The impact of chemical short-range order on the thermophysical properties of medium- and high-entropy alloys

The unusual behavior observed in the coefficient of thermal expansion and specific heat capacity of CrFeNi, CoCrNi, and CoCrFeNi medium/high-entropy alloys is commonly referred to as the K-state effect. It is shown to be independent of the Curie temperature, as demonstrated by temperature-dependent magnetic moment measurements. CoCrFeNi alloy is chosen for detailed characterization; potential reasons for the K-state effect such as texture, recrystallization, and second-phase precipitation are ruled out. An examination of the electronic structure indicates the formation of a pseudo-gap in the Density of States, which suggests a specific chemical interaction between Ni and Cr atoms upon alloying. Hybrid Monte Carlo/Molecular Dynamic (MC/MD) simulations indicate the presence of non-negligible chemical short-range order (CSRO). Local lattice distortions are shown to be negligible, although deviations around Cr and Ni elements from those expected in a fully disordered structure are experimentally observed by X-ray absorption spectroscopy. The determined bonding distances are in good agreement with MC/MD calculations. A mechanism is proposed to explain the anomalies and calorimetric experiments and their results are used to validate the mechanism

Inhibition of Oxygen Scavenging by TiN at the TiN/SiO2 Interface by Atomic-Layer-Deposited Al2O3 Protective Interlayer

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Characterization of Y and Mn co-substituted BaZrO3 ceramics: Material properties as a function of the substituent concentration

Innovations in materials science are the key element for solving technological challenges. Various energy and environmental applications require designing materials with tailored compositions, microstructures and specific target-oriented performance. Y and Mn co-substituted BaZrO, e.g. BaZrYMnO, has previously attracted attention as a membrane material for H separation from gas mixtures due to its mixed proton-electron conductivity leading to appreciable levels of H-flux at elevated temperatures and its good thermo-chemical stability under reducing environments. In the present work, we developed ceramic materials within the BaZrYMnO series, where x = 0.02–0.15. The study of their functional properties in dependence of the Y-to-Mn ratio disclosed that thermal expansion and hydration decrease by increasing the Mn content as well as the total electrical conductivity. In addition to that, XPS analysis and near edge X-ray absorption fine structure spectra (NEXAFS) in the vicinity of O K-edge and Mn L-edges indicated that the Mn atoms oxidation state in the surface and in the bulk range from Mn to Mn depending on the ambient conditions that can be encountered in MPEC electrodes, which it is suggested to be related with a hydration mechanism mediated by Mn oxidation and subsequent proton attachment to oxygen neighbors, similar to LSM

Characterization of Y and Mn co-substituted BaZrO3 ceramics: Material properties as a function of the substituent concentration

Innovations in materials science are the key element for solving technological challenges. Various energy and environmental applications require designing materials with tailored compositions, microstructures and specific target-oriented performance. Y and Mn co-substituted BaZrO3, e.g. BaZr0.85Y0.15Mn0.05O3-δ, has previously attracted attention as a membrane material for H2 separation from gas mixtures due to its mixed proton-electron conductivity leading to appreciable levels of H2-flux at elevated temperatures and its good thermo-chemical stability under reducing environments. In the present work, we developed ceramic materials within the BaZr0.8Y0.2-xMnxO3-δ series, where x = 0.02–0.15. The study of their functional properties in dependence of the Y-to-Mn ratio disclosed that thermal expansion and hydration decrease by increasing the Mn content as well as the total electrical conductivity. In addition to that, XPS analysis and near edge X-ray absorption fine structure spectra (NEXAFS) in the vicinity of O K-edge and Mn L2,3-edges indicated that the Mn atoms oxidation state in the surface and in the bulk range from Mn2+ to Mn4+ depending on the ambient conditions that can be encountered in MPEC electrodes, which it is suggested to be related with a hydration mechanism mediated by Mn oxidation and subsequent proton attachment to oxygen neighbors, similar to LSM

The impact of chemical short-range order on the thermophysical properties of medium- and high-entropy alloys

The unusual behavior observed in the coefficient of thermal expansion and specific heat capacity of CrFeNi, CoCrNi, and CoCrFeNi medium/high-entropy alloys is commonly referred to as the K-state effect. It is shown to be independent of the Curie temperature, as demonstrated by temperature-dependent magnetic moment measurements. CoCrFeNi alloy is chosen for detailed characterization; potential reasons for the K-state effect such as texture, recrystallization, and second-phase precipitation are ruled out. An examination of the electronic structure indicates the formation of a pseudo-gap in the Density of States, which suggests a specific chemical interaction between Ni and Cr atoms upon alloying. Hybrid Monte Carlo/Molecular Dynamic (MC/MD) simulations indicate the presence of non-negligible chemical short-range order (CSRO). Local lattice distortions are shown to be negligible, although deviations around Cr and Ni elements from those expected in a fully disordered structure are experimentally observed by X-ray absorption spectroscopy. The determined bonding distances are in good agreement with MC/MD calculations. A mechanism is proposed to explain the anomalies and calorimetric experiments and their results are used to validate the mechanism