Sivaraman Guruswamy

Influence of ordering on the magnetostriction of Fe–27.5 at. % Ga alloys

Fe–Ga alloys with compositions near 27.5 at. % Ga (26–29 at. %) can be heat treated to obtain ordered phases based on α″ (ordered bcc), D019 (ordered hexagonal), and L12 (ordered fcc) structures. This work presents an evaluation of how the different ordering treatments influence the magnetostriction in cast polycrystalline Fe–27.5 at. % Ga alloy. Alloy samples were annealed first in the disordered bcc (A2) phase region to obtain a disordered bcc solid solution, followed by ordering-heat treatment in the appropriate temperature region of stability of each of the ordered phases. X-ray diffraction was used to characterize the phases present prior to and after heat treatments. Magnetostriction measurements were carried out at different prestress levels in the range of 0–50 MPa. Magnetic properties were measured using a vibrating sample magnetometer. Annealed Fe–27.5 at. % Ga sample with a disordered bcc (A2) structure and a weak [110] texture showed a magnetostriction value of 115×10−6. The α″ ordering treatm...

Importance of barrier layers in thermal diodes for energy conversion

Very high thermal to electric conversion efficiencies have been reported previously with thermal diode structures in which a thin n-type emitter layer is formed on the hot side of a thick near-intrinsic thermoelectric semiconductor. The figure of merit derived from direct measurements of electrical parameters and heat flow is increased by as much as a factor of eight. The question of what physical mechanisms are involved has been of interest since the initial observations of the effect. We have conjectured that the short-circuit current injection in these experiments is due to a second-order thermionic injection mechanism. More recently, we proposed that the open-circuit voltage comes about due to the presence of a p-type blocking layer between the emitter and the near-intrinsic bulk region. The experiments reported here show that a p-type blocking layer is required for the effect, and the dependence of conversion efficiency on the blocking layer concentration and width is studied. The results are general...

Ordering, magnetostriction, and elastic properties in Fe-27.5 at. % Ga alloy single crystals

Fe–Ga alloys, with composition around 27.5at.% Ga, can be heat treated to obtain α (A2, bcc), α″ (D03-like, ordered bcc), β-Fe3Ga (D019, ordered hexagonal), and α-Fe3Ga (L12 ordered fcc) phases. In this work, the influence of α″ ordering on the magnetostriction coefficient (3∕2) λ100, elastic constants (C11, C12, and C44), and the magnetomechanical coefficients (B1) of the single crystals of α-Fe-27.5at.% Ga and α″-Fe-27.5at.% Ga alloy is examined. Single crystals of Fe-27.5at.% Ga were grown using the vertical Bridgman technique. Magnetostriction measurements were performed using [100]-oriented single crystals. Elastic constants were estimated using resonant ultrasound spectroscopy and analysis technique. It is shown that the α″ ordering in Fe-27.5at.% Ga alloy decreases the (3∕2) λ100 value from that of α phase. This is consistent with our previous work on polycrystalline Fe-27.5at.% Ga alloys. The α-Fe-27.5at.% Ga alloy single crystal was found to have a higher magnetoelastic coupling constant than the...

Effect of Magnetic Field on the Corrosion Behavior of Magnetostrictive Iron-Gallium Alloy Single Crystals

Abstract This paper reports the first study on the effect of magnetic field application on the corrosion behavior of single crystals of magnetostrictive Fe-Ga alloys. The effect of a magnetic field...

Update on thermal diodes

Experiments on thermal diodes in InSb constructed with a p-type blocking layer in an n*pn structure have shown the existence of an optimum in acceptor concentration and width. Results for various potential barrier shapes show that triangle-shaped barriers outperform barriers with rectangular shape. Enhancements have been demonstrated in PbTe thermal diodes. In InSb and in PbTe diodes, the optimum width is on the order of the scattering length, which is different in the two semiconductors by an order of magnitude.

Heat To Electricity Conversion With Thermal Diodes

Thermal diodes are semiconductor devices with n*/p/n basic configuration. They show efficiencies that are multiples of substrate thermoelectric materials. MCT/InSb combinations demonstrated efficiencies in excess of 40% of ideal Carnot cycle. Current paper addresses switching to less exotic materials with enhanced thermal stability. Thermal diode principle of operation, multiple barrier approach, experimental and modeling data are presented.