Ultrathin Magnesium-based Coating as an Efficient Oxygen Barrier for Superconducting Circuit Materials

Scaling up superconducting quantum circuits based on transmon qubits necessitates substantial enhancements in qubit coherence time. Among the materials considered for transmon qubits, tantalum (Ta) has emerged as a promising candidate, surpassing conventional counterparts in terms of coherence time. However, the presence of an amorphous surface Ta oxide layer introduces dielectric loss, ultimately placing a limit on the coherence time. In this study, we present a novel approach for suppressing the formation of tantalum oxide using an ultrathin magnesium (Mg) capping layer deposited on top of tantalum. Synchrotron-based X-ray photoelectron spectroscopy (XPS) studies demonstrate that oxide is confined to an extremely thin region directly beneath the Mg/Ta interface. Additionally, we demonstrate that the superconducting properties of thin Ta films are improved following the Mg capping, exhibiting sharper and higher-temperature transitions to superconductive and magnetically ordered states. Based on the experimental data and computational modeling, we establish an atomic-scale mechanistic understanding of the role of the capping layer in protecting Ta from oxidation. This work provides valuable insights into the formation mechanism and functionality of surface tantalum oxide, as well as a new materials design principle with the potential to reduce dielectric loss in superconducting quantum materials. Ultimately, our findings pave the way for the realization of large-scale, high-performance quantum computing systems

Rietveld Refinement and X-ray Absorption Study on the Bonding States of Lanthanum-Based Perovskite-Type Oxides La_1−<i>x</i>Ce<i>_x</i>CoO₃

Metal-oxygen bonding of the Ce-doped LaCoO3 system remains largely unexplored despite extensive studies on its magnetic properties. Here, we investigate the structure and local structure of nanoscale La1−xCexCoO3, with x = 0, 0.2, and 0.4, using the Rietveld refinement and synchrotron X-ray absorption techniques, complemented by topological analysis of experimental electron density and electron energy distribution. The Rietveld refinement results show that LaCoO3 subject to Ce addition is best interpretable by a model of cubic symmetry in contrast to the pristine LaCoO3, conventionally described by either a monoclinic model or a rhombohedral model. Ce4+/Co2+ are more evidently compatible dopants than Ce3+ for insertion into the main lattice. X-ray absorption data evidence the partially filled La 5d-band of the pristine LaCoO3 in accordance with the presence of La–O bonds with the shared-type atomic interaction. With increasing x, the increased Ce spectroscopic valence and enhanced La–O ionic bonding are noticeable. Characterization of the local structures around Co species also provides evidence to support the findings of the Rietveld refinement analysis

Boosting Cathodic Performance of Ni-rich NCM811 via Uric Acid Derived Nitrogen-doped Carbon-Coating in Lithium-Ion Batteries

The nickel-rich layered Li[Ni0.8Co0.1Mn0.1]O2, popularly known as NCM811, is considered a high-performance cathode material in lithium-ion batteries (LIBs) due to its high specific capacity and energy density. However, because of its poor structural stability, it suffers from long-run performance in LIBs. The surface coating technique can enhance the performance of the NCM811 cathode by preventing its surface degradation during prolonged contact with electrolytes. Herein, we report a uric acid-derived nitrogen-doped carbon-coated NCM811 cathode to enhance the cathodic performance. The materials were prepared by a facile one-step calcination in which different weights of uric acid are mixed well with NCM811 through ball milling followed by sintering. The XRD peaks confirm the formation of a pure phase in both the bare and modified NCM811 materials. The morphological characteristics and coating thickness are observed by FE-SEM and FE-TEM analysis, respectively. Electrochemical characterizations such as galvanostatic charge-discharge (GCD), cyclic performance, and rate capability studies show that the 0.1-NCM811 material can effectively tailor the electrochemical performance of the cathode in LIBs. The capacity retention of 0.1-NCM811 material is 92.7% and 85.8% at 100 cycles in 0.1C and 300 cycles in 1C, respectively. The improved electrochemical performance of coated NCM811 cathode is associated with the effective coating of nitrogen-doped carbon which can hinder the electrode dissolution process while amplifying the ionic conductivity

Novel photocatalytic coating for corrosion mitigation in 304LSS of dry storage canisters

Type 304L stainless steel (304LSS) is one of the candidate canister materials for storing radioactive spent fuels, usually near seashore environments along with nuclear power plants. During the prolonged exposure of dry storage canisters to saline environments, they are highly susceptible to chloride induced stress corrosion cracking. Failure of a dry storage canister not only would release radioactive isotopes into the environment, but would also lead to a costly replacement of the cracked canister. The objective of this study is to develop a multilayered titanium dioxide (TiO2) composite coating on a 304LSS substrate. With ultraviolet (UV) illumination, this coating would act as a barrier and simultaneously offer cathodic protection against corrosion in the substrate alloy. The composite coating consists of a plain amorphous TiO2 coating over another cerium-doped (Ce-doped) TiO2 coating. Electronic currents generated by photo-catalytic reaction of the amorphous TiO2 coating under UV illumination were measured. Photo-electrochemical analyses and surface morphology observations were conducted to evaluate the performance of the Ce-doped coatings on corrosion mitigation. Optimal amounts of cerium doping that offered better photo-cathodic protection were also explored. Results indicated that the Ce-doped TiO2 coating exhibited a better performance on photo-cathodic protection for 304L stainless steel in aerated 3.5% NaCl solutions than the one without cerium doping. The underlying Ce-doped TiO2 coating was effectively charged during UV illumination, and it was able to continuously release electrons even after the UV was switched off, thus providing uninterrupted photo-cathodic protection for the coated 304L stainless steel substrate