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Kinetics of Cr <sup>3+</sup> to Cr <sup>4+</sup> ion valence transformations and intra-lattice cation exchange of Cr <sup>4+</sup> in Cr,Ca:YAG ceramics used as laser gain and passive Q-switching media
摘要： This paper focuses on the kinetics of Cr4+ formation in Cr,Ca:YAG ceramics prepared by solid-state reaction sintering. The kinetics of Cr4+ formation was studied by annealing of Cr,Ca:YAG ceramics in ambient air under different temperatures at different times, resulting in the transformation of Cr3+ to Cr4+. The activation energy (Ea) of Cr3+ oxidation determined by the Jander model was 2.7 ± 0.2 eV, which is in good correlation with the activation energy of innergrain oxygen diffusion in the YAG lattice. It is concluded that Cr3+ to Cr4+ transformation in YAG ceramics is limited by oxygen diffusion through the grain body. It was established that in Cr,Ca:YAG ceramics, the intralattice cation exchange, in which the Cr4+ ions exchange positions with the Al3+ ions, switching from “A” to “D” sites, is faster than Cr3+ to Cr4+ oxidation. In the temperature range of 900–1300 ○C, the reaction enthalpy of Al3+/Cr4+ ion exchange between octahedral “A” and tetrahedral “D” lattice sites is close to zero, and this exchange ratio is thermodynamically driven by entropy.
关键词： intralattice cation exchange,Cr4+:YAG ceramics,solid-state reaction sintering,oxygen diffusion,Cr3+ oxidation
更新于2025-09-16 10:30:52
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Terahertz multi-band unidirectional reflectionless phenomenon in a MIM plasmonic waveguide system based on near-field coupling
摘要： Existing oil leakage detection approaches on the ocean or on the land have suffered from shortcomings like low-sensitivity, environment-vulnerability and high cost and energy consumption. A unique simple-structured upward open-channel microbial fuel cell (UOC-MFC) was developed to solve these challenges, in which the open-channel rolled cathode vertically floated on the electrolyte solution surface and simultaneously contacted with both air and water. Oil presence covered the cathode surface, blocked the oxygen diffusion on the cathode and thus caused the prompt drop of the potential readings of the UOC-MFC sensors. The oil shock tests using engine oil (EO) showed that the potential decrease and the response time exhibited excellent linear relationships (R2 > 0.99) with the EO amount, indicating a good sensitivity. Due to the separation of the anode and the invading oil, the UOC-MFC sensor recovered its external potential within 2.3 h after the EO shock tests, indicating a good reusability. The power density of the UOC-MFC was 450 mW/m3 under normal condition and dropped to 207 mW/m3 after EO shock due to the internal resistance increasing from 1.29 to 3.80 kΩ. The UOC-MFC integrated with a power management system (PMS) theoretically supported a voltage meter and data transmitter. This study well demonstrated the great potential of the UOC-MFC for in-situ detecting oil presence in a real-time self-sustained mode.
关键词： Biosensor,Upward open-channel (UOC),Self-sustainability,Oxygen diffusion on cathode,Microbial fuel cell,Oil presence monitoring
更新于2025-09-12 10:27:22
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A Novel Analysis of Transient Isothermal 18O Isotopic Exchange on Commercial CexZr1?xO2-Based OSC Materials
摘要： A novel methodology for the analysis of 18O2-transient isothermal isotopic exchange (TIIE) response curves obtained over commercial mixed metal oxides upon the gas switch 16O2/Ar (30 min) → 18O2/Kr/Ar (t) at constant T in a flow CSTR micro-reactor in the absence of external and internal mass transport resistances and grain boundary effects, is presented for the first time. The specific aim of this analysis was to derive quantitative descriptors of the 18O exchange under pseudo-equilibrium conditions for the transfer rates of oxygen between the gas and solid phases, enabling the assessment of differences in the kinetics of bulk oxygen diffusion over a series of commercial OSC materials used in various catalytic applications (e.g. TWC), without the need of performing any mathematical and kinetic modelling of the surface/bulk oxygen diffusion processes. Based on these descriptors, commercial OSC mixed metal oxides prepared by the same chemical synthesis route but varying the value of one of the synthesis parameters, and having the same at.% composition, were proved to possess largely different transient kinetic rates and other features of the transient response curves of 16O/18O exchange strongly related to the bulk oxygen diffusion in the solids. This novel 18O2-TIIE analysis is quick and provides a reliable means for proving or disproving likely infringement of patented commercial mixed metal oxides OSC materials.
关键词： OSC,Bulk oxygen diffusion,Transient isothermal oxygen isotopic exchange
更新于2025-09-04 15:30:14
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Development of a ReaxFF Reactive Force Field for Interstitial Oxygen in Germanium and Its Application to GeO <sub/>2</sub> /Ge Interfaces
摘要： We developed the ReaxFF force field parameters for Ge/O/H interactions, specifically targeted for the applications of Ge/GeO2 interfaces and O-diffusion in bulk Ge. The original training set, taken from the Zheng et al. work includes Quantum Mechanics (QM) data for equations of state and heats of formation of GeO and GeO2 condensed phases as well as dissociation energies for single and double bonds of Ge and angle distortion of O-Ge-O. We expanded this training set with the additional crystal data containing the formation energies of different O-interstitial centers and the minimum energy migration pathway of O atom in diamond Ge. After refitting the force field parameters based upon the extended training set, the ReaxFF results that the equations of state and heats of formation of the GeO and GeO2 condensed phases retain a good fit with the QM calculations. In addition, the ReaxFF correctly predicts the relative stability of the O-interstitial centers in the diamond Ge to be bond-center → split → tetrahedral → hexagonal from most stable to least stable with the energies showing quantitatively agreement with DFT. Furthermore, O atoms diffuse along a pathway between neighboring bond-centered interstitial sites and go through the asymmetric transition state at the split site as in DFT. We also examined the temperature dependence of O diffusion in bulk Ge, and subjected the GeO2/Ge interface to heat treatment based on the ReaxFF and Tersoff potential. On the basis of our MD results, the ReaxFF accurately predicts the diffusion barrier value as 50.02 kcal/mol within the temperature range of [800-2000K]. At the temperatures over 1400 K, ReaxFF allows the O atom to diffuse along the theoretically reported pathway between the adjacent BC centers whereas Tersoff potential contradicts the DFT reports by resulting a diffusion between the BC and H interstitial sites. For the Ge/GeO2 interface, the ReaxFF results that the thickness of GeO2 increases and the Ge substrate is consumed depending on the temperature and the oxidation time, supported by the experiments, while no change was observed in the thicknesses of Ge substrate and GeO2 slab in the Tersoff based simulations.
关键词： Oxygen diffusion,GeO2/Ge interface,Molecular dynamics,Germanium,ReaxFF
更新于2025-09-04 15:30:14