Superconductivity, structure visualization, mechanical strength promotion and Raman spectra of hafnium-doped-123-YBCO synthesized via urea precursor route

The pure YBCO (YBa₂Cu₃O₇) and its variant hafnium containing superconductors with general formula: Y_1−xHf_xBa₂Cu₃O_z, where x = 0.1, 0.2, and 0.4 mole, respectively, were synthesized by solution route using urea as precursor forming agent. X-ray measurements indicated that Hf⁴⁺ ions have a negligible effect on the main crystalline structure and substitute Y-sites successfully in lattice structure of 123-YBCO at low levels of hafnium doping (x = 0.1 → 0.2 mole). From SE-microscopy mapping and EDX elemental analysis Hf⁴⁺ was detected qualitatively with good approximation to the actual molar ratio but not observed at 123-YBCO grain boundaries which confirm that hafnium (IV) has diffused regularly into material bulk of superconducting 123-YBCO-phase at low levels of concentrations. Structure visualization of Hf-doped-123-YBCO was made to confirm success of hafnium substitutions inside crystal lattice on Y-sites of 123-YBCO superconductors. Hafnium dopings affected sharply on the main vibrating modes of YBCO regime particularly on the apical oxygen (O₄) vibrational mode A₁g. Magnetic susceptibility measurements proved that hafnium dopings have strong effect on the transport properties of YBCO-composites regime. Hafnium promotes mechanical tensile coefficient recording maxima 35.7 MPa for x = 0.4 mole.     

Asymmetric Block Copolymers for Supramolecular Templating of Inorganic Nanospace Materials

This review focuses on polymeric micelles consisting of asymmetric block copolymers as designed templates for several inorganic nanospace materials with a wide variety of compositions. The presence of chemically distinct domains of asymmetric triblock and diblock copolymers provide self‐assemblies with more diverse morphological and functional features than those constructed by EO_nPO_mEO_n type symmetric triblock copolymers, thereby affording well‐designed nanospace materials. This strategy can produce unprecedented nanospace materials, which are very difficult to prepare through other conventional organic templating approaches. Here, the recent development on the synthesis of inorganic nanospace materials are mainly focused on, such as hollow spheres, tubes, and porous oxides, using asymmetric triblock copolymers.     

Thermal stability of hafnium silicate dielectric films deposited by a dual source liquid injection MOCVD

The hafnium and silicon precursors, Hf(NMe₂)₄ and Bu^tMe₂SiOH, have been investigated for the MOCVD of high- hafnium silicate, (HfO₂)_1–x –(SiO₂) _x films for gate dielectric applications. Control of the silica concentration in the hafnium silicate can be achieved by varying the relative precursor ratios up to a saturation level of 35–40% SiO₂. The thermal stability of the resulting hafnium silicate films in air has been investigated using medium energy ion scattering. Internal oxidation of the underlying silicon substrate is discernable when the films are annealed in dry air for 15 min over the temperature range 800–1000 °C.     

Effect of HfN Microadditions on the Microstructure and Superconducting Properties of (Bi,Pb)2Sr2Ca2Cu3O10 + x Ceramics

The effect of ultrafine hafnium nitride additions (0.05–0.2 wt %) on the microstructure, phase composition, density, and superconducting properties (T _c and j _c) of (Bi,Pb)₂Sr₂Ca₂Cu₃O_{10 + x} ceramics is studied. The elemental composition of individual phases is determined, and the magnetic-field distribution in the ceramics is examined. The introduction of hafnium nitride increases the density of the ceramics and improves their microstructural stability at sintering temperatures between 840 and 850°. The low hafnium solubility in the superconductor offers the possibility of attaining higher magnetizations and 77-K critical current densities.     

