Nanocrystalline Phase Research Articles

Continuously tunable negative pressure for engineering high-symmetry nanocrystalline phases

In this work, the phenomenon of strain induced by a mismatch in thermal expansion coefficients between a thin film and its substrate is harnessed in a new context, replacing the canonical planar support with a three-dimensional (3-D), nanoconfining scaffold in which we embed a material of interest. In this manner, we demonstrate a general approach to exert a continuously tunable, triaxial, tensile strain, defying the Poisson ratio of the embedded material and achieving the exotic condition of "negative pressure." This approach is hypothetically generalizable to materials of low modulus and high thermal expansion coefficient, and we use it here to achieve negative pressure in perovskite-phase CsPbI3 embedded within the cylindrical pores of anodic aluminum oxide membranes. Through controlled thermal hysteresis, the perovskite crystal structure can be continuously tuned toward higher symmetry when confined in a scaffold with pore size <40 nm, in contrast with the symmetry-reducing action of any other mechanical perturbation. We use this effect to control the octahedral rotation angle that is critical to the remarkable photovoltaic attributes of halide perovskites. Under hundreds of megapascals of apparent negative pressure, the bandgap tunability is observed to follow the same quantitative trend observed for hydrostatic positive pressure, exploring the negative pressure region and demonstrating the relative dominance of bond stretching effects over average octahedral rotation angle on electronic structure. This study reveals and quantifies the structural and electronic consequences of 3D tensile strain present by design and provides a framework for understanding adventitious strain present in all nanocomposite materials.

Influence of Bismuth Content on the Properties of Glass-Ceramics with Composition xBi2O3-(0.40-x)B2O3-0.15ZnO-0.45P2O5: Synthesis, Structural, Thermal Analysis, and Dielectric Relaxation Process

The glass-ceramics materials with the sample composition of xBi2O3-(0.40-x) B2O3-0.15ZnO-0.45P2O5 (BBZP) (where x = 0.10, 0.15, 0.20, and 0.25) have been prepared using the conventional melt-quenching technique. Different nanocrystalline phases embedded inside the glass-ceramic matrix have been characterised by analysing x-ray diffraction spectra. The obtained density values as well as molar volume increases with the rise of bismuth content. The network structure of the glass ceramic samples has been investigated employing Raman spectroscopy. The DSC analysis reveals the decrease in Glass transition temperature (Tg) (433K-416K), and crystallization temperature (Tc) (569K-556K) of the studied materials. The electrical properties of the samples have been investigated in the context of dielectric and modulus formalism. Different theoretical models have been employed to analyse the experimental data of dielectric and modulus spectra. The Nyquist plots of the materials have also been analysed employing relevant models. It has been shown that the higher bismuth containing samples are highly dense with high thermal stability. Such materials also have high dielectric strength. Analysis of these performance indicators suggests the possible applications of these materials in electrochemical devices.

Structural Characterization and Optical Properties of BiFeO3 Nanoparticles Synthesized by Propylene Glycol-Gel Route

This work focuses on the synthesis of phase-pure rhombohedral (R3c) nanocrystalline BiFeO3. The BiFeO3 nanoparticles were synthesized using the sol-gel method with propylene glycol as the complexing agent. The formation mechanism was investigated through thermal analysis and IR spectroscopy. The phase purity, crystal structure and nanocrystalline properties were studied using X-ray diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM). The elemental composition and bonding states were analyzed with X-ray photoelectron spectroscopy (XPS). The XRD and Raman spectra confirmed the formation of pure and well-crystallized BiFeO3 nanoparticles at 400 ºC. The optical band gap, determined by UV-visible spectroscopy, was found to be 2.08 eV, indicating that the synthesized BiFeO3 nanoparticles could be an effective photocatalyst in the visible light region.

