being treated with diluted acetic acid, the bilayer changes from antiferromagnetic/ferromagnetic (AFM/FM) coupling to FM/FM coupling and the Curie temperature is also effectively increased. Meanwhile, the corresponding electric transport properties are modulated within a very short time. Combined with the structure characterization and X-ray absorption measurements, we find that the top SrCoO2.5 layer is changed from the antiferromagnetic insulator to the ferromagnetic metal phase, which is attributed to the formation of the active oxygen species due to the reaction between the protons in the acid and the SrCoO2.5 layer. The bottom LCMO layer remains unchanged during this process. The response time of the bilayer with the acid treatment method is more than an order of magnitude faster than other methods. It is expected that this acid treatment method may open more possibilities for manipulating the magnetic and electric properties in oxide-based devices.

Strain-Induced Uphill Hydrogen Distribution in Perovskite Oxide Films

Incorporating hydrogen into transition-metal oxides (TMOs) provides a facile and powerful way to manipulate the performances of TMOs, and thus numerous efforts have been invested in developing hydrogenation methods and exploring the property modulation via hydrogen doping. However, the distribution of hydrogen ions, which is a key factor in determining the physicochemical properties on a microscopic scale, has not been clearly illustrated. Here, focusing on prototypical perovskite oxide (NdNiO3 and La0.67Sr0.33MnO3) epitaxial films, we find that hydrogen distribution exhibits an anomalous "uphill" feature (against the concentration gradient) under tensile strain, namely, the proton concentration enhances upon getting farther from the hydrogen source. Distinctly, under a compressive strain state, hydrogen shows a normal distribution without uphill features. The epitaxial strain significantly influences the chemical lattice coupling and the energy profile as a function of the hydrogen doping position, thus dominating the hydrogen distribution. Furthermore, the strain-(H+) distribution relationship is maintained in different hydrogenation methods (metal-alkali treatment) which is first applied to perovskite oxides. The discovery of strain-dependent hydrogen distribution in oxides provides insights into tailoring the magnetoelectric and energy-conversion functionalities of TMOs via strain engineering.

Protonation-Induced Colossal Lattice Expansion in La2/3Sr1/3MnO3

Ion injection controlled by an electric field is a powerful method to manipulate the diverse physical and chemical properties of metal oxides. However, the dynamic control of ion concentrations and their correlations with lattices in perovskite systems have not been fully understood. In this study, we systematically demonstrate the electric-field-controlled protonation of La2/3Sr1/3MnO3 (LSMO) films. The rapid and room-temperature protonation induces a colossal lattice expansion of 9.35% in tensile-strained LSMO, which is crucial for tailoring material properties and enabling a wide range of applications in advanced electronics, energy storage, and sensing technologies. This large expansion in the lattice is attributed to the higher degree of proton diffusion, resulting in a significant elongation in the Mn-O bond and octahedral tilting, which is supported by results from density functional theory calculations. Interestingly, such a colossal expansion is not observed in LSMO under compressive strain, indicating the close dependence of ion-electron-lattice coupling on strain states. These efficient modulations of the lattice and magnetoelectric functionalities of LSMO via proton diffusion offer a promising avenue for developing multifunctional iontronic devices.