The phase diagram of the Cu(In1−xGax)5Se8 (0 ≤ x ≤ 1) alloy system, prepared by direct fusion of the stoichiometric mixture of the elements, has been established by X‐ray diffraction (XRD) and differential thermal analysis (DTA). The presence of a tetragonal structure at room temperature is found in the composition range 0.4 ≤ x ≤ 1.0. The reason for the reported tetragonal and hexagonal structures of CuIn5Se8 an also their co‐existence below x < 0.4 observed in the present work is explained. In the composition range 0 ≤ x ≤ 1, the unit cell lattice parameters a and c of the tetragonal phase vary from 5.73–5.48 Å and 10.90–11.56 Å, respectively. From the absorption coefficient spectra, the band gap energy is found to vary from about 1.17 to 1.85 eV, with a downward bowing parameter b2 ≈ 0.21 eV. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ag In 5 Te 8 was prepared by direct fusion of the stoichiometric mixture of the elements in an evacuated quartz ampoule. The analysis of x-ray powder diffraction data showed the presence of one single phase with tetragonal structure. The lattice parameters a=6.212Å and c=12.456Å were refined by means of the program WINPLOTR. Congruent fusion at 698°C was observed by differential thermal analysis measurements performed on samples sealed in evacuated quartz ampoules. Transmittance measurements were used to determine the absorption coefficient α. Two absorption edges were observed, one indirect at 1.1eV and one direct at 1.28eV, obtained from a plot of (α×hν)1∕2 vs hν and (α×hν)2 vs hν, respectively. A six-probe configuration was used to measure the electrical resistivity and the Hall coefficient from 10to400K. The activation energies values, estimated at 1.1 and 1.27eV from Arrhenius plots of the resistivity and the Hall coefficient, respectively, agree with those obtained for the energy gaps by optical measurements.
Compounds of the chalcogenide family Ag–In–VI (VI = S, Se, Te) are interesting materials due to their stoichiometric stability and potential application in nonlinear optics and solar cells. A polycrystalline ingot of AgIn5S8, an ordered vacancy semiconductor, was prepared by direct fusion of the stoichiometric mixture of the elements in an evacuated quartz ampoule. The presence of a single phase with cubic structure was confirmed by X-ray powder diffraction at room temperature. The lattice parameter, [Formula: see text], was calculated, giving 10.821750 Å. Samples in evacuated quartz ampoules were used to perform Differential Thermal Analysis measurements, showing congruent melting at 1110[Formula: see text]C. Transmittance and reflectivity measurements were used to calculate the absorption coefficient [Formula: see text]. From the plot of ([Formula: see text])2 versus [Formula: see text], two direct transitions are observed at 1.25 eV and 1.88 eV. While the higher energy direct transition has been observed by other authors, the direct nature of the lower energy transition was confirmed from the fitting of the plot of the reflectivity versus 1/[Formula: see text] between 0.53 eV[Formula: see text] (1.89 eV) and 0.55 eV[Formula: see text] (1.82 eV), obtaining a value of 1.29 eV. The real refractive index [Formula: see text] and the high-frequency dielectric constant [Formula: see text] were also obtained from the fit of the reflectivity, resulting to be 2.68 and 7.2, respectively.
Ingots of the CuAl x Ga 1-x Se 2 (0 ≤ x ≤ 1) alloys system were prepared by direct fusion of the stoichiometric mixture of the elements. The analysis of X-ray Powder Diffraction data showed the presence of one single phase with chalcopyrite tetragonal structure at room temperature for all the studied compositions. The lattice parameters, a and c, and the bond lengths were calculated. The phase transition temperatures were obtained by the onset method from Differential Thermal Analysis measurements performed on samples sealed in evacuated quartz ampoules. Fusion or transition enthalpies were determined from the area of the corresponding DTA peak.
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