Enhanced pseudocapacitive Li+ charge storage on lithium-rich disordered rock salt vanadium oxide nanocrystalline

Cation disordered rock-salt (DRS) metal compounds, featuring a three-dimensional percolation network for Li+ transportation, have attracted extensive attention as novel anode candidates for high-power lithium-ion batteries (LIBs) and capacitors (LICs). However, their low capacity and poor conductivity remain bottlenecks for their wide-scale usage, especially for high-energy applications. Here, we report a nanocrystal DRS Li3V2O5 (a-DRS-LVO) achieved by an electrochemically induced transformation on amorphous V2O5. The nanocrystalline phase of a-DRS-LVO can provide large active sites for Li+, leading to a surface-controlled solid-state Li+ diffusion behavior. In particular, the specific capacity for a-DRS-LVO reaches 716.8mAh g−1 at 0.1 A/g, exceeding that of DRS-LVO achieved by electrochemically induced transformation on well-crystallized V2O5. Further, a-DRS-LVO can work stably over 1,200 charge–discharge cycles with negligible capacity decay, due to the highly structural integrity stability, no phase change and limited volume change (∼8.2 %). A LIC with this a-DRS-LVO anode yields both high energy density (183 Wh kg−1) and power density (50,000 W kg−1), which are much higher than that of the state-of-art LICs based on graphite and other pseudocapacitive anodes, such as niobium and titanium oxides.

Fe(II)-Catalyzed Recrystallization Drives Phosphorus and Aluminum Release from Goethite.

Goethite often harbors impurities, such as phosphorus (P) and aluminum (Al), which are incorporated into its structure through direct substitution or coprecipitation with nanocrystalline phases. Understanding the processes that drive the release of P and Al from goethite is of paramount importance for the iron ore industry and for managing nutrient and pollutant behavior in the environment. This study investigates the impact of Fe(II)-catalyzed recrystallization on the release of P and Al from goethite. We evaluated the solubility and extractability of P and Al in suspensions of Al- and P-coprecipitated goethite, treated with 57Fe-enriched Fe(II)aq under oxygen-free conditions for 30 days at neutral pH and room temperatures. The addition of Fe(II)aq induced the recrystallization of goethite dominant initial synthetic phases (i.e., low P- and Al-containing phases) and the transformation of higher P- and/or Al-bearing starting material that was actually a mixture of goethite and minor amounts of lepidocrocite and feroxyhyte. Our results reveal that Fe(II)-catalyzed mineral and structural evolution led to the repartitioning of P and, to a lesser extent, Al throughout the crystal structure, mineral surface, and aqueous solution. Following a 30 day reaction with Fe(II)aq, we extracted approximately 80, 68.8, 73.9, and 83.2% of P from P-only, low, medium, and high P + Al goethite, respectively. Additionally, we observed total Al removals of approximately 17, 27, and 25% from low, medium, and high P + Al goethite, respectively. The results demonstrate that treating both P-only and P + Al goethite with Fe(II) at room temperature, followed by a 24 h extraction using 1 M NaOH, significantly enhances the overall extractability of P and Al, including both aqueous and surface-adsorbed fractions, compared to Fe(II)-free controls. These findings advance our understanding of the recrystallization process and impurity substitution in goethite, offering promising avenues for developing new environmentally friendly methods to extract P and other impurities from goethitic iron ores at lower temperatures.

Unraveling the Formation of Ternary AgCuSe Crystalline Nanophases and Their Potential as Antibacterial Agents.

AgCuSe nanoparticles could contribute to the growth of strongly light-absorbing thin films and solids with fast ion mobility, among other potential properties. Nevertheless, few methods have been developed so far for the synthesis of AgCuSe nanoparticles, and those reported deliver nanostructures with relatively large sizes and broad size and shape distributions. In this work, a colloidal cation exchange method is established for the easy synthesis of AgCuSe NPs with ca. 8 nm diameters and narrow size dispersion. Notably, in this lower size range the conucleation and growth of two stoichiometric ternary compounds are generally observed, namely the well-known eucairite AgCuSe compound and the novel fischesserite-like Ag3CuSe2 phase, the latter being less thermodynamically stable as predicted computationally and assessed experimentally. An optimal range of Cu/Ag precursor molar ratio has been identified to ensure the growth of ternary nanoparticles and, more specifically, that of the metastable Ag3CuSe2 nanophase isolated for the first occasion. The attained size range for the material paves the way for utilizing AgCuSe nanoparticles in new ways within the field of biomedicine: the results obtained here confirm the antibacterial activity of the new Ag x Cu y Se z nanoparticles against Gram-positive bacteria, with significantly low values of the minimal inhibitory concentration.

