High-pressure studies on lithium fast-ion conductors

The variation of resistivity of the lithium fast-ion conductor Li3+y Ge1−yO4 (y = 0.25, 0.6, 0.72) has been studied with hydrostatic pressure up to 70 kbar and compared with that of Li16−2x Znx (GeO4)4(x = 1, 2). Both types showed pronounced resistivity maxima between 20–30 kbar and marked decrease thereafter. Measurements as a function of temperature between 120–300 K permitted the determination of activation energies and prefactors that also showed corresponding maxima. The activation volumes (ΔV) of the first type of compound varied between 4.34 to −4.90 cm3/mol at 300 K and decreased monotonically with increasing temperature. For the second type ΔV was much smaller, varied with pressure between 0.58 and −0.24 cm3/mol, and went through a maximum with increasing temperature. High-pressure studies were also conducted on aged samples, and the results are discussed in conjunction with results of impedance measurements and nuclear magnetic resonance (NMR) studies. The principal effect of pressure appears to be variations of the sum of interatomic potentials and hence barrier height, which also causes significant changes in entropy.

Properties of Al2O3 films prepared by argon ion assisted deposition

Aluminum oxide films have been prepared by ion assisted deposition using argon ions with energy in the range 300 to 1000 eV and current density in the range 50 to 220 μA/cm2. The influence of ion energy and current density on the optical and structural properties has been investigated. The refractive index, packing density, and extinction coefficient are found to be very sensitive to the ion beam parameters and substrate temperatures. The as-deposited films were found to be amorphous and could be transformed into crystalline phase on annealing. However, the crystalline phases were different in films prepared at ambient and elevated substrate temperatures.

Stresses in Ion Assisted Deposited Oxide Thih Films

Thin films of Ceria, Titania and Ziroonia have been prepared using Ion Assisted Deposition(IAD). The energy of ions was varied between 0 and 1 keV and current densities up to 220 μA/cm were used. It was found that the stress behaviour is dependent on ion species, i.e. Argon or Oxygen, ion energy and current density and substrate temperature apart from the material. While oeria files showed tensile stresses under the influence of argon ion bombardment at ambient temperature, they showed a sharp transition from tensile to compressive stress with increase in substrate temperature. When bombarded with oxygen ions they showed a transition from tensile to compressive stress with increase in energy. The titania films deposited with oxygen ions, on the other hand showed purely tensile stresses. Zirconia films deposited with oxygen ions, however, showed a transition from tensile to compressive stress.

Superconductivity of embedded lead nano particles in metallic and amorphous matrices

Nanodispersed lead in metallic and amorphous matrices was synthesized by rapid solidification processing. The optimum microstructure was tailored to avoid percolation of the particles. With these embedded particles it is possible to study quantitatively the effect of size on the superconducting transition temperature by carrying out quantitative microstructural characterization and magnetic measurements. Our results suggest the role of the matrices in enhancement or depression of superconducting transition temperature of lead. The origin of this difference in behavior with respect to different matrices and sizes is discussed.

Structural Relaxation and Crystallization in a Pd40Cu30Ni10P20 Bulk Metallic Glass

The stability of a Pd40Cu30Ni10P20 bulk metallic glass (BMG) against structural relaxation is investigated by isothermal and isochronal annealing heat treatments below and above its glass transition temperature, Tg, for varying periods. Differential scanning calorimetry (DSC) of the annealed samples shows an excess endotherm at Tg, irrespective of the annealing temperature. This recovery peak evolves exponentially with annealing time and is due to the destruction of anneal-induced compositional short range ordering. The alloy exhibits a high resistance to crystallization on annealing below Tg and complex Pd- and Ni-phosphides evolve on annealing above Tg.

Biaxial strain induced electrical inhomogenities and phase separation in the ferromagnetic metallic phase in thin films of La0.7Ca0.3MnO3: A scanning tunneling potentiometry/spectroscopy study

We have investigated the effect of biaxial strain on local electrical/electronic properties in thin films of La0.7Ca0.3MnO3 with varying degrees of biaxial strain in them. The local electrical properties were investigated as a function of temperature by scanning tunneling spectroscopy (STS) and scanning tunneling potentiometry (STP), along with the bulk probe like conductance fluctuations.The results indicate a positive correlation between the lattice mismatch biaxial strain and the local electrical/electronic inhomogenities observed in the strained sample. This is plausible since the crystal structure of the manganites interfere rather strongly with the magnetic/electronic degrees of freedom. Thus even a small imbalance (biaxial strain) can induce significant changes in the electrical properties of the system.

