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In this study, presents the results of structural properties obtained by SEM, DRX and Mössbauer spectrocopy of the alloys systems Fe0.4Mn0.2Al0.4 obtained by mechanically alloying, with 2, 4, 6, 8, 12, 24 y 48 h alloying time. It was observed that, both the progressive consumption of crystalline Fe, Mn and Al parent powders and the progressive disappearance of the ferromagnetic behavior of the Fe grains take place to the occurrence of the solid state reaction, leading to the formation a FeMnAl ternary alloy, the alloys with 48 h consolidated in a bcc phase, with a mean grain size of ≈ 168 ± 3 A and with a lattice parameter in according with that waited for this phase. The sheets to consist of this time, have size the particle nearly constant of ≈ 110µm. The alloy consolited show a paramagnetic phase. In the process of formation, three regimes can be distinguished from the evolution of both room temperature Mössbauer spectra and X-ray pattern as a function of alloying time. [ABSTRACT FROM AUTHOR]

In this study, presents the results of structural properties obtained by SEM, DRX and Mössbauer spectrocopy of the alloys systems Fe0.4Mn0.2Al0.4 obtained by mechanically alloying, with 2, 4, 6, 8, 12, 24 y 48 h alloying time. It was observed that, both the progressive consumption of crystalline Fe, Mn and Al parent powders and the progressive disappearance of the ferromagnetic behavior of the Fe grains take place to the occurrence of the solid state reaction, leading to the formation a FeMnAl ternary alloy, the alloys with 48 h consolidated in a bcc phase, with a mean grain size of ≈ 168 ± 3 Å and with a lattice parameter in according with that waited for this phase. The sheets to consist of this time, have size the particle nearly constant of ≈ 110µm. The alloy consolited show a paramagnetic phase. In the process of formation, three regimes can be distinguished from the evolution of both room temperature Mössbauer spectra and X-ray pattern as a function of alloying time [ABSTRACT FROM AUTHOR]

We present results of a thermal anneal process that increases the minority carrier lifetime in SiC substrates to in excess of 3 μs, compared to the starting as-grown substrates with lifetimes typically in the <10 ns range. Measurement of lifetimes was conducted using microwave-photoconductive decay. Electron beam induced current measurements exhibited minority carrier diffusion lengths of up to 65 μm, confirming the enhanced carrier lifetime of the annealed substrate material. Additionally, positron annihilation spectroscopy and deep level transient spectroscopic (DLTS) analysis of samples subjected to this anneal process indicated that a significant reduction of deep level defects, particularly Z1/Z2, may account for the significantly enhanced lifetimes. The enhanced lifetime is coincident with a transformation of the original as-grown crystal into a strained or disordered lattice configuration as a result of the high temperature anneal process. The operational performance of p-i-n diodes employing drift layers fabricated from the annealed high-lifetime substrates confirmed conductivity modulation in the diodes consistent with ambipolar carrier lifetimes in the microsecond range. [ABSTRACT FROM AUTHOR]

This report presents an assessment of the efficiency and power density limitations of thermophotovoltaic (TPV) energy conversion systems for both ideal (radiative limited) and practical (defect-limited) systems. Thermodynamics is integrated into the unique physics of TPV conversion, and used to define the intrinsic tradeoff between power density and efficiency. The results of the analysis reveal that the selection of diode band gap sets a limit on achievable efficiency well below the traditional Carnot level. In addition it is shown that filter performance dominates diode performance in any practical TPV system and determines the optimum band gap for a given radiator temperature. It is demonstrated that for a given radiator temperature, lower band-gap diodes enable both higher efficiency and power density when spectral control limitations are included. The goal of this work is to provide a better understanding of the basic system limitations that will enable successful long-term development of TPV energy conversion technology. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Evaluates the electrical characterization of plasma-grown gallium arsenide oxides on gallium arsenide. Details on the experiment; Properties of gallium arsenide oxides; Information on the damage effects.

Amorphous samples of nominal composition Co62Nb6Zr2B30 have been prepared using mechanical alloying (MA) and rapid quenching (RQ) techniques. Differences appear in Curie temperature and the phases developed after crystallization. Refrigerant capacity is enhanced 20% in the MA-sample with respect to that of RQ-sample. Neglecting the demagnetizing factor of powder samples significantly affects the exponent n characterizing the field dependence of the maximum magnetic entropy change. [ABSTRACT FROM AUTHOR]

The influence of different compositional modifications on the magnetic entropy change and refrigerant capacity of Finemet, Nanoperm, HiTperm, and bulk amorphous alloys is presented. For all the studied alloys, the field dependence of the magnetic entropy change exhibits a quadratic dependence in the paramagnetic regime, a linear dependence in the ferromagnetic temperature range, and a potential law with a field exponent ∼0.75 at the Curie temperature. This exponent can be explained using the critical exponents of the Curie transition. It is shown that for alloys of similar compositional series, the magnetic entropy change follows a master curve behavior. [ABSTRACT FROM AUTHOR]