Optical and thermal diffusivity measurement of Ge-Se-Te glasses by photoacoustic technique

The composition dependence of optical energy gap (E<SUB>g</SUB>) and thermal diffusivity a in three sets of Ge-Se-Te glasses, namely, Ge<SUB>x</SUB>Se<SUB>80-x</SUB>Te<SUB>20</SUB> (5 = x = 40), Ge<SUB>x</SUB>Se<SUB>75-x</SUB>Te<SUB>25</SUB> (5 ≤ x ≤ 40), and Ge<SUB>x</SUB>Se<SUB>65-x</SUB>Te<SUB>25</SUB> (5 ≤ x ≤ 37.5), have been studied using photoacoustic technique. The variation of a with average coordination number &lt;r&gt; shows a change in the slope at &lt;r&gt; = 2.4 and 2.67. E<SUB>g</SUB> shows a local maximum at &lt;r&gt; = 2.67. The results are discussed on the basis of the topological and chemical threshold exhibited by covalent network glasses. The relative sensitivity of a and E<SUB>g</SUB> to these phenomena is discussed