Search Results (1,299)

To address the inherent drawbacks of micro-arc oxidation (MAO), this study employed MAO combined with sol–gel processing to fabricate ZrO₂/Al₂O₃-CeO₂ composite coatings on ZrH_1.8 surfaces, aiming to solve the hydrogen evolution problem of zirconium hydride (ZrH_1.8) materials in high-temperature environments. By adjusting the aluminum concentration in the sol (0.1~0.5 mol/L), a series of composite thin films were prepared on the ZrH_1.8 surface using MAO combined with dip-coating, and their surface morphology and phase composition were characterized. The microstructure, morphology, and hydrogen barrier performance of the thin films were systematically analyzed using scanning electron microscopy (SEM), XRD, laser confocal microscopy, and quadrupole mass spectrometry. The results showed that the composite coating had a low surface porosity, with a maximum hydrogen permeation reduction factor (PRF) of 18.1. When the aluminum concentration was 0.4 mol/L, the relative content of tetragonal ZrO₂ (T-ZrO₂) reached 13.88%, the surface porosity was as low as 4.87%, and the initial temperature of hydrogen loss was increased to 730 °C. Mechanism analysis indicated that CeO₂ may stabilize the tetragonal phase (T-ZrO₂) of ZrO₂ through solid solution effects and inhibit the phase transformation to monoclinic phase (M-ZrO₂), thereby reducing cracks caused by volume expansion. Meanwhile, the synergistic effect of the MAO densified layer and the sol–gel sealed porous layer significantly reduced the coating porosity and blocked hydrogen diffusion paths, thus achieving excellent hydrogen barrier performance under high-temperature conditions. Full article

An efficient catalyst for the reaction of ethanol–acetaldehyde into 1,3-butadiene (EATB) is prepared through the grafting of zirconia into a zeolite Beta lattice. The grafting is achieved through the dealumination of a zeolite framework by acid treatment followed by zirconia impregnation, leading to the substitution of aluminum in the zeolite framework by zirconia. The catalyst with zirconia grafted into the zeolite framework promotes desirable catalyst properties like high zirconium dispersion, stability, and the close proximity of Lewis acid, Bronsted acid, and medium basic sites. The phase, the coordination of zirconia, the location of the active center and the cooperative synergism were elucidated through various characterization techniques, including X-ray diffraction, Raman spectroscopy, N₂ adsorption, UV–vis spectroscopy, XPS, ²⁹Si MAS NMR, NH₃-TPD, Py-IR, CO-IR and CO₂-TPD. The catalytic results show that a suitable phase and content of zirconia were needed to improve the ethanol–acetaldehyde conversion, butadiene selectivity and catalyst stability. Among the catalysts, m+t-ZrO_x-Beta-H₂O-9020 (m = monoclinic, t = tetragonal ZrO₂ phase) achieved the best butadiene selectivity of 82–73% at the conversion of 100–66%, run over 200 h. The results allow us to propose a Lewis acid–medium basic pairing for the Si–O–Zr–O–Si group, where the adjacent Si-OH is the active center for reactions. Full article

Zirconia-toughened alumina (ZTA) ceramics are promising for load-bearing biomedical applications because they combine the hardness, chemical stability, wear resistance, and biocompatibility of alumina with the transformation-toughening capability of zirconia. Grinding is indispensable for achieving dimensional accuracy and surface quality, yet it inevitably introduces surface and subsurface cracks, residual stresses, and a local tetragonal-to-monoclinic transformation of zirconia. These changes can degrade fracture toughness, increase reliability scatter, and reduce long-term service stability. Annealing is therefore often considered a post-grinding recovery strategy because it can relax residual stresses, blunt crack tips, and partially restore the zirconia phase state. However, the extent of recovery depends strongly on the initial damage state, ZTA microstructure, and thermal schedule. This review systematically summarizes the current understanding of grinding-induced damage and annealing-assisted recovery in ZTA ceramics, with particular emphasis on the coupled relationships among subsurface damage, residual-stress evolution, phase transformation, and fracture toughness. Particular attention is given to distinguishing direct ZTA-specific evidence from mechanistic interpretations inferred from related zirconia-containing ceramic systems, because datasets based exclusively on ZTA remain relatively limited. By integrating the existing evidence, this review proposes a coupled processing-damage-recovery framework and identifies the key knowledge gaps that must be addressed to achieve more reliable process optimization in advanced ZTA components. Full article

