The role of additives in a complex lithium silicate glass-ceramic

Several glass-ceramic compositions based on lithium silicates have been examined using thermal expansivity, X-ray diffraction, electrical conductivity, electron microscopy and solid state NMR studies. Role of P2O5 in nucleation and of Al2O3 in smoothening expansion behaviour have been particularly highlighted. Magic angle spinning NMR has been used to ascertain presence of Al in tetrahedral positions in the glassy phase

High pressure electrical measurements on Ge-Te-Se glasses

Electrical resistivity measurements have been carried out on bulk Ge-Te-Se glasses in a Bridgman anvil System. The resistivity of the Ge-Te-Se samples is found to decrease continuously with increasing pressure, with the metallization occurring around 8 GPa. Ge20TexSe80-x glasses (10 less than or equal to x less than or equal to 50) with the mean co-ordination number Z(av) = 2.4 exhibit a plateau in resistivity up to about 4 GPa pressure, followed by a continuous decrease to metallic values. On the other hand, Ge10TexSe90-x glasses (10 less than or equal to x less than or equal to 40) having Z(av) = 2.2, exhibit a smaller plateau (only up to 1 GPa), followed by a decrease in resistivity with pressure. This subtle difference in the high pressure resistivity of Ge-Te-Se glasses with Z(av) < 2.4 and Z(av) greater than or equal to 2.4 can be associated with the changes in the local structure of the chalcogenide glasses with composition.

Passivation of surface and bulk defects in p-GaSb by hydrogenated amorphous silicon treatment

Passivation of point and extended defects in GaSb has been observed as a result of hydrogenated amorphous silicon (a-Si:H) treatment by the glow discharge technique. Cathodoluminescence (CL) images recorded at various depths in the samples clearly show passivation of defects on the surface as well as in the bulk region. The passivation of various recombination centers in the bulk is attributed to the formation of hydrogen-impurity complexes by diffusion of hydrogen ions from the plasma a-Si:H acts as a protective cap layer and prevents surface degradation which is usually encountered by bare exposure to hydrogen plasma. An enhancement in luminescence intensity up to 20 times is seen due to the passivation of nonradiative recombination centers. The passivation efficiency is found to improve with an increase in a-Si:H deposition temperature. The relative passivation efficiency of donors and acceptors by hydrogen in undoped and Te-compensated p-GaSb has been evaluated by CL and by the temperature dependence of photoluminescence intensities. Most notably, effective passivation of minority dopants in tellurium compensated p-GaSb is evidenced for the first time. (C) 1996 American Institute of Physics.

Repeated drop weight impacts and post-impact ILSS tests on glass-epoxy composite

E glass epoxy laminates of thicknesses in the range 2-5 mm were subjected to repeated impacts. For each thickness the number of hits to cause tup penetration was determined and the value of this number was higher the larger the thickness of the laminate tested. The C-scan, before and after impact, was done to obtain information regarding flaw distribution. Short beam shear test samples were made from locations at fixed distances from impact point and tested. The samples closer to the zone of impact showed lower strength values. Scanning fractography revealed shear deformation features for these samples and brittle fracture features for the region near the zone of impact.

Differences in the glass-forming ability of rapidly solidified and mechanically alloyed Ti-Ni-Cu alloys

Melt spinning of Ti50Ni50 ? xCux (x = 10, 25, 40) alloys showed that the glass-forming ability is good for Cu-rich compositions and poor for Ni-rich compositions. The results of mechanical alloying experiments in the same system showed a reverse trend as far as the glass-forming ability is concerned. These contradictory results are explained in the light of thermodynamic and kinetic considerations. Crystallization results of the melt spun alloys are also presented.

Di- and tri-metallic complexes containing two bridging cyclodiphosphazane ligands: the crystal structure of [MO2(CO)8{µ-cis-[PhNP(OC6H4Me-p)]2}2]

The reactions of the mononuclear cyclodiphosphazane complexes, cis-[Mo(CO)(4){cis-[PhNP(OR)](2)}(2)] with [Mo(CO)(4)(nbd)] (nbd = norbornadiene). [Mo(CO)(4)(NHC5H10)(2)] or [MCl(2)(cod)] (cod = cycloocta-1,5-diene) afforded the homobimetallic complexes; [Mo-2(CO)(8){mu-cis-[PhNP(OR)](2)}(2)] (R = C(5)H(4)Me-p 5 or CH2CF3 6) or the heterobimetallic complexes. [Mo-2(CO)(8){mu-cis-[PhNP(OE)](2)}(2)MCl(2)] (R = C(6)H(4)Me-p; M = Pd 7 or Pt 8). In all the above complexes, the two metal moieties are bridged by two cyclodiphosphazane ligands. The reactions of the mononuclear complexes, cis-[M(CO)(4)(A){cis-[PhNP(OC(6)H(4)Me-p)](2)}] with (M'Cl-2(cod)] afforded the trinuclear complexes, cis-[M'Cl-2[M(CO)(4)(A){cis-[PhNP(OC(6)H(4)Me-p)](2)}](2)] (M' = Pd, M = Mo, A = P(OMe)(3) 10; M' = Pt, M = Mo. A = P(OMe)(3) 11; M' = Pd. M = W. A = NHC5H10 12; M' = Pt, M = W. A = NHC5H10 13). The structure of the complex 5 has been determined by single-crystal X-ray crystallography.

