National Institute Of Materials Physics - Romania

We analyze the output mixed states generated when the asymmetric cloners are applied on a pure two-qubit state. We investigate two kinds of cloners: (a) local 1 -> 2 optimal universal asymmetric cloning machines and (b) nonlocal 1 -> 2 optimal universal asymmetric cloning machines. In both cases we find analytical formulae of the geometric quantum discord of the two clones. Finally, we prove that the geometric quantum discord generated by the nonlocal asymmetric cloners is not smaller than the geometric quantum discord given by the local asymmetric cloners.

Lithium borohydride (LiBH4) is a promising hydrogen storage material releasing 13.8 wt% H2 upon decomposition in lithium hydride and boron, significantly surpassing other complex hydrides. However, sluggish dehydrogenation kinetics still hinder the use for practical applications. The infiltration of LiBH4 into carbon nanoscaffolds has proved to be effective in improving the hydrogen absorption/desorption (a/d) kinetics. Further improvement of storage kinetics can be achieved by modification of the nanocarbon with dopant elements. The present work compares nanoporous carbon (C-MSU-H) and C-MSU-H doped either with 1 at% N or 1 at% Ni as the matrix for infiltration of LiBH4. The catalytic effect of nitrogen proved to be superior to that of nickel (keeping the same doping level) for improving the hydrogen a/d kinetics of LiBH4 infiltrated in doped C-MSU-H. X-ray photoelectron spectroscopy was used to detect the amount and chemical proximity of nitrogen in nanoporous carbon following the thermal treatment in ammonia flow. The morphology and porosity of doped C-MSU-H were investigated by X-ray diffraction, FTIR, TEM, and BET. Hydrogen a/d kinetics of LiBH4@C-MSU-H nanocomposites was investigated by a volumetric method. The desorption peak temperatures (measured at 2 degrees C min-1 rate) are 339 degrees C for the undoped LiBH4@C-MSU-H, 328 degrees C for the LiBH4@C-MSU-H doped with 1 at% Ni and 318 degrees C for the LiBH4@C-MSU-H doped with 1 at% N nanocomposites. The activation energies of hydrogen desorption for the investigated nanocomposites were obtained from Kissinger plots: 142.7 kJ mol-1 for undoped LiBH4@C-MSU-H, 123.8 kJ mol-1 for LiBH4@C-MSU-H 1 at% Ni and 119.5 kJ mol-1 for LiBH4@C-MSU-H 1 at% N nanocomposites. The catalytic effect on LiBH4 dehydrogenation due to N-doping of nanocarbons is discussed.

Zinc oxide (ZnO) and zinc sulfide (ZnS) nanocomposites represent promising multifunctional photocatalysts due to their complementary band structures and synergistic charge separation. ZnO-ZnS nanocomposites with varied ZnS content were synthesized to elucidate the composition-structure-property relationships governing their multifunctional performance. Structural characterization using XRD, SEM/EDS, Raman spectroscopy, and XPS confirmed the coexistence of wurtzite crystalline phases of ZnO and ZnS. SEM analysis revealed ZnS fine deposition on the ZnO surface. XPS measurements showed a gradual increase in the amount of ZnS on the ZnO surface with increasing sulfide content and a shift in the valence band maximum from 2.32 eV (pure ZnO) to 0.77 eV (pure ZnS). Optical measurements (IR, UV-Vis diffuse reflectance, photoluminescence) demonstrated that, despite the evolution of vibrational and luminescence features characteristic of ZnS, the apparent band gap remained nearly constant at 3.16-3.18 eV across the series. Photocatalytic methylene blue (MB) degradation followed pseudo-first-order kinetics, peaking for ZN_2 (1% ZnS, kapp = 103 & times; 10-3 min-1), which is 1.7 times higher than for pure ZnO. This enhanced performance is consistent with an S-scheme-like heterojunction that facilitates electron migration to the ZnS conduction band while retaining ZnO valence band holes for oxidation. Scavenging experiments confirmed that electrons dominate MB degradation (kapp up to 185.1 & times; 10-3 min-1 with EDTA/t-BuOH/Ar), outperforming hole-mediated pathways. Antibacterial assays against Staphylococcus aureus revealed good antimicrobial activity for all nanoparticles. The nanocomposite's antibacterial activity was similar across all samples and was only slightly lower than that of pure ZnS and ZnO.

This study presents the development and analysis of a highly sensitive SnO2-based gas sensor for acetone detection, enhanced through the wet impregnation with WO3. Structural and morphological investigations confirm the tetragonal structure of the SnO2 crystalline phase and reveal irregular grain boundaries that become less pronounced with increasing WO3 content. Surface chemistry analyses confirm the presence of well-dispersed WO3 on the SnO2 surface. Thick and porous sensing layers were fabricated by screen printing onto commercial alumina substrates. The influence of operating temperature on surface interactions was evaluated by measuring the sensor response at a fixed acetone concentration. This enabled the selection of SnO2:WO3 5 % for sensing measurements, at an operating temperature of 280 degrees C, over a wide range of acetone concentrations, dosed in dynamic airflow with variable relative humidity. Simultaneous DC electrical resistance and Contact Potential Difference measurements allow decoupling of ionosorption from dipolar effects on the SnO2:WO3 5 % surface and explain the rise in the sensor response to acetone as relative humidity increases. The chosen concentration range for acetone, between 0.25 and 5 ppm, and for relative humidity, between 10 and 90 %, creates the premises for the further development of applications for non-invasive monitoring of diabetic exhalation.

