Im3m Structure Research Articles

Aspects of strong electron–phonon coupling in superconductivity of compressed metal hydrides MH6 (M = Mg, Ca, Sc, Y) with Im-3m structure

Recently, YH6 was the first to be synthesized of the theoretically predicted stable compressed MH6 hydrides with bcc Im-3m crystal structures. Superconductivity of pressurized YH6 was confirmed, with a critical temperature (Tc) considerably lower than the value predicted by the Migdal–Eliashberg (ME) theory. Here, we present a theoretical re-investigation of the superconductivity of selected MH6 hydrides. Our results confirm that YH6 and ScH6 with Im-3m structure, at the requisite GPa pressures, are superconductors but with an anti-adiabatic character of the superconducting ground state and a multiple-gap structure in the one-particle spectrum. The transition into the superconducting state is driven by strong electron–phonon coupling with phonons of H atom vibrations. Based on the anti-adiabatic theory, the calculated critical temperature Tc in YH6 is ≈231 K, i.e., just ≈7 K higher than the experimental value. For ScH6, the calculated critical temperature is Tc ≈ 196 K. This value is 27 K higher than the former theoretical prediction. There are unexpected results for CaH6 and MgH6 in the Im-3m structure at necessary GPa pressures. The calculated band structures (BSs) indicate that in CaH6 and MgH6, the couplings to H stretching vibrations do not induce transitions into the superconducting anti-adiabatic state, and these hydrides remain stable in an adiabatic metal-like state, which contradicts former predictions of the ME theory. These discrepancies are discussed in association with the BS structures and the possible role of d-orbitals on the involved metals, in which we stress that the anti-adiabatic theory uses the BS topology and its stability as a key input.

Bacterial lipase triggers the release of antibiotics from digestible liquid crystal nanoparticles

In the advent of the post-antibiotic era, new strategies are urgently required to improve the efficacy of antimicrobials and outsmart multi-drug resistant bacteria. Exploiting a basic survival mechanism of bacteria, lipase production, monoolein liquid crystal nanoparticles (MO-LCNPs) were investigated as a bacterial-triggered drug delivery system for three different antimicrobial compounds and compared with model sn-1/3 regiospecific and non-regiospecific lipases via pH-stat titration, proton nuclear magnetic resonance and in situ synchrotron small-angle X-ray scattering. The release of model hydrophobic (rifampicin) and macromolecular (alginate lyase) antimicrobials were triggered from MO-LCNPs at 82-fold and 7-fold higher rates (respectively) due to bacterial lipase digestion of MO-LCNPs, which could not be stimulated with a small hydrophilic antibiotic (ciprofloxacin HCl) or non-digestible, phytantriol-LCNPs. While sn-1/3 regiospecific lipase rapidly digested MO-LCNPs in a two-phase process, the single-phase digestion kinetics of the non-regiospecific lipase steadily digested the cubic Im3m structure and gave rise to lamellar structures that ultimately stimulated the triggered antibiotic release. Accordingly, MO-LCNPs have an application for localised Pseudomonas aeruginosa and Staphylococcus aureus infections that produce non-regiospecific lipases and for concentration-dependent antibiotics that have macromolecular (MW ~ 30 kDa) or hydrophobic (logP ~ 4) chemistries, as a triggered bolus release would be clinically efficacious for improved bacterial eradication.

Structural evolution and magnetic properties of high-entropy CuCrFeTiNi alloys prepared by high-energy ball milling and spark plasma sintering