Microstructure and mechanical properties of electron beam weld joints of a Zr41Ti14Cu12Ni10Be23 bulk metallic glass with Zr

The electron beam welding technique was used to join Zr41Ti14Cu12Ni10Be23 bulk metallic glass (BMG) to crystalline pure Zr. Compositional, microstructural, and mechanical property variations across the welded interface were evaluated. It is shown that a crystalline layer develops close to the welding interface. Transmission electron microscopy of this layer indicates the crystalline phase to be tetragonal with lattice parameters close to that reported for Zr2Ni. However, the composition of this phase is different as it contains other alloying additions. The interface layer close to the bulk metallic glass side contains nanocrystalline Zr2Cu phase embedded in the glassy matrix. Nanoindentation experiments indicate that the hardness of the crystalline layer, although less than the bulk metallic glass, is more than the Zr itself. Commensurately, tensile tests indicate that the failure of the welded samples occurs at the Zr side rather than at the weld joint.

Effect of Dilatation on the Elasto-Plastic Response of Bulk Metallic Glasses Under Indentation

Elasto-plastic response of bulk metallic glasses (BMGs) follows closely the response of granular materials through pressure dependent (or normal stress) yield locus and shear stress induced material dilatation. On a micro-structural level, material dilatation is responsible for stress softening and formation of localized shear band, however its influence on the macro-scale flow and deformation is largely unknown. In this work, we systematically analyze the effect of material dilatation on the gross indentation response of Zr-based BMG via finite element simulation. The strengthening/softening effect on the load-depth response and corresponding stress-strain profiles are presented in light of differences in elastic-plastic regimes under common indenters. Through comparison with existing experimental results, we draw conclusions regarding selection of suitable dilatation parameters for accurately predicting the gross response of BMGs

Formation of amorphous xenon nanoclusters and microstructure evolution in pulsed laser deposited Ti62.5Si37.5 thin films during Xe ion irradiation

As deposited amorphous and crystallized thin films of Ti 37.5% Si alloy deposited by pulsed laser ablation technique were irradiated with 100 keV Xe+ ion beam to an ion fluence of about 1016 ions-cm−2. Transmission electron microscopy revealed that the implanted Xe formed amorphous nanosized clusters in both cases. The Xe ion-irradiation favors nucleation of a fcc-Ti(Si) phase in amorphous films. However, in crystalline films, irradiation leads to dissolution of the Ti5Si3 intermetallic phase. In both cases, Xe irradiation leads to the evolution of similar microstructures. Our results point to the pivotal role of nucleation in the evolution of the microstructure under the condition of ion implantation.

A Study of Nanostructures of Thin Films in B–C–N System Produced by Pulsed Laser Deposition and Nitrogen Ion-Beam-Assisted Pulsed Laser Deposition

We report the synthesis of thin films of B–C–N and C–N deposited by N+ ion-beam-assisted pulsed laser deposition (IBPLD) technique on glass substrates at different temperatures. We compare these films with the thin films of boron carbide synthesized by pulsed laser deposition without the assistance of ion-beam. Electron diffraction experiments in the transmission electron microscope shows that the vapor quenched regions of all films deposited at room temperature are amorphous. In addition, shown for the first time is the evidence of laser melting and subsequent rapid solidification of B4C melt in the form of micrometer- and submicrometer-size round particulates on the respective films. It is possible to amorphize B4C melt droplets of submicrometer sizes. Solidification morphologies of micrometer-size droplets show dispersion of nanocrystallites of B4C in amorphous matrix within the droplets. We were unable to synthesize cubic carbon nitride using the current technique. However, the formation of nanocrystalline turbostratic carbo- and boron carbo-nitrides were possible by IBPLD on substrate at elevated temperature and not at room temperature. Turbostraticity relaxes the lattice spacings locally in the nanometric hexagonal graphite in C–N film deposited at 600 °C leading to large broadening of diffraction rings.