Conversion of hazardous vanadium spent catalysts (VSCs) to high added value vanadium-based materials is an effective solution for environmental remediation as well as cost-effective energy storage applications. In the present work, we introduce a new green hydrometallurgical process based on a novel synergistic sulfuric acid-hydrazine monohydrate (H2SO4-N2H4 & centerdot;H2O) leaching system, achieving a high vanadium extraction of 97.8%. The purified vanadyl sulfate solution (99.96%) of the subsequent solvent extraction was converted into V2O5 and utilized for the production of Na3V2(PO4)2F3@C (NVPF@C) cathode material via a solid-state approach for SIB application. The NVPF@C electrodes exhibited an interesting electrochemical performance, delivering 115 mAh g-1 at 0.2C and retaining 89% capacity after 100 cycles at 1C, with remarkable rate capability. Economic and environmental assessment indicated savings of 72.9% in vanadium pentoxide cost as well as a range of 68.6-96.7% in greenhouse gas emission reduction compared with conventional leaching systems. This study highlights the feasibility of closing the loop for vanadium resources, offering a scalable and environmentally friendly route to battery-grade precursors. The approach not only validates the use of recycled vanadium in high-performance sodium-ion batteries but also emphasizes the integration of circular economy principles and sustainable practices in next-generation energy storage technologies.

Magnesium and zinc are important additives or substituents in melt-quenched Na2O-CaO-SiO2-P2O5 bioactive glasses, due to their beneficial influence on glass stability and processability. They modify the dissolution kinetics of these glasses and impart favorable biological properties and functions to them. For rational bioactive glass design, it is essential to understand the local environments and distributions of these ions. While diffraction studies suggest MgO and ZnO to be close-to-four-coordinate in silicate glasses, their structural roles in the network are still under debate. Traditionally these oxides have been viewed as network modifiers, converting Si-O-Si linkages to anionic non-bridging oxygen atoms, whose charges are compensated by the divalent cations. It has been suggested that MgO4/2|(2-) or ZnO4/2|(2-) network-forming units (NFUs) may be present, forming Mg-O-Si or Zn-O-Si linkages. If such units are formed, they would attract modifier cations for charge compensation, which would in turn result in an increased degree of polymerization of the silicate species, the main network-forming component. This study explores the roles of MgO and ZnO in bioactive glasses with approximate composition 50SiO(2)-(50-x)[MO,M'O-2]-xP(2)O(5) in mol% (2 <= x <= 6), where M = Ca, Sr, Mg, Zn; M' = Na, K. Quantitative estimates of the various silicate and phosphate NFUs were obtained from Si-29 and P-31 solid-state nuclear magnetic resonance (NMR) spectroscopic techniques and molecular dynamics (MD) simulations, allowing the determination of the degree of network polymerization in terms of the average Si and P connectivities (-values). Both NMR spectroscopy and MD studies consistently revealed that the extent of Si polymerization increases, as expected, with P2O5 addition, reflecting the well-documented preferential cation attraction by the phosphate species. On the other hand, data obtained from a set of comparative samples containing either Mg, Zn, or a mixture of both showed no significant changes in the degree of silicate network polymerization. This result strongly supports a network-modifying role of both magnesium and zinc oxide, as suggested by previous works.

This paper reports a method for separating the constituents of a cathode containing a composite of the type polydiphenylamine (PDPA)/multi-walled carbon nanotube grafted with carboxyl groups (PDPA/MWCNT-COOH-1) as active material in end-of-life rechargeable lithium-ion batteries (RLIB) and their reuse as active materials in the field of other energy storage devices. The materials recovered from lithium battery cathodes are characterized by FTIR spectroscopy, Raman scattering, surface-enhanced Raman scattering (SERS), and X-ray diffraction. The use of the PDPA/MWCNT-COOH-1 composite as active material in the development of new energy storage devices, such as symmetric supercapacitors, is also reported. The performance comparison of the recycled composite material (PDPA/MWCNT-COOH-1 and MWCNT-COOH) with the one synthesized from pure chemical compounds (PDPA/MWCNT-COOH-2) is shown. Values of the capacitance of symmetrical supercapacitors, having as electrode materials the composites of the type of a mixture of PDPA/MWCNT-COOH-1 and MWCNT-COOH, as well as PDPA/MWCNT-COOH-2, are equal to 136.6 mF cm-2 and 112.59 mF cm-2. Increasing the concentration of the PDPA/MWCNT-COOH-2 active material in the electrode mass from 80 wt% to 84 wt% led to variations in the capacitance values of the symmetrical supercapacitors from 112.59 mF cm-2 to 145.5 mF cm-2.