Bismuth oxide (Bi₂O₃) nanoparticles are attractive for biomedical and radiation-shielding technologies and can be further tailored through the addition of other metal oxides to address emerging needs such as antimicrobial resistance. This study investigated the effects of incorporating Fe₂O₃ and La₂O₃ on the structure, morphology, and antimicrobial performance of Bi₂O₃-based nanocomposites synthesized via a plant extract-assisted microwave–hydrothermal route using soapnut extract. XRD indicated that pure Bi₂O₃ (100B) comprised predominantly monoclinic α-Bi₂O₃ with coexisting metastable tetragonal β-Bi₂O₃. The addition of Fe (3F; Fe:Bi = 30:70) promoted β- Bi₂O₃ and formed BiFeO₃, while increasing La substitution (3L–20L) reduced the BiFeO₃ intensity and, beyond a threshold (≥7L), yielded distinct La₂O₃ peaks consistent with a La₂O₃–BiFeO₃–Bi₂O₃ composite. Crystallite size decreased from ~46 nm (100B) to ~25 nm (3F), varying with La between 33 and 25 nm. SEM/TEM revealed a reflection in morphology and size with composition from disk-like particles to petal-like spherical aggregates. Antimicrobial screening revealed composition-dependent inhibition: against S. aureus, 20L was the most potent (~94%). Overall, La/Fe tuning under a plant extract-assisted microwave–hydrothermal route enabled phase- and morphology-controlled Bi₂O₃-based nanocomposites with enhanced antimicrobial activity, with ultrafine, high-surface-area architectures emerging as promising antibacterial candidates. Full article

Y₂SiO₅ (YSO) and Lu₂SiO₅ (LSO) are orthosilicates used in photonic and scintillation applications. Isovalent substitution on the rare-earth sublattice in YSO–LSO solid solutions enables systematic tuning of lattice parameters and elastic properties without changing the underlying monoclinic structural framework. A systematic ab initio study of structural, elastic, and vibrational properties of Ce-free YSO–LSO solid solutions is performed within density functional theory using a localized Gaussian-type orbital basis. Nine compositions spanning the full range from YSO to LSO with a Lu content step of 12.5% are investigated. A total of 76 symmetry-independent Y/Lu substitution patterns are explicitly constructed. For each configuration, full geometry optimization and calculation of second-order elastic constants are carried out using the stress–strain approach. Bulk, shear, and Young’s moduli, as well as Poisson’s ratio, are obtained using the Voigt, Reuss, and Hill averaging schemes. Sound velocities and Debye temperatures are derived from the Hill-averaged elastic moduli and density. The unit-cell volumes decrease smoothly with increasing Lu content and follow Vegard’s law, indicating uniform lattice contraction. The Hill-averaged bulk modulus increases from 92 GPa (YSO) to 115 GPa (LSO), the Young’s modulus rises from 151 to 180 GPa, and a strong directional anisotropy (ratio ∼2) is preserved across the entire series. The Debye temperature decreases monotonically from 518 K to 439 K, indicating that the increase in mass density outweighs the stiffening-induced tendency toward higher sound velocities. These results provide quantitative guidance for composition selection and stress management in LYSO-based crystal detectors. Full article

This paper reports the controlled synthesis of ZrO₂ nanocrystals via a peroxide-assisted hydrothermal (HT) route at 120 °C, with processing times ranging from 12 to 72 h, and investigates the correlation between structural evolution, defect chemistry, and functional properties. X-ray diffraction (XRD) combined with Rietveld refinement confirmed the formation of a monophasic monoclinic structure with high structural reliability. Microstructural analysis revealed progressive crystallite growth and lattice ordering with increasing reaction time, accompanied by subtle distortions in local coordination environments. Micro-Raman spectroscopy indicated improved medium-range structural organization at longer synthesis durations, while transmission electron microscopy showed quasi-spherical and nanorod-like aggregates formed through oriented attachment, with particle sizes of 6–9 nm. Optical investigations using diffuse reflectance spectroscopy revealed band gap energies of 3.45–3.65 eV, attributed to defect-induced intermediate electronic states associated primarily with oxygen vacancies. A comprehensive photoluminescence (PL) analysis suggests that the observed emission arises from defect-mediated recombination pathways involving localized states within the band gap, modulated by the interplay between structural order and residual defects. The role of hydrogen peroxide is discussed in terms of regulating oxygen vacancy concentration, promoting structural stabilization while preserving functional defect states. The results demonstrate that precise control of HT processing time enables tuning of structural disorder, defect density, optical response, and the enhanced photocatalytic performance of ZrO₂ toward RhB dye degradation, highlighting its potential for optoelectronic applications. Full article