Fe-based metallic glass coatings with suppressed cracks and enhanced wear resistance prepared by extreme high-speed laser cladding

Fe-based metallic glass (MG) coatings draw great attentions due to their excellent wear resistance. The recently developed extreme high-speed laser cladding (EHLC) provides a promising method for their fabrication but limited by the strong tendency to crack. Besides that, the deep insight into the structure evolution and the failure mechanism of the coating is still lacked. Thus, the understanding of the crack origin and the prevention of crack are of great importance. In the present work, Fe-Mo-Cr-Y-C-B MG coatings with adjustable glassy phase content were successfully fabricated by EHLC. The microstructure characterization of the coatings reveals that the cracks is main caused by the hard and brittle nanocrystalline phases precipitations of monoclinic Mo12Fe22C10 and (Fe, Cr)23C6 carbides in the heat affected zone. Therefore, the cracking of the coatings can be effectively reduced by increasing the glassy phase content. Subsequently, the hardness distribution, wear performance and wear mechanism of the coatings were investigated. The results showed that increasing the glassy phase content can effectively achieve low wear rate. The prepared Fe-Mo-Cr-Y-C-B MG coatings exhibit abrasion loss as low as 3.54·10−6 mm3 (N m)−1, which is an order of magnitude lower than that of the 45# steel substrate. The wear of the coatings is primarily attributed to the fatigue wear accompanied with slighting oxidative wear. By suppressing the brittle precipitated crystalline phases in the coating, the fatigue wear can be reduced and the wear resistance of the coatings can be improved. The present work provides insights into the crack prevention and were performance improvement of the Fe-based MG coatings prepared by EHLC.

Preparation and mechanical properties of Al-doped TiC films

Abstract Al-doped TiAlxC films were prepared on different substrates (single crystal Al2O3 (0001), stainless steel, and silicon wafer substrates) by co-sputtering, and microstructures and corresponding mechanical properties of TiAlxC films were tested and analyzed. The results indicate that the microhardness of the prepared TiAlxC films would decrease with the increased doping amount of Al while the corresponding friction coefficient would increase. With the increase of Al doping, the excess Al hinders the growth of the nanocrystalline phase in the TiAlxC film, thereby affecting the hardness and wear resistance of the TiAlxC film. When the Al doping is 4.1 at%, the hardness of the film reaches 2, 890 HV, while the friction coefficient is 0.2, indicating that a small amount of Al plays a role in solution strengthening the film. Therefore, the mechanical properties of the Al-doped TiAlxC films could be tailored by the doping amount of Al.

Wide-Field Polarimetric Second-Harmonic Imaging for Rapid and Nondestructive Investigation of Laser-Induced Crystallization Phenomena.

The selective and controlled formation of nanocrystals in glass is emerging as a versatile method to achieve functional photonics, optoelectronics, and quantum devices, such as single-photon emitters. Here, we investigate the use of wide-field polarimetric second-harmonic (SH) microscopy as a method to rapidly and nondestructively examine nanoscale crystal arrangements in laser-processed glass. As a case study, we investigate tellurite glass, where the formation of a trigonal tellurium (t-Te) nanocrystalline phase after femtosecond laser exposure was recently demonstrated. Combined with theoretical models, we show that wide-field polarimetric SH microscopy offers comprehensive information on the nanocrystals' orientation, distribution, and chirality. With its high imaging throughput and spatial resolution, this method has the potential not only to significantly accelerate investigations on laser-induced glass crystallization processes but also to provide a valuable tool for in situ process monitoring.