HfZrO2(HZO) is a promising ferroelectric material compatible with CMOS technology, retaining functionality at nanometer-scale thicknesses. Its ferroelectricity arises from metastable polar phases-orthorhombic (Pca21) and rhombohedral (R3m)-coexisting with the thermodynamically stable, non-polar monoclinic phase (P21/c). Accurate quantification of these coexisting phases is essential for optimizing device performance. Here, we use first-principles calculations to estimate core-level shifts in the O 1s X-ray photoelectron spectroscopy (XPS) peak, revealing a distinct, up to 0.84 eV higher binding energy component for oxygen atoms in the polar sublattice compared to those in non-polar environments. These shifts incorporate both initial and final state effects in photoemission. Experimental validation through X-ray diffraction (XRD) and XPS on HZO films with varying phase composition confirms our predictions. Our findings provide a clear, spectroscopically accessible fingerprint to distinguish polar and non-polar phases in HZO via O 1s XPS analysis, offering a practical tool for phase quantification and enabling targeted integration of ferroelectricity in advanced nanoelectronic devices.

A new mechanism is proposed for polarization switching in metal-ferroelectric-metal (MFM) structures. The switching is triggered by charge injection at electrode or grain interfaces under an external field, opposite to the initial direction of polarization. Such injection destabilizes the compensation of the polarization, and is favored by disappearance of Schottky barriers at interfaces, leading to a resistive like behavior. At the coercive voltage the depolarization field is no longer compensated and the polarization change orientation parallel to the applied field. After switching, the Schottky barriers are restored and the current start to decrease although the voltage continues to increase. This leads to a differential negative resistance until the barriers are totally restored, polarization saturated on the new direction and the depolarization field annihilated by the injected charges. In a perfect structure the switching takes place homogeneously, while the defects presence induces domains via local nucleation and fields. The model is supported by theory, showing that at switching the MFM structure has a resistive like behavior, and by experiments, showing that the voltage dependence of the current during switching is linear and that the phase change at switching, in PFM measurements performed on high quality epitaxial films, is abrupt. The analysis was performed on MFM structures based on different ferroelectric layers (e.g. Pb(Zr,Ti)O3, BaTiO3, BiFeO3 or (HfZr)O2), different metal electrodes and different structural qualities. It appears that polarization switching triggered by charge injection at interfaces is a mechanism that can be applied to all MFM structures based on oxide ferroelectrics.

Since 2016, a peculiar trend in the synthesis of layered double hydroxide solids involves the use of organic alkalis, e.g., quaternary ammonium hydroxides that play the role of a synthesis agent as well as a template molecule. This approach adapts the tailored textural properties of the final solid, also eliminating the occurrence of disadvantages due to the use of inorganic alkalis in the synthesis process of LDH-type solids (e.g. possibility of contamination with alkali metals, high energy consumption, significant waste production, etc.). However, the attempt to insert the copper cation into the octahedral positions of LDH using the organic alkali (i.e. tetramethylammonium hydroxide) leads to the obtaining of a layered structure contaminated with Cu(OH)2. The nature of the precursor used for LDH synthesis plays a particular role because, for example, the use of sulfates leads to ill crystallized structures due to their lower reactivity. Regardless of the synthesis method used (co-precipitation as a traditional method or mechanochemical as a non-traditional one) and the nature of the precursors involved (nitrates, chlorides, sulfates) in the synthesis process, copper was not completely inserted into the octahedral positions for the molar ratio of divalent cations considered, i.e. Cu/Mg=1. The use of tetramethylammonium hydroxide as a synthesis agent also generates tailored textures where the surface areas were in the range of 0.9 and 19.5 m2 & sdot;g-1. The electronegativity values of the cations involved, e.g. Mg, Cu and Al, played an essential role in determining the basicity values. Both the basicity and the catalytic activities kept a linear variation trend in the Claisen-Schmidt condensation between benzaldehyde and cyclohexanone. The low basicity and the presence of acid sites due in particular to the presence of the Cu cation in the solid structure, a fact perceived as a disadvantage in base-catalyzed reactions, actually represented the key to the selectivity of the transformation into the mono-condensed product (2-benzylidenecyclohexanone). In accordance with this trend, the amount of the thermodynamically favored product, i.e. 2,6-dibenzylidenecyclohexanone (di-condensed product), decreases. The highest cyclohexanone conversion of 88.4 % was presented by D-NO3--MC (with 97.3 % as selectivity to di-condensed product). A similar result was obtained for Hy-NO3--CP. Meanwhile, C-SO42--CP generated 46.3 % conversion of benzaldehyde to benzoic acid in a side reaction. The catalysts obtained from nitrate precursors, allowed reaching higher conversions of cyclohexanone with enhanced selectivity for the di-condensed product. After 3 reaction cycles, especially Al and Cu were extracted from the octahedral positions leading to the formation of side phases, e.g. hydroxides, carbonates, hydroxycarbonates, but also dypingite like phase.