Ab-initio study of electronic,optical, thermal,and transport properties of Cr4AlB6

Theoretical investigation of different physical parameters of Cr₄AlB₆ have been done within the framework of density functional theory. Cr₄AlB₆ is a no band gap material. Its Cr-3d states contributes the most at the Fermi level. Thermal properties are investigated using quasi-harmonic Debye model as implemented in Gibbs code for different values of pressure and temperature. Study of transport property suggests that its electrical conductivity increases nonlinearly with increase in temperature but the relative change in its value is very low whereas its thermal conductivity increases linearly with the increase in temperature and relative increase in thermal conductivity is very high. The behavior of Cr₄AlB₆ is anisotropic and property is ceramic. It has potential applications in making ceramic capacitors. Its reflectivity is high in low energy region. It suggests that material can be used as coating material for far-infrared radiation. Study of the transport property suggests that because of very high value of thermal conductivity, it can be used for heat sink applications.     

Reliability of flexible electrically conductive adhesives

Based on our previous work about electrically conductive adhesives (ECAs), a flexibilizer named 1,3‐propanediol bis (4‐aminobenzoate) was used to fabricate flexible ECAs (FECAs). ECAs, FECAs, and electronic devices connected by them were carried out the hot and humid aging test under constant humidity level of 85% relative humidity at 85 °C for 600 h. After aging, the bulk resistance change of ECAs was about 26%, that of FECAs was a little higher, about 29%. The contact resistance change of devices connected by ECAs and FECAs was very great, about 450% and 410%, respectively. The bonding area at connection interface between colloids and devices had delamination, even cracks. The delamination of ECAs was calculated about 60%, the average shear strength of ECAs was reduced about 45%, and those of FECAs were about 50% and 30%, respectively, so FECAs had a higher bonding stability in hot and humid environment. Copyright © 2012 John Wiley & Sons, Ltd.     

Assimilation of manganese metal ion doped hydroxyapatite by Co-Precipitation technique

Calcium phosphate mineral [HAp] is a vital ingredient in orthopaedics, dental and hard tissue applications in mammals. Since it can absorb a large number of impurities, the doped HAp has the potential for biomedical applications using its physical and structural properties. In this research, the Mn-doped HAp in which x calcium atoms are replaced by Mn (Ca_10-x Mn_x (PO₄)₆(OH)₂ where x = 0.2, 0.4, 0.6, 0.8 mol) is obtained by the co-precipitation method. The physical properties of Mn-doped HAp, such as average crystallite size and degree of crystalline, are determined through XRD studies. The peaks corresponding to the functional groups PO4^3?, CO, and OH of the samples are identified by FTIR studies. The impedance spectroscopy method helps in the investigation of electrical conductivity, and dielectric loss in the impedance spectra for various doping concentrations. The average molar ratio of HApMn is determined with the help of EDX. It was found that there is a decrease in the degrees of crystallization with the doping element concentration (Mn) in all the samples. The diffraction (hkl) indices are confirmed from the selected area electron diffraction (SAED) rings, and the morphological study of the samples using TEM confirms the shape as a rod-like structure. To conclude, the variation in the characteristics of HAp relies on the doping concentration of Mn.     

Mechanical Properties of Gel-Derived Materials

The mechanical behaviour of xerogels and aerogels is generally described in terms of brittle and elastic materials, like glasses or ceramics. The main difference compared to silica glass is the order of magnitude of the elastic and rupture moduli which are 10⁴ times lower. However, if this analogy is pertinent when gels are under a tension stress (bending test) they exhibit a more complicated response when the structure is submitted to a compressive stress. The network is linearly elastic under small strains, then exhibits yield followed by densification and plastic hardening. As a consequence of the plastic shrinkage it is possible to densify and stiffen the gel at room temperature. These opposite behaviours (elastic and plastic) are surprisingly related to the same two kinds of gel features: the silanol content and the pore volume. Both elastic modulus and plastic shrinkage depend strongly on the volume fraction of pores and on the condensation reaction between silanols. On the mechanical point of view (rupture modulus and toughness), it is shown that pores and silanols play also an important role. Pores can be considered as flaws in the terms of fracture mechanics and the flaw size, calculated from rupture strength and toughness is related to the pore size distribution. Different kinds of gels structure (fractal or not fractal) have been synthesized by a control of the different steps of transformation such as sintering and plastic compaction. The relationships between structural and the elastic properties are discussed in terms of the percolation theory and fractal structure.     