Lithium-ion batteries require cathode materials with high capacity and cycling stability. Li₃V₂(PO₄)₃ (LVP) offers a theoretical capacity of 197 mAh/g but suffers from poor electronic conductivity. In this study, a Li₃V₂(PO₄)₃/carbon (LVP/C) composite was synthesized via a citric acid-assisted sol–gel method. The effects of pyrolysis temperature (700–1000 °C) and citric acid-to-salt ratio (1:1, 0.5:1, 0.25:1) were systematically investigated. The optimal composite was obtained at 900 °C with a 1:1 ratio. This material exhibited a well-crystallized monoclinic structure (space group P2₁/c) with unit cell volume of 890.61 ų. The amorphous carbon coating provided a specific surface area of 33.03 m²/g. Electrochemically, the optimal LVP/C_1:1 composite delivered an initial specific capacity of 114 mAh/g at C/10 rate—twice that of samples with lower carbon content. It also demonstrated 100% capacity retention after 25 cycles with favorable coulombic efficiency (67%) and reduced charge-transfer resistance. These results show that pyrolysis at 900 °C with a 1:1 citric acid-to-salt ratio provides an optimal balance between crystallinity, carbon coating uniformity, and electrochemical performance for high-performance LVP/C composite cathodes. Full article

This study investigates the phase composition and vibrational characteristics of a powder metallurgy-processed Ti–6Al–4V alloy reinforced with ZrO₂. Raman spectroscopy confirmed that the ZrO₂ powder predominantly exhibits a monoclinic structure, while the Ti–6Al–4V alloy contains anatase and rutile TiO₂, along with minor Ti₃O₅ phases. Optical microscopy revealed a well-defined grain structure on the Ti–6Al–4V/ZrO₂ composite surface, which was subsequently examined in greater detail using Raman imaging combined with True Component analysis. The spatially resolved Raman maps demonstrated that the visually distinct light and dark grains possess a similar chemical composition, consisting mainly of ZrO₂ and TiO₂ phases. This represents the first application of Raman imaging to Ti–6Al–4V/ZrO₂ composites, offering new insight into the relationship between microstructure and phase distribution in this material system. Full article

Yttrium doping has been reported to be an effective approach to enhance the mechanical and protective properties of ZrN coatings by magnetron sputtering. Nitrogen (N₂) flow ratio during reactive magnetron sputtering is known to critically influence the stoichiometry, defect structure, and microstructure of nitride coatings. However, its systematic effect on Y-doped ZrN (ZrYN) coatings has remained unexplored. In this work, ZrYN coatings with a fixed Y content were deposited by reactive magnetron sputtering under varying N₂ flow ratios (0–10%). Their microstructure, mechanical properties, corrosion resistance in 3.5 wt% NaCl solution, and oxidation behavior at 650 °C were systematically investigated. Below 5% N₂ flow ratio, the coatings are metallic ZrY, showing very low hardness, poor corrosion resistance, and catastrophic oxidation failure. At N₂ flow ratio ≥ 5%, cubic ZrYN forms, with stoichiometry varying from sub-stoichiometric (5%) to near-stoichiometric (7.5%) to over-stoichiometric (10%). The near-stoichiometric coating at 7.5% exhibits the finest columnar grains and densest microstructure, leading to the highest hardness (32.2 ± 1.4 GPa) and an elastic modulus of (469.6 ± 24.5 GPa), as well as the best corrosion resistance (two orders of magnitude lower than bare 316 stainless steel). Upon oxidation, it forms a thin and dense epitaxial t-ZrO₂ scale stabilized by Y₂O₃, suppressing the destructive tetragonal to monoclinic transformation. Off-stoichiometric coatings at 5% and 10% develop thicker, cracked oxide scales and show inferior properties. Precise control of N₂ flow ratio is therefore essential to achieve a near-stoichiometric ZrYN coating with superior mechanical, anti-corrosion, and anti-oxidation performance. Full article

