Crystal Refinement Research Articles

Double Free: A Promising Route toward Moisture-Stable Hypotoxic Hybrid Perovskites

Double Free: A Promising Route toward Moisture-Stable Hypotoxic Hybrid Perovskites

Robust thermal performance of red-emitting phosphor composites for white light-emitting diodes: Energy transfer and oxygen-vacancy induced electronic localization

Ce3+ ion can effectively sensitize Sm3+ ion via energy transfer, and this phenomenon can led to the development of white light-emitting diodes (WLED). However, interestingly, high correlated color temperature (CCT), poor color-rending index (CRI), poor thermal stability, and low efficacy of available red phosphor still pose immense challenges. Herein, we undertook a combined analysis: X-ray diffraction (XRD), crystal refinement, electron spin resonance (ESR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and diffuse reflection spectroscopy (DRS). We also observed the optical properties of the resulting samples. The Ce3+ and Sm3+ dopants on the Sr2+ and La3+ sites in the mixed cation borate Sr3LaAl3B4O15 (SLAB) phosphors were quantitatively evaluated. A cerium ion merged as a sensitizer, improving the red emission intensity by enhancing it 3.9 times. The energy transfer (ET) between Ce3+ and Sm3+ was examined experimentally and with theoretical models as a function of Ce3+ concentrations at ambient temperatures. Several theoretical models were employed to simulate the luminescence decays of Ce3+ and Sm3+ doped samples at different doping levels and their transfer mechanisms were studied depending on forced electric dipole at each ion. Notably, the electronic sites created by the oxygen vacancies around the Ln3+ ions can effectively justify the highly efficient bluish-red phosphor. Additionally, the SL0.95AB:0.02Ce3+,0.03Sm3+ exhibited outstanding thermal-quenching (TQ) resistance and has > 94.8% intensity at 425 K. WLEDs made with the use of SL0.95AB:0.02Ce3+,0.03Sm3+ furnished an exceptional CRI exceeding 88 and low at CCT 4503 K. These results are superior to the parameters of commercial WLED containing Y3Al5O12:Ce3+ phosphor and blue LED chip (CCT≈7746 K, CRI≈75), and they could be a cornerstone for the fabrication of warm WLEDs.

Influence of Surface Post-Processing on Crystal Refinement and Characteristics of Hopeite Coating by Phosphating

Hopeite (Zn3(PO4)2·4H2O) conversion coating was prepared on pure titanium using mild phosphate chemical conversion technology. In this investigation the effect of post-processing after phosphating was focused on coating microstructure, chemical composition, adherence and corrosion resistance. Different sequential order of drying and rinsing of the coated samples were carried out. The results demonstrated that the priority shift of rinsing or drying did not change the hopeite phase of the conversion coating, but played a significant role in the crystal size and coating microstructure. Compared with the traditional preparation of the coating, a more compact and uniform coating with finer crystals grains (3–5 μm) was obtained by the unconventional post-treatment of drying before rinsing, along with a higher bonding strength and corrosion resistance.

Confirmation of Siderazot, Fe3N1.33, the Only Terrestrial Nitride Mineral

Siderazot, the only terrestrial nitride mineral, was reported only once in 1876 to occur as coating on volcanic rocks in a fumarolic environment from Mt. Etna and, to date, has been neither confirmed nor structurally characterized. We have studied the holotype sample from the Natural History Museum, London, UK, originally collected by O. Silvestri in 1874, and present siderazot with ε-Fe3N-type crystal structure and composition of Fe3N1.33(7) according to crystal structure Rietveld refinements, in good agreement with electron microprobe analyses. Crystal structure data, chemical composition, and Raman and reflectance measurements are reported. Possible formation conditions are derived from composition and phase stability data according to synthetic samples.

