A comparison of different powder compaction processes adopted for synthesis of lead-free piezoelectric ceramics

Barium zirconium titanate, Ba(Zr_0.15Ti_0.85)O₃ nano-crystalline powders were synthesized using highenergy ball milling. The calcined powders were compacted adopting two different approachesviz. the conventional uniaxial pressing and cold-isostatic pressing (CIP) and the compactswere sintered at 1350 °C. Asingle phase perovskite structure was observed in both cases. BZT ceramics compacted usingCIP technique exhibited enhanced dielectric and ferroelectric properties compared toceramics compacted by uniaxial pressing. The polarization current peaks have been used inthis paper as an experimental evidence to prove the existence of ferroelectricity in theBZT ceramics under study. The peak polarization current was found to be ~700% higher in case of coldiso-statically compacted ceramics. Similarly electric field induces strain showed amaximum strain (S_max) of 0.08% at an electric fieldof 28 kV/cm. The dielectric and ferroelectric properties observed are comparable to singlecrystals of the same material.     

1,3,5-trinitro-1,3,5-triazine decomposition and chemisorption on Al(111) surface: first-principles molecular dynamics study

We have investigated the decomposition and chemisorption of a 1,3,5-trinitro-1,3,5-triazine (RDX) molecule on Al(111) surface using molecular dynamics simulations, in which interatomic forces are computed quantum mechanically in the framework of the density functional theory (DFT). The real-space DFT calculations are based on higher-order finite difference and norm-conserving pseudopotential methods. Strong attractive forces between oxygen and aluminum atoms break N-O and N-N bonds in the RDX and, subsequently, the dissociated oxygen atoms and NO molecules oxidize the Al surface. In addition to these Al surface-assisted decompositions, ring cleavage of the RDX molecule is also observed. These reactions occur spontaneously without potential barriers and result in the attachment of the rest of the RDX molecule to the surface. This opens up the possibility of coating Al nanoparticles with RDX molecules to avoid the detrimental effect of oxidation in high energy density material applications.     

Recent observational constraints on EoS parameters of a class of emergent Universe

New Sr-based Y-type nanocrystalline hexagonal ferrites with a nominal chemical composition of Sr ₂Mg ₂Fe ₁₂ O ₂₂ (Sr ₂Y) were prepared by autocombustion from mixtures of Sr(NO ₃) ₂, Mg(NO ₃) ₂?6H ₂O and Fe(NO ₃) ₃?9H ₂O. The newly prepared Sr ₂Y nanocrystalline particles were characterized by powder X-ray diffraction (XRD). A well crystalline phase of Sr ₂Y with hexagonal crystal structure was observed. Fourier transform infrared spectroscopy (FTIR) studies revealed the information about the positions of the ions and their bonds within the lattice structure of the Sr ₂Y. The chemical elements and their oxidation states in the Sr ₂Y hexaferrites were determined using X-ray photoelectron spectroscopy (XPS). The XRD, FTIR and XPS studies confirmed the formation of Sr ₂Mg ₂Fe ₁₂ O ₂₂ hexaferrites. The morphology and porosity of the prepared Sr ₂Y nanocrystalline Sr ₂Y hexaferrite particles were studied by field emission scanning electron microscopy. The magnetic properties of Sr ₂Y hexaferrites showed dependence on the methods of preparation conditions and calcination treatments. The values of coercivity, saturation magnetization and retentivity were in the range of 21.33–19.66 kA m ^?1, 42.44– 38.72 emu g ^?1 and 10.05–13.19 emu g ^?1 respectively.     

Effect of proton irradiation on electrical properties of a-As2S3

This paper reports the effect of proton irradiation on the electrical properties of a-As₂S₃ in the temperature range of 323–418 K and frequency range 0.1–100 kHz. The variation of transport property is studied with proton irradiation dose (1 × 10¹³ ions/cm² and 1 × 10¹⁵ ions/cm²). It has been observed that proton irradiation changes the dc conductivity (σ_dc), dc activation energy (ΔE_dc) and ac conductivity (σ_ac(ω)). The σ_dc and σ_ac(ω) increases with dose of proton irradiation. The value of frequency exponent (s) decreases with the temperature and irradiation dose. These results are explained in terms of change in density of defect states in these glasses.     

Spin-resolved correlations in the warm-dense homogeneous electron gas

We have studied spin-resolved correlations in the warm-dense homogeneous electron gas by determining the linear density and spin-density response functions, within the dynamical self-consistent mean-field theory of Singwi et al. The calculated spin-resolved pair-correlation function g _{σ σ′}(r) is compared with the recent restricted path-integral Monte Carlo (RPIMC) simulations due to Brown et al. [Phys. Rev. Lett. 110, 146405 (2013)], while interaction energy E _int and exchange-correlation free energy F _xc with the RPIMC and very recent ab initio quantum Monte Carlo (QMC) simulations by Dornheim et al. [Phys. Rev. Lett. 117, 156403 (2016)]. g _↑↓(r) is found to be in good agreement with the RPIMC data, while a mismatch is seen in g _↑↑(r) at small r where it becomes somewhat negative. As an interesting result, it is deduced that a non-monotonic T-dependence of g(0) is driven primarily by g _↑↓(0). Our results of E _int and F _xc exhibit an excellent agreement with the QMC study due to Dornheim et al., which deals with the finite-size correction quite accurately. We observe, however, a visible deviation of E _int from the RPIMC data for high densities (~8% at r _s = 1). Further, we have extended our study to the fully spin-polarized phase. Again, with the exception of high density region, we find a good agreement of E _int with the RPIMC data. This points to the need of settling the problem of finite-size correction in the spin-polarized phase also. Interestingly, we also find that the thermal effects tend to oppose spatial localization as well as spin polarization of electrons.     

Effect of antimony addition on the thermal and electrical-switching behavior of bulk Se-Te glasses

The thermal properties and electrical-switching behavior of semiconducting chalcogenide Sb_xSe_55−xTe₄₅ (2 ? x ? 9) glasses have been investigated by alternating differential scanning calorimetry and electrical-switching experiments, respectively. The addition of Sb is found to enhance the glass forming tendency and stability as revealed by the decrease in non-reversing enthalpy ΔH_nr, and an increase in the glass-transition width ΔT_g. Further, the glass-transition temperature of Sb_xSe_55−xTe₄₅ glasses, which is a measure of network connectivity, exhibits a subtle increase, suggesting a meager network growth with the addition of Sb. The crystallization temperature is also observed to increase with Sb content. The Sb_xSe_55−xTe₄₅ glasses (2 ? x ? 9) are found to exhibit memory type of electrical switching, which can be attributed to the polymeric nature of network and high devitrifying ability. The metallicity factor has been found to dominate over the network connectivity and rigidity in the compositional dependence of switching voltage, which shows a profound decrease with the addition of Sb.     

Molecular dynamics and structure-based virtual screening and identification of natural compounds as Wnt signaling modulators: possible therapeutics for Alzheimer’s disease

Molecular Diversity - Wnt signaling pathway is an evolutionarily conserved pathway responsible for neurogenesis, axon outgrowth, neuronal polarity, synapse formation, and maintenance....