Larissa Duran

Ingots of the Ag(In1-xGax)5Te8 (0≤x≤1) system were prepared by direct fusion of the stoichiometric mixture of the elements in evacuated quartz ampoules. The analysis of the X-ray powder diffraction data showed the presence of a single phase with tetragonal structure at room temperature for all the studied compositions. The lattice parameters a and c were calculated. Melting temperatures, from 696 ºC for AgIn5Te8 to 775 ºC for AgGa5Te8, were obtained from Differential Thermal Analysis measurements performed on samples in evacuated quartz ampoules. Reflectance measurements were used to calculate the band gap energies and the real refraction indices. A direct band gap, slightly varying from 1.34 to 1.39 eV (0≤x≤0.4), was found in In-rich compounds, while an indirect band gap was found in all the studied compositions varying from 1.11 to 1.14 eV (0≤x≤1).

... The va lue of the energy gap Eg for each com po si tion was ob tai ned from fi tting the nu me ri ca lly ob tai ned se cond de ri va ti ve spec tra of the ex pe ri men tal data e(hn), d2e(hn)/d(hn)2, to analytic cri ti cal-point line sha pes. ...

A polycrystalline ingot of In0.8Mn0.2Sb was synthesized by direct fusion and subsequent controlled cooling of the stoichiometric mixture of the constituent elements in a pyrolysis-graphited and evacuated quartz ampoule. The analysis of the X-Ray powder diffraction pattern showed the presence of a cubic phase at room temperature and the existence of minority secondary phases. The program Fullprof was used to index the diffraction pattern and to calculate the lattice parameter, giving a = 6.439631 A and cell volume V = 267.04 A3. The phase transition temperatures were obtained from Differential Thermal Analysis (DTA) measurements performed on powder samples in evacuated quartz ampoules. The studied compound melts incongruently between 479 oC and 519 oC.