Mn-induced spin glass behavior in metallic Ir3Sn7−x Mn x

Transition metal stannides are usually semiconductors with a narrow band gap. We report experimental investigation on metallic Ir3Sn7–x Mn x (x = 0 and 0.56). Single crystal x-ray diffraction refinement indicates that Ir3Sn7–x Mn x crystals form a cubic structure (space group Im m) with the lattice parameter a = 9.362(4) Å for x = 0 and 9.328(6) Å for x = 0.56. The electrical resistivity shows metallic behavior between 2 K and 300 K with T 2 dependence at T < 30 K for x = 0, reflecting the Fermi-liquid ground state. While Ir3Sn7 exhibits weak diamagnetism, partial substitution of Sn by Mn results in spin glass behavior in Ir3Sn7−x Mn x below T g ∼ 13 K for x = 0.56. Remarkably, an upturn in the resistivity is observed in x = 0.56 below ∼2T g, suggesting strong spin fluctuation. This fluctuation is suppressed by the application of magnetic field, which is reflected in the observation of negative magnetoresistance. The unusual properties that emerge due to Mn doping are discussed.

Structural dependence of microwave dielectric performance of wolframite structured Mg1-xCaxZrNb2O8 ceramics: Crystal structure, microstructure evolution, Raman analysis and chemical bond theory

Wolframite-structured Mg1-xCaxZrNb2O8 (0−0.1) ceramics were synthesized through a solid-state procedure. Crystal refinement indicates a pure Mg1-xCaxZrNb2O8 ceramic with a wolframite structure. Ca2+ substitution led to the redshift of the Ag mode at approximately 896 cm−1. Additionally, Ca2+ substitution could promote grain growth and contribute to microstructure evolution from a polyhedral shape to a rod shape. According to chemical bond theory, an appropriate Ca2+ concentration can increase NbO bond iconicity and NbO bond lattice energy, which contributed to the great improvement in the dielectric constant and Q × f value. Additionally, the τf value was affected by the bond valence and thermal expansion coefficient of the MgO bond. The Mg1-xCaxZrNb2O8 (x = 0.04) ceramics exhibited great improvement in the Q × f value: εr = 25.21, Q × f = 116,000 GHz (@7.17 GHz) and τf = −24.4 ppm/°C, which provides enormous potential for future millimeter-wave applications.

Structural analysis and magnetic characterization of ternary alloys (Co–Fe–Ni) synthesized by mechanical alloying

In this research, the synthesis of Co–Fe–Ni ternary alloys in different compositions (Co40Fe30Ni30, Co30Fe40Ni30 and Co30Fe30Ni40), and their structural and magnetic properties were assessed. These alloys were milled during 7 h by mechanical alloying (MA), after of the milling time, the results of the structural analysis, shown three solids solutions obtained with fcc-structure (Co(FeNi)–fcc, Fe(CoNi)–fcc and Ni(FeCo)–fcc). As a consequence of the process of synthesis, the crystal size refinement was observed in all cases, meanwhile, the particle size increased due to the powders ductility.The magnetic properties at room temperature were studied to observe the saturation magnetization (Ms), before and after of the milling, the results of the un-milled powders were 140, 130 and 110 A m2/kg for Co40Fe30Ni30, Co30Fe40Ni30 and Co30Fe30Ni40 respectively, after of mechanical alloying, the MS increased to 162, 166 and 150 A m2/kg. On the other hand, the coercive field (HC) values decreased drastically from 6.13 kA/m (~77 Oe), 4.77 kA/m (~60 Oe) and 5.57 kA/m (~70 Oe) before of the milling process, to 0.365 kA/m (~4.6 Oe), 0.296 kA/m (~3.7 Oe) and 0.306 kA/m (~3.8 Oe) after the milling for Co40Fe30Ni30, Co30Fe40Ni30 and Co30Fe30Ni40, respectively.

Inhibition effect of aminated montmorillonite on crystallization of dendritic polyamide 6

Dendritic polyamide 6 (PA6)/montmorillonite (MMT) hybrid material has been prepared via in situ grafting polymerization by using dendritic initiator and amino-functional MMT (AMT). The effect of AMT on the crystallization properties of dendritic PA6 was characterized by WAXD、POM and TEM. The results illustrate that the amino functional groups of MMT are the initiator of the PA6 polymerization, which function as branching point and inhibiting the spherulites growth. When adding AMT to PA6, the α polymorph of PA6 degraded and crystalllinity of PA6 declined. As the content of AMT increased, the strength and toughness of composites increased gradually due to the effect of AMT on crystal particle refinement.