A powder of equiatomic CuCrFeTiNi high-entropy alloy (HEA) was prepared by short-term (30 min) high-energy ball milling (HEBM). Our structural and chemical analysis showed that micron sized particles of bcc CuCrFeTiNi consisting of nanosized crystalline grains (∼6 nm) could be obtained after 30 min of HEBM. The influence of milling time (30 ÷ 240 min) on structural and magnetic transformations of CuCrFeTiNi powder mixture was investigated. The HEA powders were thermally stable up to 500°С based on DSC results. The HEA powder was subsequently consolidated by spark plasma sintering at 700 °C resulting in a consolidated bulk HEA with co-existing bcc and fcc phases. The as-milled CuCrFeTiNi powder blend contained a solid solution with bcc (Im3m) structure. Annealing at 600°С (t = 180 min) increased the crystallinity of the α-phase (bcc) and gave rise to formation of the γ-phase (fcc, Fm3m) whose amount grew with increasing dwell time. Between 800 and 1000°С, a tetragonal intermetallic σ-phase – most likely FeCr - appeared and subsequently vanished. At 1000°С, the final product was found to contain two solid solutions based on the γ-phase (fcc). The Vickers hardness HvHEBM = 7.7 GPa of the SPS consolidated CuCrFeTiNi alloy (milled for t = 180 min) was markedly higher than the one of SPS-produced ones without HEBM (Hv = 2.1 GPa). Paramagnetic behavior at room temperature with a small ferromagnetic contribution at low fields was observed for as-milled powder after 180 min of HEBM. A small magnetic hysteresis was observed at 5 K and 300 K with a coercive field of around 16 kA/m. Above 100 K, the inverse susceptibility of a HEA powder ball-milled for t = 240 min showed a clear paramagnetic response. The Curie temperature TC ∼50 K was found.

First-principles demonstration of superconductivity at 280 K in hydrogen sulfide with low phosphorus substitution

Recently BCS superconductivity at 203 K has been discovery in a highly compressed hydrogen sulfide. We use first-principles calculations to systematically examine the effects of partially substituting the chalcogen atoms on the superconductivity of hydrogen chalcogenides under high pressures. We find detailed trends of how the critical temperature changes with increasing the V-, VI- or VII-substitution rate, which highlight the key roles played by low atomic mass and by strong covalent metallicity. In particular, a possible record high critical temperature of 280 K is predicted in a stable H3S0.925P0.075 with the Im-3m structure under 250 GPa.

Pressure-induced metallization of dense (H₂S)₂H₂ with high-Tc superconductivity.

The high pressure structures, metallization, and superconductivity of recently synthesized H2-containing compounds (H2S)2H2 are elucidated by ab initio calculations. The ordered crystal structure with P1 symmetry is determined, supported by the good agreement between theoretical and experimental X-ray diffraction data, equation of states, and Raman spectra. The Cccm structure is favorable with partial hydrogen bond symmetrization above 37 GPa. Upon further compression, H2 molecules disappear and two intriguing metallic structures with R3m and Im-3m symmetries are reconstructive above 111 and 180 GPa, respectively. The predicted metallization pressure is 111 GPa, which is approximately one-third of the currently suggested metallization pressure of bulk molecular hydrogen. Application of the Allen-Dynes-modified McMillan equation for the Im-3m structure yields high Tc values of 191 K to 204 K at 200 GPa, which is among the highest values reported for H2-rich van der Waals compounds and MH3 type hydride thus far.

Synthesis of ordered mesoporous carbon films with a 3D pore structure and the electrochemical performance of electrochemical double layer capacitors

Ordered mesoporous carbon films with a 3D pore structure (COU-3) were synthesized by a soft-templating method using resorcinol (R)/formaldehyde (F) as a carbon source and Pluronic F127 as a template agent. The carbon films were prepared by a spin-coating technique. From the results of X-ray diffraction pattern, field emission scanning electron microscope and transmission electron microscope observation, the structure of the COU-3 film was determined to be an Im3m structure whose c-axis is oriented perpendicular to the film surface. The pores run in the directions both perpendicular and parallel to the film surface. The porous structure of the film is different from the ordered mesoporous carbon powders and thick films (COU-1 and COU-2) which were synthesized using the same precursor solution. In the preparation of the COU-3 films, the self-assembly and condensation of a RF-F127 composite immediately occurred during the spin-coating. In this process, the RF-F127 composites are arranged on a substrate surface and an ordered structure spreads from the substrate surface to an upper region. The electrochemical performance of electrochemical double layer capacitor was examined. The CV curves are flat and rectangular in shape, and did not change even at a high scan rate, indicating that the internal resistance in grain boundary and the contact resistance with the substrate can be ignored in the COU-3 film. Additionally, the COU-3 film shows good cycle stability after 250 cycles.

