Temperature dependence of the fundamental absorption edge in Cu2GeSe3

The temperature dependence of the energy gap E-G in Cu2GeSe3 has been obtai ned from optical absorption measurements in the temperature range from 10 t o 300 K. X-ray powder diffraction analysis indicates that the compound crys tallizes in an orthorhombic structure with the unit cell parameters a = 11. 878(8), b = 3.941(3), and c = 5.485(3) Angstrom. The data were analyzed by considering several models reported in the literature for the variation of E-G vs T. The best fit was obtained by using an expression proposed by Pass ler [Phys. Status Solidi B 200, 155 (1997)]. From the analysis, the Debye t emperature was estimated to be around 170 K. Also obtained was the fact tha t the effective energy of phonons that participate in the shift of the band gap with temperature is about 15 meV and corresponds to the acoustic phono n branch. (C) 2000 American Institute of Physics. [S0021-8979(00)09901-1].