Synergistic effect of surfactant and saccharin on dispersion and crystal refinement for electrodeposition of nanocrystalline nickel/graphene oxide composite

Homogeneous dispersion of graphene oxide (GO) in nickel sulfamate solution is a significant challenge for electrodepositing high-performance nickel/GO composite coatings. In the present work, three typical surfactants, including anionic surfactant Sodium dodecyl sulfate (SDS), cationic surfactant Cetyltrimethylammonium bromide (CTAB), and non-ionic surfactant Polyethylene glycol (PEG), and saccharin are used to disperse GO nanoparticles and refine crystallite size of nickel/GO composite coating. The synergistic effect of surfactant and saccharin is revealed from the perspectives of dispersion, crystal refinement and their impact on mechanical and tribological properties of nickel/GO composite coating. Our results indicate that PEG possesses the optimal dispersibility to GO dispersion, followed by CTAB and SDS. The addition of saccharin in electrolyte does not affect the surface charge of GO particles, but it helps to reduce the particle size of GO and thus reduce potential reaggregation. Additionally, PEG shows the most significant reduction of crystallite size from ~35 nm to ~19 nm. The synergetic effect of surfactant and saccharin is indicated by increasing the concentration of saccharin from 0 to 0.2 g/L with various surfactants, where the overall crystallite size is gradually reduced. Moreover, the hardness of PEG-GO and CTAB-GO coatings is remarkably increased by 252% and 312%, respectively, compared to pure nickel coating. The increased hardness is due to the synergistic effect of crystal refinement from both additions of GO and saccharin. The tribological test indicates that the PEG-GO coating can achieve the maximum reduction of friction coefficient with 0.15 with the addition of saccharin of 0.2 g/L.

Canted Eu magnetic structure in EuMnSb2

Magnetic ordering breaks the time-reversal symmetry, greatly impacting material topological properties. We report the investigation of the magnetic properties of the layered $\mathrm{EuMnS}{\mathrm{b}}_{2}$, which has two sets of magnetic sublattices. Both the magnetization and electrical resistivity reveal two phase transitions with one at ${T}_{\mathrm{N},\mathrm{Eu}}\ensuremath{\sim}21\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and the other at ${T}_{\mathrm{N},\mathrm{Mn}}\ensuremath{\sim}346\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Single crystal neutron diffraction refinement indicates that both transitions are originated from magnetic ordering. Below ${T}_{\mathrm{N},\mathrm{Mn}},$ the Mn sublattice forms the C-type antiferromagnetic (AFM) structure with moments [$(4.5\ifmmode\pm\else\textpm\fi{}0.6){\ensuremath{\mu}}_{B}$ at 7 K] pointing along the $a$ axis. Below ${T}_{\mathrm{N},\mathrm{Eu}}$, the Eu sublattice forms the canted A-type AFM structure with moments [$(5.9\ifmmode\pm\else\textpm\fi{}0.8){\ensuremath{\mu}}_{\mathrm{B}}$ at 7 K] lying in the $ac$ plane but pointing (41 \ifmmode\pm\else\textpm\fi{} 1)\ifmmode^\circ\else\textdegree\fi{} away from the $a$ axis. Quantitative analysis indicates that the spin-spin correlation length, while anisotropic, has long-range characteristic in all directions for both the Eu and Mn sublattices.

Phase evolution and origin of the high piezoelectric properties in lead-free BiFeO3–BaTiO3 ceramics

La-substitution effects for Bi3+-site in 0.7Bi1.03(1-x)LaxFeO3-0.3BaTiO3 (abbreviated as BF30BT-100xLF with x = 0.00, 0.01, 0.035, 0.06, 0.07 and 0.10) ceramics were investigated systematically. All ceramics were synthesized by a conventional solid-state reaction method and quenched in water from its sintering temperature. The crystal structure Rietveld refinement shows that undoped BF30BT ceramic exhibited dominant rhombohedral (R) symmetry and gradually changed to the tetragonal (T) phase with La-doping. However, for x ≥ 0.07 compositions the lattice distortions (cT/aT and 90°−αR) significantly decrease as a result crystal structures become close to the cubic-like (CL) phase. Hence, two different morphotropic phase boundaries (MPBs) were reported for BF30BT-100xLa ceramic system; one MPB-I between the R and T phases and the other MPB-II between T and CL phases. The largest direct piezoelectric coefficient (d33 = 274 pC/N) with a high Curie temperature (TC = 532 °C) for BF30BT-1LF composition was obtained due to the typical MPB-I between R and T phases. However, a maximum electric field-induced strain (Smax = 0.27%) with a high converse piezoelectric coefficient (d33* = 500 pm/V) for BF30BT-7LF ceramic was mainly attributed to the MPB-II of T + CL phases and soft ferroelectric switching properties.