Catalytic ozone oxidation of benzene at low temperature over MnOx/Al-SBA-16 catalyst

The low-temperature catalytic ozone oxidation of benzene was investigated. In this study, Al-SBA-16 (Si/Al = 20) that has a three-dimensional cubic Im3m structure and a high specific surface area was used for catalytic ozone oxidation for the first time. Two different Mn precursors, i.e., Mn acetate and Mn nitrate, were used to synthesize Mn-impregnated Al-SBA-16 catalysts. The characteristics of these two catalysts were investigated by instrumental analyses using the Brunauer-Emmett-Teller method, X-ray diffraction, X-ray photoelectron spectroscopy, and temperature-programmed reduction. A higher catalytic activity was exhibited when Mn acetate was used as the Mn precursor, which is attributed to high Mn dispersion and a high degree of reduction of Mn oxides formed by Mn acetate than those formed by Mn nitrate.

Revisiting β-Casein as a Stabilizer for Lipid Liquid Crystalline Nanostructured Particles

Lipid liquid crystalline nanoparticles such as cubosomes and hexosomes have unique internal nanostructures that have shown great potential in drug and nutrient delivery applications. The triblock copolymer, Pluronic F127, is usually employed as a steric stabilizer in dispersions of lipid nanostructured particles. In this study, we investigated the formation, colloidal stability and internal nanostructure and morphology of glyceryl monooleate (GMO) and phytantriol (PHYT) cubosome dispersions on substituting β-casein with F127 in increasing proportion as the stabilizer. Internal structure and particle morphology were evaluated using small-angle X-ray scattering (SAXS) and cryo-transmission electron microscopy (cryo-TEM), while protein secondary structure was studied using synchrotron radiation circular dichroism (SRCD). The GMO cubosome dispersion stabilized by β-casein alone displayed a V(2) (Pn3m) phase structure and a V(2) to H(2) phase transition at 60 °C. In comparison, F127-stabilized GMO dispersion had a V(2) (Im3m) phase structure and the H(2) phase only appeared at higher temperature, that is, 70 °C. In the case of PHYT dispersions, only the V(2) (Pn3m) phase structure was observed irrespective of the type and concentration of stabilizers. However, β-casein-stabilized PHYT dispersion displayed a V(2) to H(2) to L(2) transition behavior upon heating, whereas F127-stabilized PHYT dispersion displayed only a direct V(2) to L(2) transition. The protein secondary structure was not disturbed by interaction with GMO or PHYT cubosomes. The results demonstrate that β-casein provides steric stabilization to dispersions of lipid nanostructured particles and avoids the transition to Im3m structure in GMO cubosomes, but also favors the formation of the H(2) phase, which has implications in drug formulation and delivery applications.

Influence of synthesis temperature on morphology of SBA-16 mesoporous materials with a three-dimensional pore system

Spherical particles of mesoporous silica SBA-16 with cubic Im3m structure were synthesized at low pH using Pluronic F127 as template and TEOS as silica source. The diameter of the spherical particles can be controlled in the range of 0.5–8 μm by varying synthesis temperature from 1 °C up to 40 °C. A sharp transition from large particle sizes at approximately 20 °C to smaller ones is observed when the temperature is increased. It is suggested that this morphology transition is due to a change in hydrolysis and condensation rate of the silica source and as a result the assembly of F127 micelles will differ. The SBA-16 samples were characterized using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen adsorption techniques.

