E.Kh. Shokr

Structural and kinetic evaluation of Sn?Sb?Se alloys

SnxSb20Se80−x chalcogenide alloys (with x = 8, 10, 12, 13.5, 15, 16.5 and 18 at.%) were prepared by the melt quenching technique. The average coordination number and the overall mean bonding energy were calculated. The x-ray diffraction studies revealed that the alloys with x = 8 and 10 at.% were amorphous and the alloy with x = 12 at.% was partially crystalline whereas the alloys with x = 13.5, 15, 16.5 and 18 at.% were crystalline. The glass transition temperature, the crystallization temperature, the melting temperature and the glass-forming tendency of the amorphous samples were determined from the differential scanning calorimetry measurements. The glass transition activation energies and the crystallization activation energies were determined using Kissinger as well as Augis and Bennett methods. Upon annealing the bulk amorphous samples at 573 K, two different crystalline phases, SnSe2 and Sb2Se3, were observed. X-ray reflectometry analysis revealed that the surface roughness increased with increasing annealing temperature. The density of the as-prepared films increased with increasing Sn content. Upon annealing at 523 K the density increased, whereas the density of most of the films decreased upon annealing at 573 K. Thermal gravimetric analysis showed a steeper weight loss upon heating after 533 K.

Optical parameters of as-deposited and annealed GeSe0.5Te3.5 films

Abstract Some optical parameters of as-deposited and annealed GeSe 0.5 Te 3.5 thin films were studied in the visible spectral range using both absorbance and transmittance measurements. The heat treatment of the films proved that the variations of these optical parameters can be interpreted as a consequence of the internal microstructural changes caused by annealing. The increase of the optical gap with both annealing and increasing Se-Te ratio was explained in terms of diminution of disorder and defects in the structural bonding.

Structural, electrical, and thermoelectrical properties of (Bi1 − xSbx)2Se3 alloys prepared by a conventional melting technique

Polycrystalline solid solutions of (Bi1 − xSbx)2Se3 (x = 0, 0.025, 0.050, 0.075, 0.100) were prepared using a facile method based on the conventional melting technique followed by annealing process. X-ray analysis and Raman spectroscopical measurements revealed formation of Bi2Se3 in single phase. The electrical and thermoelectric properties have been studied on the bulk samples in the temperature range 100–420 K. The electrical conductivity measurements show that the activation energy and room-temperature electrical conductivity dependences on the Sb content respectively exhibit minimum and maximum values at x = 0.05. The thermoelectric power exhibited a maximum value near the room temperature suggesting promising materials for room-temperature applications. The highest power factor value was found to be 13.53 μW K−2 cm−1 and recorded for the x = 0.05 compound.

Effect of heat treatment on the electrical and thermoelectric properties of Sb doped Bi2Se3

Polycrystalline samples of (Bi0.95Sb0.05)2Se3 were prepared using the conventional melting technique at 1273 K, followed by annealing at different temperatures (423, 473, 523 and 573 K) for different time intervals (4, 8, 12 and 16 h). The samples were crystallized in a single phase of Bi2Se3 and no other phases or impurities were observed. The electrical and thermoelectric properties were studied by measuring the electrical conductivity and Seebeck coefficient as functions of temperature in the range 100–400 K. The results exhibited a metal–n-type semiconductor transition for all samples. The power factor (Pf) was calculated to determine the effect of the annealing treatment on the performance of the prepared material as a thermoelectric power generator. The highest room temperature value of the Pf was 6.9 μWK−2cm−1 and was recorded for the sample annealed at 573 K for 16 h. The results confirm the feasibility of using the annealing process to improve the performance of thermoelectric materials.