Thermal anomalies in ternary Ge42-xPbxSe58 glasses near the charge carrier reversal threshold

The carrier type reversal (CTR) from p- to n-type in semiconducting chalcogenide glasses is an important and a long standing problem in glass science. Ge-Se glasses exhibit CTR when the metallic elements Bi and Pb are added. For example, bulk Ge42-xSe58Pbx glasses exhibit CTR around 8-9 at. % of Pb. These glasses have been prepared by melt quenching method. Glass transition temperature (T-g), Specific heat change between the liquid and the glassy states (Delta C-p) at T-g and the nonreversing heat flow (Delta H-nr) measured by modulated differential scanning calorimetry exhibit anomalies at 9 at. % of Pb. These observed anomalies are interpreted on the basis of the nano scale phase separation occurring in these glasses.

Low loss and frequency (1 kHz-1 MHz) independent dielectric characteristics of 3BaO-3TiO(2)-B2O3 glasses

X-ray powder diffraction along with differential thermal analysis carried out on the as-quenched samples in the 3BaO-3TiO(2)-B2O3 system confirmed their amorphous and glassy nature, respectively. The dielectric constants in the 1 kHz-1 MHz frequency range were measured as a function of temperature (323-748 K). The dielectric constant and loss were found to be frequency independent in the 323-473 K temperature range. The temperature coefficient of dielectric constant was estimated using Havinga's formula and found to be 16 ppm K-1. The electrical relaxation was rationalized using the electric modulus formalism. The dielectric constant and loss were 17 +/- 0.5 and 0.005 +/- 0.001, respectively at 323 K in the 1 kHz-1 MHz frequency range which may be of considerable interest to capacitor industry.

Surfactant-Mediated Synthesis of Functional Metal Oxide Nanostructures Via Microwave Irradiation-Assisted Chemical Synthesis

In the present work we report a rapid microwave irradiation-assisted chemical synthesis technique for the growth of nanoparticles, nanorods, and nanotubes of a variety of metal oxides in the presence of an appropriate surfactant (cationic, anionic, non ionic and polymeric), without the use of any templates. The method is simple, inexpensive, and helps one to prepare nanostructures in quick time, measured in seconds and minutes. This method has been applied successfully to synthesize nanostructures of a variety of binary and ternary metal oxides such as ZnO, CdO, Fe2O3, CuO, Ga2O3, Gd2O3, ZnFe2O4, etc. There is an observed variation in the morphology of the nanostructures with changes in different process parameters, such as microwave power, irradiation time, identity of solvent, type of surfactant, and its concentration.

Inducible nitric oxide synthase and control of intracellular bacterial pathogens

Inducible nitric oxide synthase (iNOS) has important functions in innate immunity and regulation of immune functions. Here, the role of iNOS in the pathogenesis of various intracellular bacterial infections is discussed. These pathogens have also evolved a broad array of strategies to repair damage by reactive nitrogen intermediates, and to suppress or inhibit functions of iNOS.

Nitric Oxide Is Involved in Mycobacterium bovis Bacillus Calmette-Guerin-Activated Jagged1 and Notch1 Signaling.

Pathogenic mycobacteria have evolved unique strategies to survive within the hostile environment of macrophages. Modulation of key signaling cascades by NO, generated by the host during infection, assumes critical importance in overall cell-fate decisions. We show that NO is a critical factor in Mycobacterium bovis bacillus Calmette-Guérin-mediated Notch1 activation, as the generation of activated Notch1 or expression of Notch1 target genes matrix metalloproteinase-9 (MMP-9) or Hes1 was abrogated in macrophages derived from inducible NO synthase (iNOS) knockout (iNOS(-/-)), but not from wild-type, mice. Interestingly, expression of the Notch1 ligand Jagged1 was compromised in M. bovis bacillus Calmette-Guérin-stimulated iNOS(-/-) macrophages, and loss of Jagged1 expression or Notch1 signaling could be rescued by NO donors. Signaling perturbations or genetic approaches implicated that robust expression of MMP-9 or Hes1 required synergy and cross talk between TLR2 and canonical Notch1-PI3K cascade. Further, CSL/RBP-Jk contributed to TLR2-mediated expression of MMP-9 or Hes1. Correlative evidence shows that, in a murine model for CNS tuberculosis, this mechanism operates in vivo only in brains derived from WT but not from iNOS(-/-) mice. Importantly, we demonstrate the activation of Notch1 signaling in vivo in granulomatous lesions in the brains of Mycobacterium tuberculosis-infected human patients with tuberculous meningitis. Current investigation identifies NO as a pathological link that modulates direct cooperation of TLR2 with Notch1-PI3K signaling or Jagged1 to regulate specific components of TLR2 responses. These findings provide new insights into mechanisms by which Notch1, TLR2, and NO signals are integrated in a cross talk that modulates a defined set of effector functions in macrophages.