Novel Chiral Effect That Produces the Anisotropy in 3D Structured Soft Material: Chirality-Driven Cubic−Tetragonal Liquid Crystal Phase Transition

The effect of chirality on the liquid crystal organization has been systematically investigated between (S,S)- and (R,R)-isomers of a dichiral azobenzene compound. The racemic mixture was found to show the cubic phase (Im3m), indicating that the studied compound shows the cubic structure without the effect of chirality. However, with increasing optical purity of the racemic mixture, the cubic (Im3m) structure changes into the tetragonal phases (I422 and I4(1)22), which have been known as the SmQ phases, via a chiral cubic phase (I432). This is the first example of "chirality-driven" cubic-tetragonal structural change observed in liquid crystal systems, which is experimental evidence showing the novel type of chiral effect that produces the anisotropy in the structures of soft materials. The emergence of the anisotropy, i.e., the cubic-tetragonal phase transformation, is also induced by means of photoinduced phase transition of the SmQ phases based on cis-trans photoisomerization of the azobenzene compounds.

Ru(salen)(NO)] complex encapsulated in mesoporous SBA-16 as catalyst for hydrogenation of ketones

Abstract SBA-16 mesoporous silica with cubic Im3m structure was synthesized using Pluronic F127 poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer (EO106PO70EO106) and it blends with Pluronic P123 triblock copolymer (EO20PO70EO20) as supramolecular templates. The resulting material was used for encapsulating [Ru(salen)(NO)] complex and used in the hydrogenation of ketones to the corresponding alcohols. The pore entrance size of SBA-16 was precisely tailored by silylation with diphenyldichlorosilane to trap [Ru(salen)(NO)] complex in the cage of SBA-16. Small angle XRD, N2 sorption measurements, UV–Vis and FT-IR analysis evidences the structural integrity of mesoporous silica as well as the complex.

Synthesis and characterization of Ti-SBA-16 ordered mesoporous silica composite

Ti-SBA-16 mesoporous silica with a cubic Im3m structure has been successfully synthesized through prehydrolysis of a silica precursor in the presence of a tri-block copolymer F127 under acidic condition. X-ray diffraction (XRD) shows that the highly ordered mesostructure was maintained even at the high loading of titanium up to 5.5 (bulk molar ratio SiO2/TiO2). UV–vis and Raman spectroscopy reveal that the titanium species was highly dispersed in the silica framework with tetrahedral coordinate and octahedral coordinate, respectively. N2-adsorption data exhibit that the BET surface, pore size and pore volume were maintained with an increase of titanium species loading for this cubic Im3m mesoporous composite. SEM image shows its amorphous morphology. The synthesis of mesoporous TiO2-containing SBA-16 composite with a cubic Im3m structure will open new applications for catalysts.

Roughness and pore structure control of ordered mesoporous silica films for the enhancement of electrical properties

Mesostructured silica films with a well-ordered Im3m structure and enhanced surface properties can be synthesized by means of cosolvent addition and the optimization of sol aging time. Mesostructured silica films fabricated using ethanol, a commercial solvent, result in wavy surface properties induced by the Marangoni effect irrespective of rotation speed during spin coating. In order to improve the surface roughness, we used an ethanol-acetone mixture as a solvent with a certain molar ratio. Wavy and rough films could be avoided when the acetone molar ratio was optimized. The simultaneous increase of unit cell size and thickness of the film was observed when the amount of cosolvent was increased. The unit cell was also enlarged with sol aging time, and well-ordered mesoporous silica films could be synthesized by controlling the silica sol aging. The dielectric property could be improved by means of cosolvent addition only after the development of a highly ordered mesoporous nature of the film by calcination. The leakage current of the mesoporous silica film could be reduced when the structural ordering and surface roughness were controlled.