Typical superparamagnetism with improved electrical properties of nano modified bismuth ferrite multiferroic composites

Multiferroic composites with the chemical formula, (0.5) BiFeO₃ + (0.5) Ni_0.5Zn_0.5Fe₂O₄, in bulk and nano forms were synthesized by preparing bismuth ferrite (BiFeO₃ or BFO) in bulk (B) and nano (N) forms and nickel zinc ferrite (Ni_0.5Zn_0.5Fe₂O₄or NZFO) in nano form. Single phase BFO was synthesized using conventional solid-state reaction as well as sol-gel autocombustion methods and NZFO powders were prepared by using sol-gel autocombustion method, respectively. X-ray diffraction (XRD) studies reveal the existence of rhombohedrally distorted perovskite structure for BFO and cubic spinel phase for NZFO in single phase as well as composite samples. Microstructural studies and energy dispersive spectroscopy (EDS) data reveal the formation of grains, intergranular porosities and chemical purity of the synthesized samples. Dielectric and AC conductivity measurements confirm the existence of space charge polarization along with the small polaron model in these composites. Ferroelectric and magnetic studies show that there was a considerable enhancement in the ferroelectric and magnetic orders for the nano form of the BFO (N) + NZFO composite. The observed remnant polarization values 2.80388 & 7.75901 μC/cm², saturation magnetization values 37.96072 & 40.47491emu/gm for bulk BFO (B) + NZFO and nano BFO (N) + NZFO composites, respectively. Interestingly, both the samples exhibit superparamagnetic behaviour at room temperature with coercivities close to zero. This typical behaviour is attributed to the corresponding anisotropic contributions originated from the individual constituents. The observed variations in BFO (N) + NZFO sample attributed to the corresponding structural modifications brought about by the variations due to its size effect in the present work.     

Mechanical and Morphological Properties of Bio-Phenolic/Epoxy Polymer Blends

Polymer blends is a well-established and suitable method to produced new polymeric materials as compared to synthesis of a new polymer. The combination of two different types of polymers will produce a new and unique material, which has the attribute of both polymers. The aim of this work is to analyze mechanical and morphological properties of bio-phenolic/epoxy polymer blends to find the best formulation for future study. Bio-phenolic/epoxy polymer blends were fabricated using the hand lay-up method at different loading of bio-phenolic (5 wt%, 10 wt%, 15 wt%, 20 wt%, and 25 wt%) in the epoxy matrix whereas neat bio-phenolic and epoxy samples were also fabricated for comparison. Results indicated that mechanical properties were improved for bio-phenolic/epoxy polymer blends compared to neat epoxy and phenolic. In addition, there is no sign of phase separation in polymer blends. The highest tensile, flexural, and impact strength was shown by P-20(biophenolic-20 wt% and Epoxy-80 wt%) whereas P-25 (biophenolic-25 wt% and Epoxy-75 wt%) has the highest tensile and flexural modulus. Based on the finding, it is concluded that P-20 shows better overall mechanical properties among the polymer blends. Based on this finding, the bio-phenolic/epoxy blend with 20 wt% will be used for further study on flax-reinforced bio-phenolic/epoxy polymer blends.     

The improvement of thermal stability and adhesion of silicone rubber composites modified by phenolic epoxy resin

The phenolic epoxy resin (F51) was siliconized by KH550 and the product was named as FKS. A hydroxyl-terminated polydimethylsiloxane (HTPDMS) which was modified with FKS was prepared. The siliconization reaction ensured a segment of siloxane on the side chain of F51. FT-IR and ¹H-NMR were employed to confirm the chemical structure of FKS. Morphology observations revealed that the enhancement of mechanical properties of the silicone rubber systems can be attributed to good compatibility between FKS and silicone rubber matrix. Thermogravimetric analysis showed that the residual yield at 800?°C of silicone rubber composites increased significantly when compared with that of neat HTPDMS. The mechanical properties demonstrated that tensile strength and elongation at break of silicone rubber system increased distinctly after modification, especially when 30 phr siliconized F51 were added to the silicone rubber. Shear strength was improved gradually with the addition of FKS. These above observations emphasize the vital effect of FKS on the behavior of modified HTPDMS.     

Effect of nano‐polystyrene (nPS) on thermal,rheological, and mechanical properties of polypropylene (PP)

Polystyrene nanoparticles (nPS) in the range of 10–100 nm with spherical shape were synthesized by oil/water (o/w) microemulsion process. In this process ammonium persulfate (APS) as an initiator, sodium dodecyl sulphate as a surfactant and n‐pentanol as cosurfactant were used. Isolated nPS was characterized by FTIR and ¹H NMR spectroscopy. DSC studies of nPS showed higher T_g as compared to bulk PS. The effect of lower weight percentage (wt%) of nPS on the mechanical, rheological, and thermal properties of PP was investigated. The blends were prepared individually on brabender plastograph by incorporating nPS of ～60 nm with different wt% of loading (i.e., 0.10–0.5%). It was shown from the experimental results that thermal, rheological, and mechanical properties were increased as the polymer particles blended with PP. Blends with 0.25 wt% loading of nPS exhibit better properties compared with that of other wt% loadings. The improvements in properties were due to the close packing of PP chains as recorded by improvement in crystallinity of PP with the addition of nPS as shown by SEM. Copyright © 2010 John Wiley & Sons, Ltd.     