In most cases, columbite-supergroup minerals are characterized by partial ordering of cations, which makes their identification based only on chemical composition and powder diffraction data difficult. Columbite-supergroup minerals with partially ordered cations were studied by means of electron microprobe analyses, powder and single-crystal X-ray diffraction, including crystal structure refinement in ixiolite-type and wolframine-type models. The samples originate from the Sakhanaiskiy granite massif, Eastern Siberia, Russia, (Sample 1) and from the Heftetjern pegmatite, Telemark, Norway (Sample 2). Their representative empirical formulae are (Fe²⁺_0.81Mn²⁺_0.53)_Σ1.34Fe³⁺_0.07(Ti_0.23Zr_0.11Sn_0.02)_Σ0.36(Nb_1.45Ta_0.26)_Σ1.71W_0.52O₈ (Sample 1) and (Mn²⁺_0.28Fe²⁺_0.25)_Σ0.53Sc_1.08(Sn_0.32Ti_0.04)_Σ0.36(Ta_1.41Nb_0.52)_Σ1.93W_0.10O₈ (Sample 2). Based on these data and the results of the crystal structure refinement, the studied samples can be considered as columbite-supergroup minerals in which cations are partially ordered in accordance with the wolframite mechanism. An approach is suggested according to which the degree of cation ordering in such columbite-supergroup minerals can be estimated based on the electron contents refined for different sites in a monoclinic model. According to this criterion, the degree of cation ordering of Samples 1 and 2 is 91% and 26%, respectively. Despite a significant degree of cation disordering, transition from the wolframite to ixiolite model results in a significant enhancement of the R-factor of the structure refinement (from 0.0365 to 0.0764 and from 0.0207 to 0.0610, respectively). Full article

In this study, fully bio-based oligomers of butylene succinate (OBS) with different molecular weights (low: L-OBS, medium: M-OBS and high: H-OBS) were incorporated into poly(butylene succinate) (PBS) by melt mixing at varying loadings of 5–15 wt%. Then, PBS/OBS films were obtained by thermo-compression and characterized to assess their suitability for sustainable food packaging. Thus, OBS were homogeneously incorporated into PBS matrix and modulated the thermal, mechanical, and barrier properties of the PBS. L-OBS (Mn = 1150 g·mol⁻¹) plasticized the amorphous PBS, depending on its concentration, more effectively than M-OBS (Mn: 8700 g·mol⁻¹) and H-OBS (Mn: 18,650 g·mol⁻¹), as deduced from the thermo-mechanical analysis. In every case, OBS enhanced crystallinity, mainly L-OBS, which reduced the film strength and increased water vapor permeability, depending on its concentration. In contrast, H-OBS improved mechanical strength, stiffness, and barrier performance. In all cases, X-ray diffraction confirmed the preservation of the PBS’s monoclinic crystalline structure but slightly shifted the diffraction angle depending on the ratio of the end-chain groups in the blend, thus reflecting the contribution of OBS in the crystalline lattice. Finally, oligomer incorporation resulted in an overall migration increase in different food simulants, impairing their application in packaging. Full article

The stability of the competing orthorhombic Pnma and monoclinic P2₁/c phases of Praseodymium pentaphosphate (PrP₅O₁₄) have been studied using density functional theory (DFT). At 0 K, the Pnma structure is found to be preferred over the P2₁/c one with the enthalpy change with pressure of both phases highlighting a shift in phase preference from Pnma to P2₁/c at ∼2.5 GPa. Independently of the predicted high-pressure structural phase transition at 0 K, our computed elastic properties and phonon dispersion bands as a function of pressure indicate a phonon instability at ∼4.5 GPa due to the appearance of imaginary frequencies, followed by a dynamical instability at 8.5 GPa due to the violation of the Born criteria on the Pnma structure of PrP₅O₁₄. These results eliminate the orthorhombic structure as a possible high-pressure candidate for the monoclinic P2₁/c polymorph. Furthermore, the relative stability of the orthorhombic and monoclinic polymorphs has been evaluated at ambient pressure and as a function of temperature by means of vibrational free-energy calculations. The results indicate a free-energy crossing at 42 K, with the Pnma phase being energetically favored from 0 K to 42 K, after which the P2₁/c phase becomes preferred. These results demonstrate why PrP₅O₁₄ can only be obtained at ambient pressure in the monoclicnic P2₁/c polymorph, different to other rare earth pentaphosphates. Full article