Structure Elucidation of the Highly Active Titanosilicate Catalyst Ti‐YNU‐1

Three novel zeolites (M-IEZ-MWW, IEZ-FER and IEZ-CDO) have been successfully synthesised from the corresponding precursors. Structure characterisation of those materials was conducted by TEM. Our studies show that the structure of the new zeolites keeps identical layer to the corresponding known 3D zeolite, except for the distinct expansion of the layer spacing. Combining with results from XRD, N2 adsorption, IR and NMR, the expansion can be explained by the pillaring of T sites between the layers. Meanwhile, the intergrowth of 3D MWW and IEZ-MWW was observed in the Al-IEZ-MWW and Si-IEZ-MWW crystals, IEZ-CDO structure was found in the IEZ-FER crystals, and the intergrowth of CDO and new polymorph was observed in the CDS-1 crystal. Moreover, two new zeolites IM-5 and SSZ-57 were also studied by TEM. We found that the space group of IM-5 is non-centrosymmetrical, and in SSZ-57 the new structure with slightly larger c parameter was observed compared to MEL. Chiral mesoporous silica nanotube and chiral mesoporous carbon nanotube were aslo investigated by TEM. We found that the former was synthesised by hollowing out process and it possesses chiral mesopores in the wall, the latter was synthesised by templating and seeding method. Electron tomography was first applied to study the handedness of the chiral mesoporous nanotube. Furthermore, TEM studies verified that bifunctional mesoporous silica has a Fm-3m structure, and mesoporous carbon FDU-16 has a Im-3m structure.

Tailoring the Pore Structure of SBA-16 Silica Molecular Sieve through the Use of Copolymer Blends and Control of Synthesis Temperature and Time

SBA-16 mesoporous silicas with cubic Im3m structure were synthesized using Pluronic F127 poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide) triblock copolymer (EO106PO70EO106) and its blends with Pluronic P123 triblock copolymer (EO20PO70EO20) as supramolecular templates. The resulting materials were characterized using X-ray diffraction, transmission electron microscopy, and argon and nitrogen adsorption. Selected samples were also modified with series of organosilanes of gradually increasing sizes and the accessibility of the pore structure after the modification was assessed using argon adsorption, which allowed us to determine the diameter of entrances to the ordered mesopores. It was shown that the pore cage diameter in SBA-16 can be enlarged in a wide range not only by increasing the synthesis temperature and time, as previously known, but also by increasing the content of P123 copolymer in the polymer mixture. These three ways allowed us to synthesize SBA-16 with nominal mesopore diameters from ∼4.5 to 9 nm. Even more importantly, they were also suitable for the tailoring of the pore entrance diameter from ∼1 to at least 6 nm, although in this case, the effect of the copolymer mixture composition on the entrance size was relatively small. In the case of SBA-16 samples synthesized at low temperatures or short hydrothermal treatment times, there was evidence that the pore entrance size was as low as 0.4−0.7 nm, as argon atoms were capable of entering the pore structure, but trimethylchlorosilane appeared to be largely excluded from it. By varying the synthesis temperature, time, and template composition, SBA-16 samples with essentially the same mesopore cage diameter and with largely different pore entrance sizes were synthesized. The present work is a step forward in the synthesis of a mesoporous molecular sieve with independently tailored mesopore diameter and entrance size.

Ordered mesoporous silica with large cage-like pores: structural identification and pore connectivity design by controlling the synthesis temperature and time.

FDU-1 silicas with large cage-like pores (diameter about 10 nm) were synthesized under acidic conditions from tetraethyl orthosilicate in the presence of a poly(ethylene oxide)-poly(butylene oxide)-poly(ethylene oxide) triblock copolymer template B50-6600 (EO(39)BO(47)EO(39)). High-resolution transmission electron microscopy and small-angle X-ray scattering provided strong evidence that FDU-1 silica synthesized under typical conditions is a face-centered cubic Fm3m structure with 3-dimensional hexagonal intergrowth and is not a body-centered cubic Im3m structure, as originally reported. Samples synthesized in a wide range of conditions (initial temperatures from 298 to 353 K; hydrothermal treatment at 333-393 K) exhibited similar XRD patterns and their nitrogen adsorption isotherms indicated a good-quality cage-like pore structure. The examination of low-pressure nitrogen adsorption isotherms for FDU-1 samples, whose pore entrance diameters were evaluated using an independent method, allowed us to conclude that low-pressure adsorption was appreciably stronger for samples with smaller pore entrance sizes. This prompted us to examine low-pressure adsorption isotherms for a wide range of samples and led us to a conclusion that the FDU-1 pore entrance size can be systematically enlarged from about 1.3 nm (perhaps even lower) to at least 2.4 nm without an appreciable loss of uniformity by increasing the temperature of the hydrothermal treatment or the initial synthesis. Further enlargement of pore entrance size was achieved for sufficiently long hydrothermal treatment times at temperatures of 373 K or higher, as seen from the shape of nitrogen desorption isotherms. This allowed us to obtain samples with uniform pore sizes, high adsorption capacity, and with pore entrances enlarged so much that their size was similar to the size of the pore itself, resulting in a highly open porous structure. However, in the latter case, there was evidence that the pore entrance size distribution was quite broad.