Study of impregnation of poly(l-lactide-ran-ε-caprolactone) copolymers with useful compounds in supercritical carbon dioxide

Outstanding controlled release materials were developed using statistically random copolymers of l-lactide (l-LA) with ε-caprolactone (CL) using Sn(oct)₂ as a catalyst at 150 °C for 24 h without solvent. Preparation of novel controlled release materials was carried out using useful organic compounds with low boiling points and synthetic random copolymers composed of l-LA and CL as base materials under supercritical carbon dioxide (scCO₂). Low-boiling-point compounds such as d-limonene, hinokitiol, and trans-2-hexenal were used. In impregnation experiments using scCO₂, the amounts of low-boiling-point compounds increased with an increase in l-LA content. When enzymatic degradation of poly(l-LA-ran-CL) was performed using lipase PS, copolymers with higher CL contents degraded more rapidly than did copolymers with higher l-LA content. In contrast, enzymatic degradation of copolymers occurred to a higher degree with increased l-LA content in enzymatic degradation by proteinase K. In a controlled release experiment with poly(l-LA-ran-CL) (=73/27), after 400 h of degradation by proteinase K, the remaining weight of the copolymer pellet was 6% and the amount of d-limonene remaining in the pellet was 15%.     

Narrow Range of Hafnium Doping for Promoted Mechanical Properties and Critical Current Density (Jc) Values of?Mg1?xHfxB2 Superconductor

Hafnium was used as a softener dopant to replace at magnesium sites of Mg_1−x Hf _x B₂ regime (where x=0.0, 0.05, 0.1, 0.2, and 0.4 mole). Samples were prepared via high temperature solid state reaction technique depending upon diffusion mechanism of Mg-vapor ions through hafnium–boron matrix. The maximum solubility limit of hafnium (n) was found to be ∼0.22 mole. The crystalline lattice constants exhibit slight elongation in the case of the c-axis as x increases. Furthermore, the effect of Hf-doping on the microstructure properties of the MgB₂ system was investigated carefully. The SE-microscopic analysis indicated that hafnium ions diffuse regularly through surface and bulk in case of (x=0.05–0.2 mole). The grain size was estimated and found to be between 0.33 and 1.34 μm. The mechanical tensile strength of the samples was clearly improved linearly as Hf-content increased, recording the maximum tensile strength of 34.8 MPa for the sample with x=0.4 mole. A visualization of the Hf-doped MgB₂ structure was constructed and investigated to confirm the success of hafnium substitutions at the Mg-sites of the MgB₂ superconductor.     

Dithiopheneindenofluorene (TIF) Semiconducting Polymers with Very High Mobility in Field‐Effect Transistors

The charge‐carrier mobility of organic semiconducting polymers is known to be enhanced when the energetic disorder of the polymer is minimized. Fused, planar aromatic ring structures contribute to reducing the polymer conformational disorder, as demonstrated by polymers containing the indacenodithiophene ( IDT ) repeat unit, which have both a low Urbach energy and a high mobility in thin‐film‐transistor (TFT) devices. Expanding on this design motif, copolymers containing the dithiopheneindenofluorene repeat unit are synthesized, which extends the fused aromatic structure with two additional phenyl rings, further rigidifying the polymer backbone. A range of copolymers are prepared and their electrical properties and thin‐film morphology evaluated, with the co ‐benzothiadiazole polymer having a twofold increase in hole mobility when compared to the IDT analog, reaching values of almost 3 cm² V^?1 s^?1 in bottom‐gate top‐contact organic field‐effect transistors.     

Oligomer semiconductor/dielectric interface modification for organic thin film transistor hysteresis reduction

In this work, we investigate the hydroxyl group effect on hysteresis of the low voltage organic thin film transistor (OTFT). A high k material, hafnium oxide, is utilized as gate dielectric to reduce OTFT operational voltage. By using the hydroxyl-free polymer, polystyrene, the hydroxyl groups on hafnium oxide surface will be shielded. The modification at semiconductor/dielectric interface prevents accumulated charges from trapping in surface states. Such a polymer coverage layer reduces hysteresis and suppresses the off current as low as 10⁻¹¹ A. The interface traps resulted from ambient water absorption significantly decrease according to the hysteresis cancellation. By stacking polystyrene on hafnium oxide, the pentacene-based OTFT shows the threshold voltage of − 2.2 V, on/off current ratio of 10⁵, subthreshold swing of 0.34 V/dec, and mobility of 0.24 cm²/V s under operational voltage of 10 V.     

Segregation of reactive elements at oxide grain boundaries in FeCrAlRE alloys

Abstract

Extensive previous research has established that the oxidation of FeCrAl alloys at temperatures ≥1000°C results in the formation of α-Al₂O₃ oxide scales, and that minor alloy constituents (particularly Reactive Elements (RE) such as Y, Hf, Zr, etc.) can change the oxide growth mechanism. A knowledge of the segregation behaviour of these REs is thus central to our understanding of the oxidation behaviour of these, technologically important, range of alloys.