Study of fracture features in foam bearing glass epoxy composites subjected to repeated impacts

The paper reports the failure features observed in low mass repeatedly (pendulum) impacted glass epoxy composites with and without the mid section having either 2-layers or 3-layers of flexible foam. Features such as through width and inclined cracks as well as adhering of foam observed in the experiments are explained. The significance of the foam material in modifying the impact response of the composite is stressed.

Seebeck Coefficient in Bulk and Quantum Wells of Non-Parabolic Kane-Type Materials

We present a simplified and quantitative analysis of the Seebeck coefficient in degenerate bulk and quantum well materials whose conduction band electrons obey Kane's non-parabolic energy dispersion relation. We use k.p formalism to include the effect of the overlap function due to the band non-parabolicity in the Seebeck coefficient. We also address the key issues and the conditions in which the Seebeck coefficient in quantum wells should exhibit oscillatory dependency with the film thickness under the acoustic phonon and ionized impurity scattering. The effect of screening length in degenerate bulk and quantum wells has also been generalized for the determination of ionization scattering. The well-known expressions of the Seebeck coefficient in non-degenerate wide band gap materials for both bulk and quantum wells has been obtained as a special case and this provides an indirect proof of our generalized theoretical analysis.

Effect of wall emissivities on radiation heat transfer in glass tank forehearths

In an earlier work, we had proposed a two-band, non-grey radiative transfer model for heat transfer in forehearths with simultaneous optically thick and thin approximations for molten glass interiors and at boundaries. Here using the same model, the radiative interaction of the top-crown and bottom-refractory walls with interior layers of shallow molten glass is studied by varying the wall emissivities. The forehearth exit temperature profiles for higher wall emissivities (0.9) show better conditioning of the glass for white flint glasses (optically thin).

Low electric field, easily reversible electrical set and reset processes in a Ge15Te83Si2 glass for phase change memory applications

We report here an easily reversible set-reset process in a new Ge15Te83Si2 glass that could be a promising candidate for phase change random access memory applications. The I-V characteristics of the studied sample show a comparatively low threshold electric field (E-th) of 7.3 kV/cm. Distinct differences in the type of switching behavior are achieved by means of controlling the on state current. It enables the observation of a threshold type for less than 0.7 mA beyond memory type (set) switching. The set and reset processes have been achieved with a similar magnitude of 1 mA, and with a triangular current pulse for the set process and a short duration rectangular pulse of 10 msec width for the reset operation. Further, a self-resetting effect is seen in this material upon excitation with a saw-tooth/square pulse, and their response of leading and trailing edges are discussed. About 6.5 x 10(4) set-reset cycles have been undertaken without any damage to the device. (C) 2011 American Institute of Physics. doi: 10.1063/1.3574659]

Oriented films of LaNiO3 and other members of the Lan+1NinO3n+1 series, LaCuO3−δ and Pb(Zr0.52Ti0.48)O3, obtained by nebulized spray pyrolysis

The technique of nebulized spray pyrolysis has been explored to find out whether oriented films of certain important oxides can be produced on single-crystal substrates by this relatively gentle method. Starting with acetylacetonate precursors, oriented films of metallic LaNiO3 containing nearly spherical grains (30 nm) have been obtained. Films of near-stoichiometric La4Ni3O10 and La3Ni2O7 showing metallic conductivity have been obtained by this method. This is indeed gratifying since it is difficult to prepare monophasic and stoichiometric bulk samples of these materials. Films of La2NiO4 show the expected semiconducting behavior. In the La-Cu-O system, starting with acetylacetonates, we have obtained films mainly comprising semiconducting La2Cu2O5, which is generally difficult to prepare in bulk form. More interestingly, nebulized spray pyrolysis gives excellent stoichiometric films of Pb(Zr0.52Ti0.48)O-3 consisting of nearly spherical grains (30 nm) which show ferroelectric behavior. The present investigation demonstrates that nebulized spray pyrolysis provides a useful and desirable route to deposite oriented films of complex oxide materials on single-crystal substrates.

Specific heat measurements on Ge-Se-In glasses

Bulk glasses of Ge(20)Se(80-x)ln(x) (O less than or equal to x less than or equal to 18) have been used for measurements of heat capacity at constant pressure (C-p) using a differential scanning calorimeter. These measurements reveal the chemical threshold in these glasses as a function of composition. The results are discussed in the light of microscopic phase separation in these glasses.