High field electrical switching behavior of Ge10Se90-xTlx glasses

Electrical Switching Studies on bulk Ge10Se90-xTlx ( 15 <= x <= 34) glasses have been undertaken to examine the type of switching, composition and thickness dependence of switching voltages. Unlike Ge-Se-Tl thin films which exhibit memory switching, the bulk Ge10Se90-xTlx glasses are found to exhibit threshold type switching with fluctuations seen in their current-voltage (I-V) characteristics. Further, it is observed that the switching voltages (V-T) of Ge10Se90-xTlx glasses decrease with the increase in the Tl concentration. An effort has been made to understand the observed composition dependence on the basis of nature of bonding of Tl atoms and a decrease in the chemical disorder with composition. In addition. the network connectivity and metallicity factors also contribute for the observed decrease in the switching voltages of Ge10Se90-xTlx glasses with Tl addition. It is also interesting to note that the composition dependence of switching voltages of Ge10Se90-xTlx glasses exhibit a small Cusp around the composition x = 22. which is understood on the basis of a thermally reversing window in this system in the composition range 22 <= x <= 30. The thickness dependence of switching voltages has been found to provide an insight about the type of switching mechanism involved in these samples. (C) 2009 Elsevier B.V. All rights reserved

Oxide Particle Surface Chemistry and Ion Transport in "Soggy Sand" Electrolytes

The crucial role of oxide surface chemical composition on ion transport in "soggy sand" electrolytes is discussed in a systematic manner. A prototype soggy sand electrolytic system comprising aerosil silica functionalized with various hydrophilic and hydrophobic moieties dispersed in lithium perchlorate-ethylene glycol solution was used for the study. Detailed rheology studies show that the attractive particle network in the case of the composite with unmodified aerosil silica (with surface silanol groups) is most favorable for percolation in ionic conductivity, as well as rendering the composite with beneficial elastic mechanical properties: Though weaker in strength compared to the composite with unmodified aerosil particles, attractive particle networks are also observed in composites of aerosil particles with surfaces partially substituted with hydrophobic groups. The percolation in ionic conductivity is, however, dependent on the size of the hydrophobic moiety. No spanning attractive particle network was formed for aerosil particles with surfaces modified with stronger hydrophilic groups (than silanol), and as a result, no percolation in ionic conductivity was observed. The composite with hydrophilic particles was a sol, contrary to gels obtained in the case of unmodified aerosil, and partially substituted with hydrophobic groups.

Dielectric anomaly in Li-doped zinc oxide thin films grown by sol-gel route

Sol-gel route was employed to grow polycrystalline thin films of Li-doped ZnO thin films (Zn1-xLixO, x=0.15). Polycrystalline films were obtained at a growth temperature of 400-500 degrees C. Ferroelectricity in Zn0.85Li0.15O was verified by examining the temperature variation of the real and imaginary parts of dielectric constant, and from the C-V measurements. The phase transition temperature was found to be 330 K. The room-temperature dielectric constant and dissipation factor were 15.5 and 0.09 respectively, at a frequency of 100 kHz. The films exhibited well-defined hysteresis loop, and the values of spontaneous polarization (P-s) and coercive field were 0.15 mu C/cm(2) and 20 kV/cm, respectively, confirming the presence of ferroelectricity.

The glass transition and crystallization kinetic studies on BaNaB9O15 glasses

Transparent glasses of BaNaB9O15 (BNBO) were fabricated via the conventional melt-quenching technique. The amorphous and the glassy nature of the as-quenched samples were, respectively, confirmed by x-ray powder diffraction and differential scanning calorimetry (DSC). The glass transition and crystallization parameters were evaluated under non-isothermal conditions using DSC. The correlation between the heating rate dependent glass transition and the crystallization temperatures was studied and the Kauzmann temperature was deduced for BNBO glass plates and powdered samples. The values of the Kauzmann temperature for the plates and powdered samples were 776 K and 768 K, respectively. An approximation- free method was used to evaluate the crystallization kinetic parameters for the BNBO glass samples. The effect of the sample thickness on the crystallization kinetics of BNBO glasses was also investigated.

Effect of indium doping on the electrical switching behaviour of Ge-Te glasses

Bulk Ge15Te85-xInx (1 <= x <= 11) series of glasses have been found to exhibit a threshold switching behaviour for an input current of 2 mA. An initial decrease is seen in the switching voltages (V-T) with the addition of indium, which is due to the higher metallicity of indium. An increase is seen in V-T above 3 at.% of indium, which proceeds until 8 at.%, with a change in slope (lower to higher) seen around 7 at.%. Beyond x = 8, a reversal in trend is exhibited in the variation of V-T, with a well-defined minimum around x = 9 at.%. Based on the composition dependence of V-T, it is proposed that Ge15Te85-xInx glasses exhibit an extended rigidity percolation threshold. The composition, x = 3, at which the V-T starts to increase and the composition, x = 7, at which a slope change is exhibited correspond to the onset and completion, respectively, of the extended stiffness transition. Thermal studies and photoconductivity e85-xInx glasses. In addition, the minimum seen in V-T at x = 9 is associated with the chemical threshold (CT) of this glassy system.

