Enhancement in thermoelectric performance of SiGe nanoalloys dispersed with SiC nanoparticles

SiGe is one of the most widely used thermoelectric materials for radioisotope thermoelectric generator applications for harnessing waste-heat at high temperatures. In the present study, we report a simple experimental strategy for enhancing the thermoelectric and mechanical properties of n-type SiGe nanoalloys by dispersing SiC nanoparticles in a SiGe nanoalloy matrix. This strategy yielded a high value of figure-of-merit (ZT) of similar to 1.7 at 900 degrees C in the SiGe/SiC nanocomposite, which is nearly twice that reported for its pristine bulk counterpart and similar to 15% higher than that of pristine SiGe nanoalloys. This significant enhancement in the ZT primarily originates from a reduction in the lattice thermal conductivity, owing to a high density of nano-scale interfaces, lattice-scale modulations and mass fluctuations, which lead to extensive scattering of heat-carrying phonons. The dispersion of SiC nanoparticles also significantly enhances the mechanical properties of the resulting SiGe/SiC nanocomposite, including fracture toughness and hardness. The enhancement in the thermoelectric and mechanical properties of the SiGe/SiC nanocomposites has been correlated with their microstructural features, elucidated employing X-ray diffraction, and scanning and transmission electron microscopy

Mechanical properties and microstructure of spark plasma sintered nanostructured p-type SiGe thermoelectric alloys

SiGe based thermoelectric (TE) materials have been employed for the past four decades for power generation in radio-isotope thermoelectric generators (RTG). Recently "nanostructuring" has resulted in significantly increasing the figure-of-merit (ZT) of both n and p-type of SiGe and thus nanostructured Si80Ge20 alloys are evolving as a potential replacement for their conventional bulk counterparts in designing efficient RTGs. However, apart from Zr, their mechanical properties are equally important for the long term reliability of their TE modules. Thus, we report the mechanical properties of p-type nanostructured Si80Ge20 alloys, which were synthesized employing spark plasma sintering of mechanically alloyed nanopowders of its constituent elements with 12% boron doping. Nanostructured p-type Si80Ge20 alloys exhibited a hardness of similar to 9 +/- 0.1 GPa, an elastic modulus of similar to 135 +/- 1.9 GPa, a compressive strength of 108 +/- 02 MPa, and fracture toughness of similar to 1.66 +/- 0.04 MPalm with a thermal shock resistance value of 391 +/- 21 Wm(-1). This combination of good mechanical properties coupled with higher reported Zr of nanostructured p-type Si80Ge20 alloys are rendered to be a potential material for power generation applications, compared to its bulk counterpart

Up -converision fluorescence and low-temperature emission in Er-doped Ge-Ga-S-CsBr glasses

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Microstructure and mechanical properties of thermoelectric nanostructured n-type silicon-germanium alloys synthesized employing spark plasma sintering

Owing to their high thermoelectric (TE) figure-of-merit, nanostructured Si80Ge20 alloys are evolving as a potential replacement for their bulk counterparts in designing efficient radio-isotope TE generators. However, as the mechanical properties of these alloys are equally important in order to avoid in-service catastrophic failure of their TE modules, we report the strength, hardness, fracture toughness, and thermal shock resistance of nanostructured n-type Si80Ge20 alloys synthesized employing spark plasma sintering of mechanically alloyed nanopowders of its constituent elements. These mechanical properties show a significant enhancement, which has been correlated with the microstructural features at nano-scale, delineated by transmission electron microscopy

Multicolor and white light emitting Tb3+/Sm3+ co-doped zinc phosphate barium titanate glasses via energy transfer for optoelectronic device applications