Crystal refinement of rutile by sonochemical method to achieve high performance Pd catalysts for direct synthesis of hydrogen peroxide

Abstract In this study, sonochemically prepared (S) Pd catalysts supported on anatase (Ana) and rutile (Rut) were compared to incipient wetness impregnated (I) Pd catalysts for the direct synthesis of hydrogen peroxide. Pd/Ana-S and Pd/Rut-S achieved higher H2 conversion than Pd/Ana-I and Pd/Rut-I due to the improvement of metal dispersion by the sonochemical method. Especially, Pd dispersion on Pd/Rut-S was estimated to be six times higher than other catalysts, resulting in the highest H2O2 production rate. Through multiple characterizations (TEM, N2 adsorption-desorption, H2-TPR and CO-chemisorption), we discovered that many parts of the rutile crystals were cracked during the sonochemical treatment, obtaining rectangle shape rutile crystals and two times higher specific surface area. As a result, the sonochemical method played dual-functionalities as follows: physically cracking rutile crystals and inducing small Pd nucleation by cavitation. In addition, electron-deficient Pd species, beneficial for H2O2 selectivity, were dominantly observed on rutile by XPS analysis. This outcome was explained by unstable Ti3+ species on anatase favoring the electron-rich metal. Conclusively, it is demonstrated that the sonochemical method and rutile TiO2 have a substantial synergistic effect on both H2 conversion and H2O2 selectivity for the direct synthesis of hydrogen peroxide.

Microstructure and Mechanical Properties of Underwater Laser Welding of Titanium Alloy.

Underwater laser beam welding (ULBW) with filler wire was applied to Ti-6Al-4V alloy. Process parameters including the back shielding gas flow rate (BSGFR) (the amount of protective gas flowing over the back of the workpiece per unit time), focal position, and laser power were investigated to obtain a high-quality butt joint. The results showed that the increase of BSGFR could obtain the slighter oxidation level and refiner crystal grain in the welded metals. Whereas the back shielding gas at a flow rate of 35 L/min resulting in pores in the welded metals. With the increasing of the heat input, the welded metals went through three stages, i.e., not full penetration, crystal grain refinement, and coarseness. Crystal grain refinement could improve the mechanical properties, however, not full penetration and pores led to the decline in mechanical properties. Under optimal process parameters, the microstructure in the fusion zones of the underwater and in-air weld metals was acicular martensite. The near the fusion zone of the underwater and in-air weld metals consisted of the α + α′ phase, but almost without the α′ phase in the near base metal zone. The tensile strength and impact toughness of the underwater welded joints were 852.81 MPa and 39.07 J/cm2, respectively, which approached to those of the in-air welded joints (861.32 MPa and 38.99 J/cm2).

Synthesis of Manganese‐Based Prussian Blue Nanocubes with Organic Solvent as High‐Performance Anodes for Lithium‐Ion Batteries

Prussian blue analogue KxMnFe(CN)6·yH2O (m‐KMHCF) nanocubes with an average edge length of about 60 nm were synthesized by a simple hydrothermal reaction involving methanol. The microscopic size of m‐KMHCF nanocubes could be easily reduced to less than 100 nm as methanol was added to the reaction, over a long range of reaction temperatures and reaction times. As anode material for lithium‐ion batteries, the m‐KMHCF electrode delivered a high specific capacity of over 900 mAh g–1 at a current density of 100 mA g–1 after 50 cycles. In addition, it provided stable rate capability and lithium storage performance at the high current density of 382.3 mAh g–1 at 5000 mA g–1. It is worth noting that the capacity continued to rise during the galvanostatic charge‐discharge, and the specific capacity increased after charging and discharging at the large current. This phenomenon and the excellent electrochemical performance are mainly derived from the smaller microscopic size, which further led to crystal particle refinement during charge‐discharge.