The new SuperSTEM microscope at the Daresbury Laboratory offers considerable potential for a detailed study of the segregation to oxide grain boundaries at the atomic level. The microscope has an aberration corrector fitted to the objective lens, allowing the formation of sub-Angstrom probe for simultaneous ultra-high resolution high angle annular dark field (HAADF) imaging and atomic-column electron energy loss spectroscopy (EELS). This paper reports on an initial study of oxide grain boundary segregation in commercial and model FeCrAlRE alloys containing controlled additions of the reactive elements, yttrium, zirconium and hafnium oxidised at 1250°C, in air, for 50 hours. Both yttrium and hafnium are shown to segregate to the grain boundaries while hafnium rich particules form in the outer region of the scale.     

Thermal stability of hafnium silicate dielectric films deposited by a dual source liquid injection MOCVD

The hafnium and silicon precursors, Hf(NMe₂)₄ and Bu^tMe₂SiOH, have been investigated for the MOCVD of high-κ hafnium silicate, (HfO₂)_1–x –(SiO₂) _x films for gate dielectric applications. Control of the silica concentration in the hafnium silicate can be achieved by varying the relative precursor ratios up to a saturation level of 35–40% SiO₂. The thermal stability of the resulting hafnium silicate films in air has been investigated using medium energy ion scattering. Internal oxidation of the underlying silicon substrate is discernable when the films are annealed in dry air for 15 min over the temperature range 800–1000 °C.     

The effects of hydroxide gel drying on the characteristics of co-precipitated zirconia-hafnia powders

Mixed zirconia-hafnia (Hf_0.25Zr_0.75O₂) powders of fine particle size and narrow particle-size distribution can be prepared via co-precipitation routes using mixed zirconium and hafnium salts as the starting materials. The characteristics of the resultant zirconia-hafnia powders are dependent strongly on the dehydration route by which the co-precipitated hydroxide gels are dried. Zirconium-hafnium hydroxide gels are formed when zirconium and hafnium oxynitrates are co-precipitated in an ammonia solution of pH 10.5. The co-precipitated hydrous gels were dried by three very different routes including organic solvent dehydration, microwave drying, and conventional infrared heating lamp drying. The dried hydroxides were then calcined at various temperatures in the temperature range 550–1150 °C, followed by ball milling to remove large soft-particle agglomerates. The resultant zirconia-hafnia powders were characterized for crystallite size, particle size, particle-size distribution, particle morphology, and the degree of powder agglomeration, using experimental techniques such as X-ray diffraction, BET surface area, differential thermal analysis, thermo-gravimetric analysis, sedigraph, scanning and transmission electron microscopy. Hard particle aggregates, which cannot be effectively eliminated using ball milling, occur in the zirconia-hafnia powders processed via either the microwave drying or conventional infrared heating lamp drying routes. In contrast, the organic solvent dehydration route resulted in an almost aggregate-free powder of fine crystallite and particle sizes. Therefore, the zirconia-hafnia powder processed via the organic solvent dehydration route exhibited high sinterability on sintering at 1300 °C.     

Synthesis,characterization, and antibacterial activities of novel <Emphasis Type="Italic">N</Emphasis>-halamine copolymers

The synthesis and antibacterial properties of N-halamine copolymers are reported in this paper. 3-(4′-vinylbenzyl)-5,5-dimethylhydantoin (VBDMH) monomer and its copolymers with n-butyl methacrylate (BMA) were prepared under mild conditions. The effects of monomer feeds on the composition of the final copolymers and reaction conversion were investigated. It was found that VBDMH had higher reactivities than BMA in the copolymerization reactions and the reactivity ratios of VBDMH and BMA were calculated to be 8.91 and 0.42, respectively, according to the Fineman–Ross equation in the preparation of PBMA-co-VBDMH. Two chlorination methods were applied and compared in the process of polymers chlorination. After chlorination by tert-butyl hypochlorite, the polymers provided powerful antibacterial activities against Escherichia coli (E. coli). The surface morphologies of the chlorinated polymer films used in antibacterial assessment were observed by scanning electron microscope. The copolymers before and after chlorination were characterized with fourier transform infrared (FTIR) and ¹H-nuclear magnetic resonance (¹H-NMR). Their thermal properties were analyzed with thermogravimetric analysis (TGA) studies.     