Synthesis of Large-Pore Silica with Cage-Like Structure Using Sodium Silicate and Triblock Copolymer Template

Silicas with large (about 10 nm in diameter), uniform, cage-like pores were synthesized from sodium silicate and poly(ethylene oxide)−poly(butylene oxide)−poly(ethylene oxide) B50-6600 triblock copolymer template (EO39BO47EO39) under acidic conditions. The synthesis procedure was analogous to that reported by others for FDU-1 silica with highly ordered cubic Im3m structure, but in our study, an expensive tetraethyl orthosilicate (TEOS) was successfully replaced by cost-efficient sodium silicate. Adsorption and thermogravimetric properties of the silicas synthesized from sodium silicate were found to closely resemble those of FDU-1 silicas synthesized from TEOS, but the pore volumes and specific surface areas of the former were found to be lower in most cases. The uniform cage-like structures assembled from sodium silicate formed at room temperature and 318 K, but no ordered structure was obtained at 333 K, whereas in the case of TEOS, an ordered structure formed also at 333 K. The sample synthesized at ro...

Rheology and Structures of Aqueous Gels of Triblock(oxyethylene/oxybutylene/oxyethylene) Copolymers with Lengthy Oxyethylene Blocks

Four EBE copolymers (E = oxyethylene repeat unit, B = oxybutylene repeat unit) based on a B20 central block and end blocks ranging from 58 to 260 E units were studied. Rheological measurements (oscillatory and steady shear) were used to confirm gel boundaries (previously explored by a tube inversion method) and to determine storage and loss moduli (G‘ and G‘ ‘) and yield stresses (σy) for aqueous gels formed at copolymer concentrations below 20 wt %. The phase diagrams contained a region of hard gel (G‘ > G‘ ‘, high G‘ and σy), an extensive region of soft gel ((G‘ > G‘ ‘, low G‘ and σy), denoted 1, and a second region of soft gel at low temperatures, denoted 2. Small-angle X-ray scattering was used to probe the hard gel structure. Concentrated aqueous gels (20 wt %) had a body-centered cubic (bcc, Im3m) structure. The structure of dilute gels near to the hard gel boundary was not defined, although the Im3m and Pm3n cubic structures were eliminated. Depending on concentration, the soft gels were assigne...

An X-ray diffraction study of the crystal structures of hexamethylethane and its phase transitions

We have examined the Im3m α-phase of hexamethylethane and low temperature phases β and δ, by Bragg and diffuse X-ray scattering. The Im3m phase fits well to a four thermal-parameter model at 188 and 295 K (R W = 12 per cent). The data suggest that significant improvement may come only from inclusion of intermolecular correlation between centre-of-molecular-mass and the orientation of neighbouring molecules' ethane axes. This results in a ‘static’ centre-of-mass positional disorder and a distribution in potential barriers to rotation about the molecular ethane axes. The β and metastable δ phases are tentatively identified as P21/c and P42/mnm, each derived from the Im3m structure by ordering of the molecular ethane axes, together with small distortions. The effect of crystal strain in stabilizing the δ-phase is discussed. Atom-atom intermolecular potentials are used to calculate the stabilities of various phases and the important correlations in the disordered Im3m phase.