Elastic, electronic and thermal properties of YSZ from first principles

First principles calculations were performed to investigate the elastic, electronic and thermal properties of 14% cubic yttria-stabilized zirconia (YSZ) using the pseudo potential plane-wave method within the gradient generalized approximation (GGA) for the exchange and correlation potential. Computed lattice constant parameters are in good agreement with the available experimental results. The three independent elastic constants were computed by means of the stress-strain method, indicating that 14% cubic YSZ is a mechanically stable structure. From the knowledge of the elastic constants, a set of related properties, namely bulk, shear modulus, Young’s modulus, sound velocity, Debye temperature, thermal capacity and minimum thermal conductivity are numerically estimated in the frame work of the Voigt-Reuss-Hill approximation for YSZ polycrystalline. The calculated bulk modulus, shear modulus, Young’s modulus, sound velocity, Debye temperature, thermal capacity and minimum thermal conductivity are in reasonable agreement with the available experimental and theory data. Density of states, charge density and Mulliken population analysis show that the 14% cubic YSZ is covalent and possess ionic character.     

Physical and excess properties of binary and ternary mixtures of 1,1-dimethylethoxy-butane, methanol, ethanol and water at 298.15 K

The ternary systems 1,1-dimethylethoxy-butane (BTBE) + methanol + water and BTBE + ethanol + water have large heterogeneous zones. Experimental densities, refractive indices and speeds of sound have been measured at 298.15 K for mixtures of these systems within the homogeneous zone, and also for methanol + BTBE and ethanol + BTBE binary systems over the entire range of compositions. Excess molar volumes and molar refraction and isentropic compressibility changes of mixing were calculated from the experimental physical properties and were satisfactorily correlated with the corresponding composition data using the Redlich-Kister polynomial. Fitted coefficients and mean standard deviations of correlations have been reported.     

Influence of crystal polymorphism on mechanical and barrier properties of poly(l-lactic acid)

The effect of crystal polymorphism on barrier and mechanical properties of PLLA is detailed in this contribution. PLLA films containing different amounts of α and α′ crystal forms were prepared by annealing quenched PLLA at different temperatures. The polymorphic structure of the films was analyzed by X-ray diffraction. Mechanical properties and permeability to water vapor were investigated as a function of degree of crystallinity (w_C) and related to crystal polymorphism developed during annealing. The polymorphic structure of PLLA significantly affects mechanical and barrier properties. The α crystal modification provides a better barrier to water vapor and a higher Young’s modulus, compared to films containing the α′ modification, but a lower elongation at break. The varied barrier and mechanical properties were correlated to the different packing of PLLA chains in the two analyzed polymorphs. The conformational disorder of the α′ form makes this structure a mesophase (condis crystal), with remarkable effects on material properties.     

Insight into the electronic,optical, thermodynamic,and thermoelectric properties of novel chalcogenides: An ab initio study

Ternary chalcogenides with direct band gaps are remarkable for being used in many optoelectronic applications. We investigated for structural, electronic, optical, and transport characteristics of new Ba₂CdCh₃ (Ch = S, Se, Te) semiconductors using the full-potential linearized augmented plane wave (FP-LAPW) approach. The band structures of these compounds confirm a direct type of band gap. The phonon dispersion plots along with the predicted negative formation energies suggest these compounds to be thermodynamically stable. Additionally, important optical characteristics were computed and thoroughly explained. The different ELF spectra were calculated in which strong peak correlate precisely with plasma resonance. Moreover, we also explored the thermodynamic characteristics of the ternary systems by employing the quasi-harmonic Debye model. These compounds were also suitable for thermoelectric applications based on the detailed discussion of the computed significant thermoelectric properties. In general, the advancement of various and promising semiconducting devices and their applications will be supported by the present study.     

Tough and transparent blends of polylactide with block copolymers of ethylene glycol and propylene glycol

In order to modify its physical properties, particularly the drawability and toughness, polylactide (PLA) was melt blended with a set of PEG-b-PPG-b-PEG block copolymers with varying ratio of the hydrophilic (PEG) and hydrophobic (PPG) blocks. Miscibility of the copolymers with PLA depended on their molar mass and PEG content. Interestingly, the best drawability was achieved in the case of partially miscible blends, in which fine liquid inclusions of the modifier were dispersed in PLA rich matrix with glass transition temperature only moderately decreased, to about 50 °C. About 37 fold increase of the elongation at break and about 1.5 fold increase of the tensile impact strength with respect to neat PLA were reached at small content (10 wt.%) of the modifier. Despite the phase separation, the blends remained transparent. In addition, the barrier properties for oxygen were improved.     