Two homochiral crystals of anion-directed Cu(I) and Zn(II) helical coordination polymers

Two chiral coordination polymers [CuI(TMBP)(CH3CN)2·ClO4]n (1) and [ZnII(TMBP)(SCN)2]n (2) have been synthesized with 3,3’,5,5’-tetramethyl-4,4’-bipyrazole (TMBP) as ligand. Their structures were determined by single-crystal X-ray diffraction (SCXRD) analysis and further characterized by power X-ray diffraction (PXRD) analysis, FT-IR spectroscopy, and thermogravimetric (TG) analysis. 1 is constructed by left-handed double-stranded helices with the same chirality, while 2 possesses right-handed single-helical chains. The existence of ClO4− in 1 might be the main reason for forming double-stranded helices, while it leads to single-helical chains under induction of SCN−, exhibiting a anion-directed synthesis process. The selected two single crystals are both homochiral according to the Flack parameters (≈0) from crystal refinement. The bulk sample of 1 exhibits a negative solid-state Cotton effect, while that of 2 shows a positive one. In addition, the crystal sample of 1 exhibits strong ligand-based and metal to ligand charge transition (MLCT) emission in solid-state luminescence with comparison to weakly luminous 2 at room temperature.

Solution‐Processed Perovskite Microdisk for Coherent Light Emission

AbstractHigh‐quality semiconductor microdisks (MDs) are of crucial importance for realizing on‐chip coherent light sources. However, the fabrication of all‐inorganic semiconductor circular or circular‐like microdisks (CMDs) with suitable size for optoelectronic applications is still complex and expensive. Herein, a facile ligand‐free antisolvent‐assisted growth method is used to synthesize high‐quality Cs4PbBr6 MDs with tunable size and morphology, which is evolved from rhombohedral to octahedral, hexagonal‐like, and circular‐like MDs based on Cl‐containing antisolvents. Significantly, this is the first time that large semiconductor CMDs are synthesized from solution self‐assembled growth at room temperature. These Cs4PbBr6 MDs show high‐efficient and stable green emission (522 nm), which should be attributed to the first‐order excitonic emission from embedded CsPbBr3 nanocrystals (NCs). The distribution of CsPbBr3 NCs is verified by lattice fringe, crystal data refinement, and time‐resolved photoluminescence analysis. These CsPbBr3‐in‐Cs4PbBr6 CMDs are demonstrated to hold outstanding two‐photon pumped coherent light emission ability with a remarkably low threshold (400 µJ cm−2). These findings suggest CsPbBr3‐in‐Cs4PbBr6 MDs have excellent light emission capability and stability toward practical optoelectronic applications, and their tunable morphology and size indicate that solution method is feasible for the fabrication of semiconductor CMDs.

Single-band red upconversion luminescence of β-NaLuF4:Gd, Yb, Er@SiO2 submicron particles via annealing without agglomeration

Although the effect of annealing on upconversion luminescence (UCL) of lanthanide-doped NaREF4 has been studied extensively, it is either for inefficient α-phase samples or for agglomerated β-phase ones. In this work, β-NaLuF4:Gd, Yb, Er submicron particles with efficient UCL were synthesized first by a facile solvothermal route, and then were coated with agglomeration-blocking SiO2 shell by a modified Stöber procedure, last UCL of the core@shell particles after different annealing treatments was studied, and we found large increase of red-to-green intensity ratio (R/G) up to 42 after annealing at 400 °C for 8 h, accompanying with significant shortening of decay time of the red UCL. Relationship between particles’ UCL and structure changes after annealing treatment was investigated in detail using in-situ spectroscopic measurement, in combination with in-situ temperature-change x-ray diffraction measurement. The initial increase of intensity for particles after annealing below 350 °C was ascribed to the crystal refinement of the particle cores; as the annealing temperature increase to between 350 and 400 °C, nearly single-band red UCL is achieved due to the particle cores gradual transition from single crystal to many much smaller poly-crystals accompanying with shortening of Er3+–Er3+ distance, indicated by the appearance of nano-pores; as the annealing temperature increases further, UCL weakens rapidly because of phase transition from hexagonal to cubic phases in the center area of the particle core and transition from crystalline phase to amorphous phase around the periphery of the core. In addition, the SiO2 shell coated on particles’ surface is able to prevent particles from agglomeration and delay the phase transition from hexagonal to cubic phases.