Reduction of oxygen impurity at GaN/beta-Si(3)N(4)/Si interface via SiO(2) to Ga(2)O conversion by exposing of Si surface under Ga flux

The removal of native oxide from Si (1 1 1) surfaces was investigated by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectra (SIMS) depth profiles. Two different oxide removal methods, performed under ultrahigh-vacuum (UHV) conditions, were carried out and compared. The first cleaning method is thermal desorption of oxide at 900 degrees C. The second method is the deposition of metallic gallium followed by redesorption. A significant decrease in oxygen was achieved by thermal desorption at 900 degrees C under UHV conditions. By applying a subsequent Ga deposition/redesorption, a further reduction in oxygen could be achieved. We examine the merits of an alternative oxide desorption method via conversion of the stable SiO(2) surface oxide into a volatile Ca(2)O oxide by a supply of Ga metals. Furthermore, ultra thin films of pure silicon nitride buffer layer were grown on a Si (1 1 1) surface by exposing the surface to radio-frequency (RF) nitrogen plasma followed by GaN growth. The SIMS depth profile shows that the oxygen impurity can be reduced at GaN/beta-Si(3)N(4)/Si interfaces by applying a subsequent Ga deposition/redesorption. (C) 2011 Elsevier B.V. All rights reserved.

High energy Li ion irradiation effects in ferroelectric PZT and SBT thin films

The ferroelectric Pb(Zr0.53Ti0.47)O-3 (PZT) and SrBi2Ta2O9 (SBT) thin films were prepared by laser ablation technique. The dielectric analysis, capacitance-voltage, ferroelectric hysteresis and DC leakage current measurements were performed before and after 50 MeV Li3+ ion irradiation. In both thin films, the irradiation produced some amount of amorphisation, considerable degradation in the ferroelectric properties and change in DC conductivity. On irradiation of these thin films, the phase transition temperature [T-c] of PZT decreased considerably from 628 to 508 K, while SBT exhibited a broad and diffuse transition with its T-c decreased from 573 to 548 K. The capacitance-voltage curve at 100 kHz showed a double butterfly loop with a large decrease in the capacitance and switching voltage. There was decrease in the ferroelectric hysteresis loop, remanant polarisation and coercive field. After annealing at a temperature of 673 K for 10 min while PZT partially regained the ferroelectric properties, while SBT did not. The DC conductivity measurements showed a shift in the onset of non-linear conduction region in irradiated SBT. The degradation of ferroelectric properties of the irradiated thin films is attributed to the irradiation-induced partial amorphization and the pinning of the ferroelectric domains by trapped charges. The regaining of properties after annealing is attributed to the thermal annealing of the defects generated during the irradiation. (C) 2003 Elsevier Science B.V. All rights reserved.

The Drude parameters for metallic PF6 doped polypyrrole

We measured the two components of the complex dielectric function of insulating and metallic PF6 doped polypyrrole up to 4 meV simultaneously. These data are used as an input performed Kramers-Kronig analysis on the higher energy reflection data. This has helped to clarify those results, which were previously deduced from the FIR and UV/VIS data, that could be artifacts.

Lamb wave based identification and parameter estimation of corrosion in metallic plate structure using a circular PWAS array

A circular array of Piezoelectric Wafer Active Sensor (PWAS) has been employed to detect surface damages like corrosion using lamb waves. The array consists of a number of small PWASs of 10 mm diameter and 1 mm thickness. The advantage of a circular array is its compact arrangement and large area of coverage for monitoring with small area of physical access. Growth of corrosion is monitored in a laboratory-scale set-up using the PWAS array and the nature of reflected and transmitted Lamb wave patterns due to corrosion is investigated. The wavelet time-frequency maps of the sensor signals are employed and a damage index is plotted against the damage parameters and varying frequency of the actuation signal (a windowed sine signal). The variation of wavelet coefficient for different growth of corrosion is studied. Wavelet coefficient as function of time gives an insight into the effect of corrosion in time-frequency scale. We present here a method to eliminate the time scale effect which helps in identifying easily the signature of damage in the measured signals. The proposed method becomes useful in determining the approximate location of the corrosion with respect to the location of three neighboring sensors in the circular array. A cumulative damage index is computed for varying damage sizes and the results appear promising.