The structure solution of the F-type i-ZnMgHf from the X-ray diffraction

ABSTRACT

We report a successful growth of the ZnMgHf F-type icosahedral quasicrystal in the form of faceted single grains. By varying the heat treatment parameters we were able to obtain single crystals with a quality suitable for a single crystal X-ray diffraction which was conducted in a synchrotron facility. Ab initio structure solution by a charge flipping algorithm manifests the existence of two types of Bergman clusters. Clusters are differentiated by the preferential occupation of the high-symmetry positions by hafnium in a rhombic triacontahedron, being the outer shell of the atomic cluster.

This paper is part of a Thematic Issue on The Crystallographic Aspects of Metallic Alloys.     

Synthesis and Characterization of Methacrylic Derivatives as Drug Carriers

Abstract

p-Methoxyphenyl methacrylate (ESMAA) was copolymerized with methacrylic acid (MAA) in dioxane solutions using azobisisobutyronitrile (AIBN) as an initiator. The compositions of the copolymers were assayed for the aromatic ester content by measuring the ultraviolet (UV)absorbance at 240 nm in dioxane. The monomer reactivity ratios r₁and r₂ for copolymerization of MAA(M₁)and ESMAA (M₂)are 1.52 and 3.01. The glass transition temperatures of MAA-ESMAA copolymers are almost equal to the weight-average values. The drug released from copolymers increases with the composition of methacrylic acid units. The releases of piroxicam from the MAA-co-ESMAA matrices containing 55 mole%MAA in pH 7.4 and 10 buffer solutions are steady for the whole release period, and release profiles matches closely to the disintegration profiles of the MAA-55 copolymer.     

Superconducting current carrying capacities of the composite-processed Nb-Hf/Cu-Sn-Ga in high magnetic fields

The Nb₃Sn growth rate, H_c2, and J_c of composite processed Nb₃Sn are substantially increased by the addition of hafnium to the niobium core. Furthermore, simultaneous addition of hafnium to the core and gallium to the matrix significantly increases H_c2 and J_c in high magnetic fields. SEM observations indicate that the addition of hafnium to the core enhances the growth rate of the Nb₃Sn layer without increasing the grain size of Nb₃Sn while the addition of gallium to the matrix causes an increase in coarseness of Nb₃Sn grains. The XMA analysis indicates the presence of small amounts of gallium and hafnium in the Nb₃Sn layer, J_c of the Nb-Hf/Cu-Sn-Ga wire specimens exceeds 1 × 10⁵ A cm^?2 at 17 T, suggesting that multifilamentary Nb₃Sn composite wires capable of generating magnetic fields over 17 T may be feasible.     

Electrical conductivity of homopolymer and copolymers of <Emphasis Type="Italic">N</Emphasis>-vinylcarbazole

Poly(N-vinylcarbazole) (PVCz) is well known as an electroactive material due to its good photoconductivity, charge-transfer complexes, photoluminescence and electroluminescence properties. The block copolymers of N-vinylcarbazole were prepared and the effects of the relative composition, molar masses, architecture and doping on its electrical behavior were investigated. Controlled free radical polymerization has been carried out using nitroxide-mediated process in order to prepare a series of block copolymers of N-vinylcarbazole. 2,2,6,6-Tetramethyl-1-piperidinyloxy radical (TEMPO) was used to end-cap “living” homopolymer of p-bromostyrene, which was further used as a macroinitiator to polymerize N-vinylcarbazole and styrene. The copolymers have been doped at room temperature with LiClO₄ and the electrical conductivities were measured by two-probe method, which have shown to depend on copolymer’s relative composition and molar masses.     