Microstructural formation and characterization mechanisms of selective laser melted Al–Si–Mg alloys with increasing magnesium content

We elucidated the microstructural formation and characterization mechanisms of Al–4Si–Mg selective laser melted (SLM) specimens with increasing Mg content (~2.5 mass%). First, the effect of Mg content on the processability of Al–4Si–Mg SLM specimens was systematically studied. From Al–4Si to Al–4Si–2.0Mg alloys, densified SLM specimens with a relative density of more than 99.5% were achieved by optimizing scan conditions. The relative density of the Al–4Si–2.5Mg SLM specimen decreased to approximately 99.4% due to the generation of gas pores by Mg evaporation. Then, the relation between the metal structures and mechanical properties and thermal conductivity of the Al–4Si–Mg SLM specimens was investigated. The tensile strength and 0.2% proof stress of the Al–4Si–Mg SLM specimens significantly increased with the Mg content. A multiscale metal structural analysis of the Al–4Si–Mg SLM specimens revealed that this strengthening was ascribed to multiple factors: both the crystal grain refinement and increase of solid-solute Mg in the α-Al matrix obstructed the dislocation movement. On the other hand, the elongation decreased in a stepwise manner with increasing Mg content. The SEM observations of the fracture surfaces in the Al–4Si–Mg tensile SLM specimens indicated that the decrease in elongation was attributed to the gas pores generated by Mg evaporation and shrinkage cavities. The thermal conductivity decreased slightly as the solid-solute Mg in the α-Al increased. These results can provide profound knowledge for the design of novel Al SLM alloys.

Structural and Thermoelectric Properties of Cu Substituted Type I Clathrates Ba₈CuxSi~32-xGa~14.

With an attempt to improve the thermoelectric properties of type I clathrates in the Ba-Ga-Si system, we introduce Cu into the framework of the crystal structure. Single crystals are prepared in Ga-flux and characterized by X-ray diffraction techniques and transport measurements for the structural and thermoelectric properties. Our composition analyses show that only a small amount of Cu is determined in the clathrates. The single crystal X-ray diffraction data refinements confirm that Ga atoms prefer the 6c and 24k sites and avoid the 16i sites in the crystal structure. The small amount of Cu affects the crystal structure by compressing the tetrakaidecahedral cage along the direction perpendicular to the six-atom-ring plane. This could be the reason for the high charge carrier concentration, and low electrical resistivity and Seebeck coefficient. We analyze the principal mechanism for our observation and conclude that the Cu substitution can adjust some subtle details of the structure, maintaining the Zintl rule in the type I clathrates.

Synthesis and investigation into the structural, electronic and electrical properties of K2Pb(OCN)I3.

Yellow transparent single crystals of the new compound K2Pb(OCN)I3 were synthesized from a mixture of lead iodide and potassium cyanate through a solid-state reaction, which was controlled by the differential scanning calorimetry (DSC) technique. The single crystal X-ray refinement showed that K2Pb(OCN)I3 crystallizes in the cubic system (Fd3[combining macron]m, a = 16.295(2) Å, V = 4327(1) Å3, Z = 16 and R1 = 0.0167). The structure is basically composed of two frameworks built from potassium tetrahedra capped by OCN- units and corner-sharing lead iodide octahedra. The infrared spectrum of K2Pb(OCN)I3 reveals the presence of vibration modes that were assigned to cyanate ions. The band structure and total and partial density of states calculated by DFT with the PBE functional (CASTEP code) showed that this compound exhibits a direct band gap of 2.19 eV, which is in good agreement with the experimental value obtained from a diffuse reflectance measurement (2.4 eV). The investigation of the electrical properties of this material demonstrates that it is highly resistive and has large permittivity (relative values of up to 104 at 150 °C). However, it does not display ferroelectric behavior.