Scalable nano-crystallization approach over multiple passivation behavior for Fe-based amorphous coating under chloride exposure

Structure-aware complicated Fe-based amorphous coating induced by scalable nano-crystallization approach proved influential in this work. The integration of experimental and mathematical findings uncovered that the dual nanocrystalline phases, interacting within the amorphous matrix of the coating subjected to annealing at 893 K, demonstrated the most superior electrochemical performance against chloride ion attack. At this singularity temperature, compositional intricacies were strengthened by structural relaxation, a consequence of the compatible collaboration of chemical constituents. The categorization of the vacancy-triggered point defects model (VR-PDM) indicated that the involvement and subsequent collapse of oxygen vacancies played a pivotal role in governing the multifaceted passivation behavior. A circulation of film spatial extension evaluated by d′-parameter in assistance with diffusion coefficients D of oxygen vacancies provided the direct evidence that reliable nano-crystallization strategy can reach a critical safety point against corrosion degradation. The total adaptive contribution of passivity to corrosion attack can be beneficial from the precise segmentation of surficial positions superimposed by target metallic atoms in competition with Cl- ions.

Quantitative structural characterization of LiNbO3-SiO2 glass-ceramics by multinuclear solid-state NMR

This study presents a detailed structural analysis of the glass-to-crystal transition in the technologically important LiNbO3–SiO2 glass system, focusing on the composition 35Li2O–25Nb2O5–40SiO2 known for its exceptional second harmonic generation (SHG) response in glass-ceramics. We develop a comprehensive solid-state NMR protocol to quantify major and minor fractions of elusive nanocrystalline phases and the residual glass composition, overcoming limitations of techniques such as X-ray diffraction and Raman spectroscopy. By employing 7Li satellite transition difference spectroscopy and 93Nb magic-angle spinning (MAS) NMR, we achieve quantification of crystalline fractions down to 1%. By combining all the complementary 6Li, 7Li, 29Si, and 93Nb MAS NMR experiments, we also deduce the composition of the residual glass. Short crystallization times (up to 120 min) at 640 °C result in nanocrystalline LiNbO3, whereas crystallization for 1440 min at this temperature additionally yields two Li2Si2O5 polymorphs and Li2SiO3. 7Li spin echo and 7Li{93Nb} W-RESPDOR NMR spectroscopy indicate that LiNbO3 crystallizes in specific domains leaving behind SiO2-rich residual glassy domains. This work offers a time-efficient and versatile NMR protocol for characterizing crystalline and residual glass components in nanocrystalline glass-ceramics in the LiNbO3–SiO2 system and beyond, providing valuable insights into the crystallization process which is not possible with other techniques.

Glass and nanocrystalline phase formation in CuZrAg alloys: Insights from combinatorial thin film libraries studied by mapping synchrotron X-ray diffraction

We report detailed diffraction peak analysis and parameters indicative of the transition between fully amorphous microstructures and nanocrystal formation in sputter deposited thin film metallic glasses. Specifically, we fabricated ternary CuZrAg alloy films (2µm thickness) with a large compositional gradient on flexible, X-ray transparent polymer substrates in high vacuum conditions. The combinatorial libraries were subjected to point-by-point structural (XRD synchrotron radiation) and chemical (X-ray fluorescence spectroscopy) analysis, characterizing roughly 172 alloys. A strong correlation was found between peak symmetry and width, and early stages of crystalline phase formation. These nanocrystals are difficult to detect from the evolution of the peak position. In view of current literature, our data questions the recently claimed universality of the peak width as indicator of high glass forming ability. The addition of Ag significantly improves the poor glass formation of binary CuZr (36 alloys) under identical deposition conditions, as fully amorphous alloys are found for the majority of the investigated composition space. A thorough understanding of the microstructure of CuZrAg alloys on flexible substrates is highly relevant in view of favourable antibacterial properties and potential application as coatings for biomedical surfaces.

Thermodynamic description of U(IV) solubility and hydrolysis in chloride systems: Pitzer activity model for the system U4+–Na+–Mg2+–Ca2+–H+–Cl––OH––H2O(l)

This study presents updated chemical, thermodynamic, and activity models for the system U4+–Na+–Mg2+–Ca2+–H+–Cl––OH––H2O(l) derived using the Pitzer formalism and a strict ion interaction approach. The models build on comprehensive solubility datasets in dilute to concentrated NaCl, MgCl2, and CaCl2 solutions. The Nuclear Energy Agency-Thermochemical Database (NEA-TDB) selection of solubility and hydrolysis constants in the reference state were taken as anchoring point, and were extended further with the solid nanocrystalline phase UO2∙H2O(ncr) and the ternary complex Ca4[U(OH)8]4+. The former was identified in long-term solubility experiments at ambient conditions, whereas the latter has been selected in analogy to Th(IV), Np(IV), and Pu(IV) considering experimental evidences available for these An(IV) in alkaline, concentrated CaCl2 solutions. These models represent an improved tool for the calculation of U(IV) solubility and aqueous speciation in a variety of geochemical conditions including concentrated brine systems relevant in salt-based repositories for nuclear waste disposal.

