Abstract
The random free energy barrier hopping model is proposed to explain the ac conductivity (σac) of chalcogenide glasses. The Coulomb correlation is consistently accounted for in the polarizability and defect distribution functions and the relaxation time is augmented to include the overlapping of hopping particle wave functions. It is observed that ac and dc conduction in chalcogenides are due to same mechanism and Meyer-Neldel (MN) rule is the consequence of temperature dependence of hopping barriers. The exponential parameter s is calculated and it is found that s is subjected to sample preparation and measurement conditions and its value can be less than or greater than one. The calculated results for a − Se, As2S3, As2Se3 and As2Te3 are found in close agreement with the experimental data. The bipolaron and single polaron hopping contributions dominates at lower and higher temperatures respectively and in addition to high energy optical phonons, low energy optical and high energy acoustic phonons also contribute to the hopping process. The variations of hopping distance with temperature is also studied. The estimated defect number density and static barrier heights are compared with other existing calculations.
Highlights
Observation of the low frequency ac conductivity σ(ω) at low temperature being proportional to the applied field frequency ω to the power 1 − s′ i.e σ(ω) = Aωs where A is complex constant and s and s′ are less than one.[1,2] This is obiquitous feature of hopping conduction.[3]
It is assumed that electron wave functions are well localized within the potential wells of specific defect sites D+ and D− and ac conduction is due to bipolaron hopping between these defect sites.[8,9,10]
This proposed correlated barrier hopping (CBH) model is used to explain the salient features of temperature dependence of ac conductivity of chalcogenide glasses
Summary
The CBH model is extended by including single polaron hopping and the results for undopped and doped chalcogenides are explained. Takano et al.[15] added the contribution of simple pairs in the CBH model to explain the pronounced peaks in the temperature dependent ac conductivity of transition metal atom doped As2Se3. Prakash et al.[29] used extended pair model and random free energy barriers to obtain the Meyer -Neldel formula for dc conduction in chalcogenide glasses. It is found that Meyer -Neldel energy originates from temperature induced configurational and electronic disorders and it depends upon intersite separation and radius of localized states We found it interesting to extend random free energy barrier hopping [RFBH] model to calculate ac conductivity of chalcogenide glasses.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
