PREPARATION, CRYSTAL STRUCTURE, THERMAL ANALYSIS, SCANNING ELECTRON MICROSCOPY AND OPTICAL BAND-GAPS OF Cu2GeTe4 AND Cu2SnTe4 ALLOYS

Abstract

Polycrystalline samples (weight ~ 1g) of Cu2GeTe4 and Cu2SnTe4 alloys were prepared by the usual melt and anneal method and the products characterized by X-Ray Diffraction (XRD), Differential Thermal Analysis (DTA), Scanning Electron Microscopy (SEM) and Optical Diffuse Reflectance UV/VIS/NIR Spectroscopytechniques. It was found that: a) Cu2GeTe4 and Cu2SnTe4 crystallize in an orthorhombic structure (s.g. Imm2; No 44) with lattice parameters a=5.9281(4) Ã…, b=4.2211(6) Ã…, c=12.645(5) Ã… and a=6.0375(6) Ã…, b= 4.2706 (3) Ã…, c=12.844(1) Ã…, respectively; b) both alloys show two thermal transitions: 762 and 636K upon heating and; 700 and 578K upon cooling for Cu2GeTe4; 702 and 636K upon heating and; 650 and 590K upon cooling for Cu2SnTe4; c) both alloys present large deviations of stoichiometry for the cations Cu (~35%), Ge (7.2%) and Sn (26.4%) and minor deviation within the experimental error, for the anion Te; and, d) the measured optical band gaps were 0.63 and 0.53 eV for Cu2SnTe4 and Cu2GeTe4, respectively.