Effect of substrate temperature on the structural properties of Tungsten Carbide and Tungsten-rich Tungsten Carbide films

ABSTRACT The unique mechanical properties of Tungsten Carbide (WC), such as fracture toughness, exceptional hardness, high melting temperature, outstanding thermal stability, anti-oxidation qualities fatigue and creep resistance, have made it a suitable industrial material for different applications. It is also considered to be a promising material for coating on plasma-facing walls in a Tokamak reactor. The aim of the present work is to study the effect of varying substrate temperature, concentration of tungsten (W) and annealing in the structural properties of WC films. The WC films are deposited on a silicon substrate at different substrate temperatures viz. RT (300 K), 400, 500, 600 and 700 K using DC magnetron sputtering. W-rich WC films were deposited keeping the power of WC constant (100 Watt) and varying W powers (10 Watt, 20 Watt, 30 Watt, 40 Watt) at room temperature. Later, these W-rich WC films were annealed at 800°C in a reducing atmosphere. Glancing incidence X-ray diffraction (GIXRD) and Raman spectroscopy of the films are performed for structural analysis. GIXRD of the WC films reveals that as-deposited RT films are amorphous. However, films which are either deposited at elevated substrate temperature or are annealed are crystalline. This is confirmed by Raman’s measurements. It also indicates the presence of disorder and nanocrystalline phases due to temperature variations.

The role of the reaction medium pH in the formation of nanocrystalline phases in the Bi2O3-P2O5-H2O system

The role of the reaction medium pH in the formation of nanocrystalline phases in the Bi2O3-P2O5-H2O system

Crystallization processes of rare-earth doped GdF3 nanocrystals in silicate glass matrix: Dimorphism and photoluminescence properties

Rare-earth doped GdF3 nanocrystals embedded in silica glassy matrix have been prepared by controlled crystallization of the xerogel; the influence of rare-earth ion (Pr, Sm, Eu, Tb, Dy, Er, Yb) and additional Li-codopant on structural and optical properties was discussed. The precipitation of RE-doped GdF3 nanocrystalline phase is the result of Gd-trifluoracetate thermolysis revealed as a strong exothermic peak at around 300 °C. Structural analysis of RE-doped SiO2-GdF3 glass-ceramic sample calcined at 525 °C showed the occurrence of GdF3 nanocrystals of about 25 nm size, showing hexagonal or orthorombic structure depending on the RE-ion. Under UV-light excitation at 273 nm of Gd3+ ions (8S7/2 → 6I13/2,15/2 transition), photoluminescence spectra showed characteristic RE3+ luminescence due to the non-radiative energy transfer between the excited Gd3+ and acceptor RE ions; the highest energy transfer (≅ 80 %) was observed for Tb3+ and lowest (≅ 21 %) for Sm3+.

Microstructural evolution and strengthening behavior induced by N addition in TiVCrAl medium entropy alloy films

In this study, we have studied the influence of nitrogen content on the mechanical properties of nanostructure medium entropy (TiVCrAl)Nx films prepared by magnetron sputtering. A transition from body-centered cubic nanocrystalline phases to an face-centered cubic columnar crystal structure has been observed in the medium entropy films as the nitrogen flow increases. With increasing nitrogen flow, the lattice constant of the film first increases and then decreases due to the change of composition from substoichiometric to overstoichiometric, resulting in the different bond length of Metal-N. The hardness of the films first increases and then decreases with the increase of nitrogen flow. When the nitrogen flow was 25 sccm, the hardness reached the maximum value of 23.1 GPa. Moreover, the film has shorter cracks length and a higher hardness/modulus ratio, exhibiting enhanced fracture toughness. The increased hardness primarily results from the formation of bonds between metals and nitrogen and the strengthening of a solid solution and a grain boundary.

