Synthesis and thermoelectric power measurements of TlGaSe 2 single crystals
TlGaSe2single crystals were grown by modified Bridgman method. Thermoelectric power measurement were carried out in a brass working chamber designed for this purpose, allow measurements in a wide range of temperature under vacuum. The experimental results indicates that TlGaSe2 is of p-type conductivity. Throughout these measurements, various parameters such as effective mass of charge carriers, carrier mobility, diffusion coefficient, relaxation time and diffusion length for both majority and minority carriers were found. In addition to these pronounced parameters, the efficiency of the thermoelectric element (figure of merit) was evaluated, which leads to better application in many fields. [A. T. Nagat, S. A. Hussein, S. E. Al Garni. Synthesis and thermoelectric power measurements of TlGaSe2 single crystals. Life Sci J 2014;11(8):418-422]. (ISSN:1097-8135). http://www.lifesciencesite.com. 54
The optical investigation of TlGa0.999Pr0.001Se2 and TlGaSe2 single crystals
Abstract TlGaSe2 and TlGa0.999Pr0.001Se2 single crystals were grown by a method which is similar to the direct freezing method. They did not have cracks and voids on their surface. The freshly cleaved crystals had a mirror-like surface and there was no need for mechanical treatment. The absorption measurements were carried out on TlGaSe2 and TlGa0.999Pr0.001Se2 samples in the temperature range 10–320 K with a step of 10 K. The phonon energies calculated for TlGaSe2 and TlGa0.999Pr0.001Se2 are 34 and 26 meV, respectively. At 320 K, the direct band gaps of TlGaSe2 and TlGa0.999Pr0.001Se2 are 2.173 and 2.155 eV and the indirect band gaps are 2.054 and 2.044 eV, respectively. There are abrupt changes in the Urbach energy for TlGaSe2 at 180 and 210 K, and for TlGa0.999Pr0.001Se2 at 140 K. These temperatures obtained from the changing of Urbach energy may be phase transition temperatures.
Birefringence and the gyrotropy of the compounds II-IV-V2
ConclusionThe crystals II-IV-V2 with the structure of chalcopyrite exhibit intense birefringence whose quantity according to the structural model is determined by the anisotropy of the local field and by the anisotropy of the polarizability of the II–V bond. Birefringence dispersion and its thermal and barometric coefficients are interpreted in the three-contribution model as boundary, E1 and E2-transitions and correspond to a compressed binary analog. The crystals II-IV-V2 possess gyrotropic properties that are manifested in elliptical birefringence and exhibit peculiarities in the optical spectra near the isotropic point. The dispersion of gyrotropy is determined by the presence of linear terms in the dispersion zone. The quantity of gyrotropy is related to the deformation of the tetrahedron II-V4. The anisotropy of the optical properties of the crystals II-IV-V2 can be used for devices in nonlinear optics for the parametric transformation of light.