Synthesis and characterization of hyperbranched aromatic polyamide copolymers prepared from AB2 and AB monomers

A series of hyperbranched aromatic polyamide copolymers has been prepared and characterized from direct polycondensation of AB₂ and AB monomers. Structure of the monomers and the molar ratio of AB₂/AB showed strong influence on the properties of resulting copolymers. A small amount of AB₂ branching unit improved markedly the solubility of the resulting copolymer. Mark-Houwink parameters of the copolymers were essentially independent of the mole ratio of the monomers. The physical and mechanical properties of resulting copolymers were influenced not only by the mole ratio of monomers, but also by the structure of the monomers employed.     

Structural,mechanical, electronic,and thermodynamic properties of pure tungsten metal under different pressures: A first-principles study

The structural, mechanical, electronic, and thermodynamic properties of pure W metal under different pressures have been investigated using the first-principles method. Our calculated structural parameters are in good agreement with experimental and previous theoretical results. The obtained elastic constants show that pure W metal is mechanically stable. Elastic properties such as the bulk modulus (B), shear modulus (G), Young's modulus (E), Poisson's ratio (ν), Cauchy pressure (C′), and anisotropy coefficients (A) are calculated by the Voigt-Reuss-Hill method. The results show that the pressure can improve the strength of pure tungsten and has little effect on the ductility. In addition, the total density of states as a function of pressure is analyzed. Thermodynamic properties such as the Debye temperature, phonon dispersion spectrum, free energy, entropy, enthalpy, and heat capacity are also discussed.     

Thermal,structural and electrical properties

The chloro compound of 3-hydroxy-2-quinoxalinecarboxylic acid with nickel(II) has been prepared in ethanolic solution from which a solid compound was isolated. Spectral and magnetic measurements show that the nickel ions are in an octahedral environment. Thermogravimetry, differential thermal analysis and electrical conductivity data are reported for 3-hydroxy-2-quinoxalinecarboxylic acid and its nickel complex. The conductivity measurements indicate that electron/hole traps are emptied during heating of the complex but repopulation occurs in about 24 h at room temperature.     

Physical Properties of the Biodegradable Polymer Compositions Containing Natural Polyesters and their Synthetic Analogues

The thermal, mechanical and thermo-mechanical properties of polymer compositions, containing synthetic biodegradable polymers i.e. polylacide (PLA) and aliphatic-aromatic copolyester (BTA), natural biopolyester n-PHB and its synthetic atactic analog (a-PHB) were investigated. Thermal properties of the polymer compositions were studied by means of DSC . The compositions of various polymer weight ratio were tested. Compositions containing BTA and n-PHB create polyphase systems, what was confirmed by DSC. In this case the two Tg and two Tm values were observed. Polymer compositions containing PLA and BTA showed different behaviours. At the BTA content up to 30 weight % only one Tg and one Tm were indicated. At the increase of the BTA content to 50% weight and above, the two Tg, and two Tm were observed. Mixtures of BTA with n-PHB, PLA and with a-PHB show considerably greater values of the strain (ε) in comparison with initial polymers (n-PHB, PLA). It was found that in contrary to mixtures containing PLA, at the BTA content in the mixture with n-PHB above 50% of weights increases not only the strain, but also the stress at break (σ). Strong increase of the ε value in PLA/a-PHB mixtures with the content of a-PHB above 30% of weights were observed.     

Effect of chemical nature of atoms on the electronic,dielectric, and dynamical properties of ABX3 halide perovskite

First-principles calculations within density functional theory were performed on a series of halide perovskite compounds ABX₃(A: Cs or Rb; B:Pb or Sn). Their electronic structure, lattice dynamics, and dielectric properties were studied in relationship with the change in atom species at each one of the three inequivalent crystallographic sites, to explain the origin of these properties. Thus, the variation of the bandgap with the overlap between the B cation lone pair and the electronic states of halide atoms, as well as with the distortion of the BX₆ octahedra network is discussed. It is shown that the vibrational modes, phonon frequencies, atomic displacements, and the possible ferroelectric instability in these compounds are dependent on masses of atoms, volume of AX₁₂ polyhedron, as well as on streoactivity of Pb lone pair. Also, the Born effective charges, dielectric constant, spontaneous polarization, and infrared spectra are calculated. The relation between these dielectric properties and the ions dynamics is discussed.