Realizing Over 13% Efficiency in Green‐Solvent‐Processed Nonfullerene Organic Solar Cells Enabled by 1,3,4‐Thiadiazole‐Based Wide‐Bandgap Copolymers

Two novel wide‐bandgap copolymers, PBDT‐TDZ and PBDTS‐TDZ, are developed based on 1,3,4‐thiadiazole (TDZ) and benzo[1,2‐b:4,5‐b′]dithiophene (BDT) building blocks. These copolymers exhibit wide bandgaps over 2.07 eV and low‐lying highest occupied molecular orbital (HOMO) levels below −5.35 eV, which match well with the typical low‐bandgap acceptor of ITIC, resulting in a good complementary absorption from 300 to 900 nm and a low HOMO level offset (≤0.13 eV). Compared to PBDT‐TDZ, PBDTS‐TDZ with alkylthio side chains exhibits the stronger optical absorption, lower‐lying HOMO level, and higher crystallinity. By using a single green solvent of o‐xylene, PBDTS‐TDZ:ITIC devices exhibit a large open‐circuit voltage (V_oc) up to 1.10 eV and an extremely low energy loss (E_loss) of 0.48 eV. At the same time, the desirable high short‐circuit current density (J_sc) of 17.78 mA cm⁻² and fill factor of 65.4% are also obtained, giving rise to a high power conversion efficiency (PCE) of 12.80% without any additive and post‐treatment. When adopting a homotandem device architecture, the PCE is further improved to 13.35% (certified as 13.19%) with a much larger V_oc of 2.13 V, which is the best value for any type of homotandem organic solar cells reported so far.     

Micellar carrier based on methoxy poly(ethylene glycol)-block-poly(<Emphasis Type="Italic">ε</Emphasis>-caprolactone) block copolymers bearing ketone groups on the polyester block for doxorubicin delivery

Block copolymers of Methoxy poly(ethylene glycol)-block-poly(ε-caprolactone) bearing ketone groups (MPEG-b-P(CL-co-OPD)) are synthesized and evaluated for its potential to form micelles containing doxorubicin (DOX), a representative anticancer drug, by using an in vitro method based on membrane dialysis to emulate drug release in vivo. The ¹H NMR spectra of the prepared block copolymers in D₂O solution exhibit peaks due to the P(OPD-co-CL) in decreased intensity, indicates that the polymers form micelle particles containing the hydrophilic segments in their external parts. The CMC of the copolymer decrease with an increase in the content of ketone groups in the hydrophobic chain. Drug-free and drug-loaded solutions of structurally related copolymers indicate the polymeric aggregation into micellar-type constructs. The size of the drug-loaded micelles is found to be larger than corresponding drug-free micelles. The release rate of MPEG-b-PCL micelles is faster than MPEG-b-P(OPD-co-CL) micelles in pH 7.4 buffered solution and they have a similar release rate in pH 5.0 buffered solution. This study, therefore, confirms the potential of a novel functional block copolymers, Methoxy poly(ethylene glycol)-block-poly(ε-caprolactone) bearing ketone Groups, for the formation of polymeric micelles for drug delivery.     

Novel thieno[3,4-c]pyrrole-4,6-dione-based conjugated copolymers with donor–acceptor structures

A series of novel copolymers with alkylthiophene/alkoxythiophene and the thieno[3,4-c]pyrrole-4,6-dione moieties were synthesized by Sonogashira cross-coupling reactions. The structures and properties of these copolymers were characterized using FT–IR, ¹H NMR, UV–Vis, thermal gravimetric analysis, different scanning calorimetry, and cyclic voltammetry (CV). All of the copolymers possess adequate thermal stability, and exhibit good solubility in common organic solvents such as THF, chloroform, and toluene. The electrochemical and photophysical properties were investigated, and the results show that the spectral response of these copolymers are extended up to 700, 750, and 640 nm for P ₁ , P ₂ , and P ₃ , respectively. CV studies reveal that the band gaps of these copolymers range from 1.51 to 1.97 eV, implying that the resulted polymers may be promising candidates for solar cells.     

Conjugated Microporous Polymers

Conjugated microporous polymers are of great interest because they have potential to combine high surface areas in the dry state with physical properties relevant to organic electronics. A series of recent reports has shown that materials such as poly(aryleneethynylene)s (PAEs), poly(phenyl‐ene butadiynylene)s, poly(phenylene vinylene), poly(p‐phenylene)s, polysilanes, polyanilines, and polytriazines can be produced as microporous networks with apparent Brunauer–Emmett–Teller surface areas of more than 1000 m² g^?1 in some cases. Micropore size and surface area can be synthetically fine tuned in amorphous PAE polymers and copolymers, something which was previously thought to be the preserve of ordered crystalline materials such as metal organic frameworks. We review in this Research News article recent progress made by our group and others with particular emphasis on the possible future applications of these materials.