Fully dense monoclinic zirconia ceramics were successfully fabricated by pressureless sintering and/or HIP. Although monoclinic zirconia exhibits unique physicochemical properties, fabrication of fully dense polycrystalline bodies has remained challenging due to catastrophic volume expansion during the tetragonal-to-monoclinic transformation. By introducing a synergistic ternary (Ga₂O₃-ZnO-TiO₂) sintering aid, a relative density exceeding 99.6% with an average grain size of 0.5–2 µm was achieved by sintering under an oxygen atmosphere at 1070 °C for 3–100 h, well below the phase-transition temperature. X-ray diffractometry confirmed a single-phase monoclinic structure. Subsequent hot isostatic pressing at 1080 °C and 180 MPa for 2 h eliminated residual porosity, yielding a 4-point bending strength of 328 MPa, a fracture toughness of 2.7 MPa·m^0.5, and a Vickers hardness HV₁ of 805. This monoclinic zirconia ceramic exhibited ~30% total transmittance, while in-line transmittance remained below 0.1% due to intrinsic birefringence of the monoclinic lattice. These results established a low-temperature route for densifying phase-sensitive ceramics while achieving long-term stability. Full article

The crystal structures of monoclinic paracetamol, its cocrystal with oxalic acid (ParaOA), and its HCl monohydrate salt (ParaHCl) were refined by density functional theory (DFT) calculations and contrasted with the initial X-ray diffraction (XRD) structures. Two independent, but largely consistent, assessments were made: (i) comparisons between ¹H and ¹³C chemical shifts obtained from magic-angle spinning (MAS) nuclear magnetic resonance (NMR) experiments and those predicted by plane-wave DFT calculations before and after geometry optimization; (ii) direct ¹H–¹H distance evaluations by a recently introduced NMR crystallography method that offers straightforward structure assessments due to interatomic-distance constraints from one double-quantum–single-quantum (2Q–1Q) ¹H NMR correlation experiment. For both the ¹H/¹³C chemical shift and ¹H–¹H distance assessments, the geometry-optimized ParaHCl structure offered a markedly better match than the initial XRD structure, while the XRD structure of paracetamol revealed excellent agreement with the NMR data, with only marginal improvements offered by the DFT optimization. The XRD-derived structure of ParaOA also agreed well with the NMR chemical shift/distance constraints: While the computed ¹³C chemical shifts showed better agreement with those from MAS NMR, slightly larger discrepancies were observed for the ¹H chemical shifts and the ¹H–¹H distances. We also discuss the chemical shifts and present the first ¹H and ¹³C MAS NMR-peak assignments for the ParaHCl and ParaOA structures. Full article

K-ion batteries (KIB) are considered the future energy storage and conversion technology due to their remarkable performance. In this work, a high-temperature solid-state process was used to effectively synthesize KMnO₂, a promising cathode material for KIBs. The materials were examined using X-ray powder diffraction (XRPD), Raman and infrared spectroscopies, electron microscopy analysis, optical, and impedance spectroscopies. Rietveld refinement of X-ray diffraction data confirmed that the compound crystallizes in the monoclinic system with the P-2₁/m space group. Fourier transform infrared and Raman spectroscopies revealed the vibrational modes of the KMnO₂ compound and proved the existence of the octahedral environment MO₆ (M = Mn, K), which affirms structural configuration. The morphological distribution and grain size of the titled compound were examined using SEM studies. A direct band gap of around 3.12 eV was found by optical studies using UV–Vis spectroscopy, confirming the semiconducting nature of KMnO₂ and indicating its applicability for optoelectronic and energy-related applications. The characteristics of this material were further examined using impedance spectroscopy at temperatures between 343 and 443 K and a frequency range of 10⁻¹ Hz to 10⁶ Hz. The DC conductivity and relaxation time exhibited Arrhenius behavior, with a significant shift in activation energy at 373 K, suggesting a change in the conduction mechanism. The frequency behavior of AC conductivity, σ_ac, was analyzed using the universal Jonscher law. The findings of the charge transportation study on KMnO₂ indicate that this material follows a non-overlapping small polaron tunneling (NSPT) for T < 383 K and correlated barrier hopping (CBH) above for T > 383 K. A correlation between the ionic conductivity and the crystal structure was established and discussed. Full article