Effect of the addition of B2O3 and BaO-B2O3-SiO2 glasses on the microstructure and dielectric properties of giant dielectric constant material CaCu3Ti4O12

The effect of the addition of glassy phases on the microstructure and dielectric properties of CaCu3Ti4O12 (CCTO) ceramics was investigated. Both single-component (B2O3) and multi-cornponent (30wt% BaO-60wt% B2O3-10wt% SiO2 (BBS)) glass systems were chosen to study their effect on the density, microstructure and dielectric properties of CCTO. Addition of an optimum amount of B2O3 glass facilitated grain growth and an increase in dielectric constant. However, further increase in the B2O3 content resulted in its segregation at the grain boundaries associated with a reduction in the grain size. In contrast, BBS glass addition resulted in well-faceted grains and increase in the dielectric constant and decrease in the dielectric loss. An internal barrier layer capacitance (IBLC) model was invoked to correlate the dielectric constant with the grain size in these samples. (c) 2007 Elsevier Inc. All rights reserved.

Ion irradiation enhances the mechanical performance of metallic glasses

We demonstrate that irradiation may enhance the plasticity in metallic glasses by increasing the free-volume content via micropillar compression experiments on an ion-irradiated bulk metallic glass (BMG). Results show that irradiation decreases the flow stress and enhances the shear band formation by lowering the magnitude of stress serrations in plastic flow regime. These results highlight that amorphous alloys can mitigate the deleterious affects of severe ion irradiation as compared to their crystalline counterparts. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Spectroscopic investigations and luminescence spectra of Nd3+ and Dy3+ doped different phosphate glasses

Spectral properties of Nd3+ and Dy3+ ions in different phosphate glasses were studied and several spectroscopic parameters were reported. Covalency of rare-earth-oxygen bond was studied in these phosphate glass matrices with the variation of modifier in host glass matrix Using Judd-Ofelt intensity parameters (Omega(2), Omega(4) and Omega(6)), radiative transition probabilities (A) and radiative lifetimes (tau(R)) of certain excited states of Nd3+ and Dy3+ ions are estimated in these glass matrices. From the magnitudes of branching ratios (beta(R)) and integrated absorption cross-sections (Sigma), certain transitions of both the ions are identified for laser excitation. From the emission spectra, peak stimulated emission cross-sections (sigma(P)) are evaluated for the emission transitions observed in all these phosphate glass matrices for both Nd3+ and Dy3+ ions. (C) 2009 Elsevier B.V. All rights reserved.

Evidence for a thermally reversing window in bulk Ge-Te-Si glasses revealed by alternating differential scanning calorimetry

Experiments on Ge15Tc85-xSix glasses (2 <= x <= 12) using alternating differential scanning calorimetry (ADSC) indicate that these glasses exhibit one glass transition and two crystallization reactions upon heating. The glass transition temperature has been found to increase almost linearly with silicon content, in the entire composition tie-line. The first crystallization temperature (T-cl) exhibits an increase with silicon content for x<5; T-cl remains almost a constant in the composition range 5 < x <= 10 and it increases comparatively more sharply with silicon content thereafter. The specific heat change (Delta C-p) is found to decrease with an increase in silicon content, exhibiting a minimum at x=5 (average coordination number, (r) = 2.4); a continuous increase is seen in Delta C-p with silicon concentration above x = 5. The effects seen in the variation with composition of T-cl and Delta C-p at x=5, are the specific signatures of the mean-field stiffness threshold at (r) = 2.4. Furthermore, a broad trough is seen in the enthalpy change (Delta H-NR), which is indicative of a thermally reversing window in Ge15Te85-xSix glasses in the composition range 2 <= x <= 6 (2.34 <= (r) <= 2.42).

Electrical switching and thermal studies on Ge22Te78-xIx chalcohalide glasses: The effect of iodine on network-topology

Investigations on the electrical switching behavior and thermal studies using Alternating Differential Scanning Calorimetry have been undertaken on bulk, melt-quenched Ge22Te78-,Is (3 <= x <= 10) chalcohalide glasses. All the glasses studied have been found to exhibit memory-type electrical switching. The threshold voltages of Ge22Te78-I-x(x) glasses have been found to increase with the addition of iodine and the composition dependence of threshold voltages of Ge22Te78-xIx glasses exhibits a cusp at 5 at.% of iodine. Also, the variation with composition of the glass transition temperature (Tg) of Ge22Te78-I-x(x) glasses, exhibits a broad hump around this composition. Based on the present results, the composition x = 5 has been identified as the inverse rigidity percolation threshold at which Ge22Te78-I-x(x) glassy system exhibits a change from a stressed rigid amorphous solid to a flexible polymeric glass. Further, a sharp minimum is seen in the composition dependence of non-reversing enthalpy (Delta H-nr) of Ge22Te78-I-x(x) glasses at x = 5, which is suggestive of a thermally reversing window at this composition. (C) 2007 Elsevier Ltd. All rights reserved.