A series of Tb3+/Sm3+ co-doped ZPBT glasses have been successfully prepared via melt quenching technique and their photoluminescence properties and energy transfer mechanism were investigated. Tb3+ doped glass exhibits dominant emission peak at 544 nm corresponding to D-5(4)-> F-7(5) transition under 375 nm excitation whereas Sm3+ doped glass exhibits intense emission peak at 599 nm corresponding to (4)G(5/2) -> H-6(7/2) under 399 nm excitation. The CIE chromaticity coordinates (0.259, 0.590) and (0.570, 0.428) are located in the pure green and orange region for Tb3+ and Sm3+ doped glasses, respectively. The Tb3+/Sm3+ co-doped glasses under 375 nm excitation emit a combination of blue, green and orange-red light while under 484 nm excitation emits green and red-orange emission light. The energy transfer occurs from Tb3+ to Sm3+ via dipole-dipole interaction, which was confirmed by applying Dexter and Reisfeld's theory and Inokuti Hirayama (I-H) model. Moreover, the energy transfer efficiencies and probabilities were calculated from the decay curves. The color tone of these glasses can be modulated from yellowish-green to warm-white via greenish-yellow by appropriate tuning of Sm3+ concentrations and excitation wavelengths. These results indicate that the prepared glasses can be a potential candidate for white light as well as solid state lighting applications

Up-conversion fluorescence and low-temperature emission in Er3+-doped GeGaS-CsBr glasses

Optical properties of Er-doped chalcohalide GeGaS-CsBr glasses have been investigated as a function of Er and Ga concentrations. Nominal compositions of (Ge0.25Ga.S-0.10(0.65))(0.9)(CsBr)(0.1) and (Ge0.23Ga.S-0.12(0.65))(0.9) (CsBr)(0.1) glassy hosts have been chosen for this study. The effects of Er content and host composition on 1.5 mu m emission of Er3+ ions, measured at low-temperature of 20 K under excitation by 514.5 nm, have been specified. Besides, the up-conversion fluorescence of Er3+ ions pumped at 795 nm is reported. Two intense emission bands in the green and one weak emission band in the red regions around 530, 554 and 644 nm have been observed, and were attributed to H-2(11/2)-> I-4(15/2), S-4(3/2)-> I-4(15/2), and F-4(9/2)-> I-4(15/2) transitions of Er3+ ions, respectively. The simplified energy-level diagram of Er3+ ion has been used to identify the observed up-conversion fluorescence bands in visible region. (C) 2010 Elsevier B.V. All rights reserved.X1145sciescopu

Tb3+ and Eu3+ Doped Zinc Phosphate Glasses for Solid State Lighting Applications

Tb3+ and Eu3+ doped zinc phosphate (ZP) glasses were prepared by conventional melt-quenching technique and their photoluminescence properties were investigated in detail. For, Tb3+ doped glasses the intense emission was at 545 nm corresponding to D-5(4)-> F-7(5) transition under 377 nm n-UV excitation. The optimized concentration for Tb3+ doped zinc phosphate glass was 3 mol% and above this concentration quenching takes place. The Eu3+ doped zinc phosphate glass revealed intense emission at 613 nm attributed to the D-5(0)-> F-7(2) transition under intense 392 nm n-UV excitation. The concentration quenching phenomenon was not observed in the Eu3+ doped ZP glasses. The CIE chromaticity coordinates for 3 mol% Tb3+ and 5 mol% Eu3+ doped ZP glasses were found to (0.283, 0.615) and (0.652, 0.331) lying in the green and red regions, respectively. The above mentioned results indicate that the prepared glass are suitable for application in the field of lighting and display devices

THE INFLUENCE OF CSBR ADDITION ON OPTICAL AND THERMAL PROPERTIES OF GEGAS GLASSES DOPED WITH ERBIUM

The influence of the addition of CsBr on the optical and thermal properties of GeGaS glass doped with Er has been being investigated. We find that the addition of CsBr into GeGaS glass leads to some improvements in the radiative properties of Er3+ ions in this glass system. The GeGaS-CsBr glasses demonstrate much longer radiative lifetimes and stronger photoluminescence for I-4(13/2) -> I-4(15/2) and H-2(11/2) -> I-4(15/2) transitions in Er3+ ions. Very low Judd-Ofelt parameters and sharp Er3+ absorption spectra with multiple peaks suggest the presence of microcrystals. All optical parameters are strongly influenced by the interplay of Ga and CsBr. The glasses studied have been characterized by their basic glass transformation temperatures. The addition of CsBr into GeGaS glass keeping the ratio between CsBr and Ga close to unity is favorable for the incorporation of larger amount of Er. The experimental results are discussed in terms of structural local arrangement induced by CsBr addition.X111sciescopu