Electrical conductivity and dielectric properties of bulk glass Se55Ge30As15 chalcogenide

Measurements of conductivity (AC and DC), dielectric constant epsilon'(omega) and dielectric loss epsilon"(omega) have been made for bulk glassy samples of Se55Ge30As15 alloy in the frequency range from 10kHz to 10MHz and within the temperature range from 350 to 500K. The DC conductivity shows an activated behavior above 370 K, giving a conduction activation energy Delta E = 0.83 eV. The AC conductivity sigma(ac) (omega) was found to be temperature independent and vary as omega(s) with s = 0.994, where s is the frequency exponent. The charge-transfer process explained via CBH model with centers of intimate valence alternation pairs (IVAPs) type, giving a maximum barrier height W-M = 2.23 eV and density of localized states N (E-F) = 1.67 x 10(20) cm(-3). The dielectric constants behavior, reveal that the tested bulk Se55Ge30As15 chalcogetride exists in the form of molecular dipoles which remain frozen at low temperatures and, as the temperature is increased, the molecules attain freedom of rotation at temperatures above 370 K. The experimental results also gave a direct evidence of the existence of a Debye-type relaxation having a wide distribution of relaxation times. The most probable value of a spread of relaxation times have been estimated as tau = 4.13 x 10(-6) s. (c) 2006 Elsevier B.V. All rights reserved.