Effect of the volume fraction of nanocrystals on the mechanical properties of (Fe0·9Ni0.1)86B14 amorphous/nanocrystalline alloy

The effect of the volume fraction of nanocrystals on the macroscopic mechanical properties and microscopic atomic structure of Fe-based nanocrystalline alloys, as well as the relationship between the two, is an urgent issue to be explored. Seven nanocrystalline alloys with different volume fractions of nanocrystals were formed by annealing treatment of (Fe0·9Ni0.1)86B14 amorphous precursor. Through hardness, flat plate bending, and nanoindentation experiments, it is found that when the volume fraction of nanocrystals reaches the range of 45–55 %, there is an abrupt change in the macroscopic mechanical properties. Specifically, when the volume fraction is less than this range, the properties inherit the amorphous matrix, however, larger than this range, the properties are dominated by precipitated nanocrystalline phases. Meanwhile, based on the molecular dynamics simulation method, seven Fe90Ni10 amorphous nanocrystalline models with different volume fractions of body-centered cubic nanocrystals are established, and the deformation mechanism of models and the evolution of their microstructures during the nanoindentation process are obtained intuitively. Moreover, it is further revealed that the significant changes in the Voronoi polyhedral index, which represents the microscopic atomic structure in this range of nanocrystal volume fractions, are the main reason for the abrupt changes in the mechanical properties at the macroscopic level.

Synthesis of transparent tin-doped indium oxide (ITO)-containing glass-ceramic coating by the sol-gel route for UV/NIR-shielding

Transparent glass-ceramic containing tin-doped indium oxide nano-crystalline phase was synthesized using the sol-gel method. The prepared sol, which was based on sodium aluminoborosilicate glass composition, was applied on soda-lime-silicate glass substrate through the dip-coating technique. Developing such glass-ceramics can offer several advantages, including reducing the total cost of production, enhanced chemical durability and a low-temperature synthesis process. The thermal behavior of the dried gels was investigated using simultaneous thermal analysis (STA), to determine the decomposition temperature of the nitrate salts in the gel, its glass crystallization temperature, and finally to optimize the heat treatment regime and optical properties as well. UV–Vis–NIR spectroscopy of the coated samples after heat treatment at 500 °C for 10 h revealed high visible transparency (T>70%) while indicating significant UV/NIR shielding, i.e. near zero and 10 % transmission, respectively. Phase analysis and crystallization behavior studies were conducted using XRD and FE-SEM to evaluate the morphology and size of the precipitated crystallites. According to the results, the optimum heating program for ITO crystallization was heating temperature and soaking time of 500 °C and 10 h, respectively. The undesirable crystalline phase of InBO3 was precipitated as the main crystalline phase by increasing the heat treating temperature to 550 °C. Furthermore, the glass structure was studied using FTIR spectroscopy demonstrating a highly polymerized glassy network for the coating. The effect of the precursors-to-solvent ratio during the synthesis process on the final optical properties was also investigated.

Transparent aluminoborosilicate glass-ceramics containing Al4B2O9 nanorods

Transparent glass-ceramics containing nanorods are attractive for many applications. In this work, transparent aluminoborosilicate glass-ceramics containing aluminum borate nanorods are reported. Effects of Al2O3 and SiO2 concentrations on the thermal properties and crystallization of aluminoborosilicate glasses are studied. It is found that lithium aluminosilicate nanocrystals and Al4B2O9 nanorods are co-precipitated in glasses with Al2O3/SiO2 molar ratios of 0.29 and 0.33, and only Al4B2O9 nanorods are precipitated in glasses with Al2O3/SiO2 molar ratios of 0.375 and 0.42. Precipitation of these nanocrystalline phases leads to the enhancement in Vickers hardness. Glass-ceramics with Al2O3/SiO2 molar ratios of 0.375 and 0.42 are highly transparent in the visible region due to the small size of the Al4B2O9 nanorods precipitated inside.