Thermoelectric Properties of Fe0.2Co3.8Sb12-xTex ... - Physics

A Unique Electrical switching behavior in Cu-As-Se glasses
K. Ramesh
Department of Physics, Indian Institute of Science, Bangalore 560012, India.
ABSTRACT
A unique electrical switching behaviour has been observed in Cu x As 40 Se 60-x glasses over
a wide range of composition (0 ≤ x ≤ 32). The glasses with lower Cu concentrations (x < 15) do
not exhibit switching, whereas glasses in the range 15 ≤ x ≤ 25 show a threshold type switching.
The glasses in the range 25 ≤ x ≤ 28 exhibited an unusual switching from low resistance to high
resistance state. For x ≥ 30, the glasses are found to show a memory switching. This is a unique
observation and for the first time a system showing no switching → threshold switching → low
resistance to high resistance switching
→
memory switching has been observed.
The thermal crystallization of Cu x As 40 Se 60-x glasses at their respective crystallization
temperatures indicate that the structural network is mainly characterized by Cu 3 AsSe 4 and
As 2 Se 3 for x < 15 and by Cu 3 AsSe 4 and Cu 2 As 3 for x ≥ 25. The composition range 15 ≤ x ≤ 20 is
characterized only by Cu 3 AsSe 4 structural units. The samples cooled from their melt show only
the ternary Cu 3 AsSe 4 for x ≤ 20. For x > 20, precipitates of ‘As’ has also been observed along
with Cu 3 AsSe 4 and Cu 2 As 3 phases.
Normally, the memory switching is explained with the thermal model and threshold
switching is explained with the electronic model. The present studies provide a unique way to
understand the electrical switching exhibited by chalcogenide glasses based on the thermal mode
and filament formation. The proposal of the influence of cross-linking and rigidity of the
structural network in changing the switching type from memory to threshold and vice versa is
also ruled out by the present studies.