Showing papers on "Variable-range hopping published in 1973"

Small polaron conduction in V2O5P2O5 glasses

Abstract: Dc conductivity measurements have been made between 90 and 520 K on three bulk samples of V 2 O 5 P 2 O 5 glass. Heat treatment is found to result in a reduction of the activation energy at a given temperature and this is most noticeable at low temperatures. The behaviour at low temperatures can be described using Mott's variable range hopping arguments, and at high temperatures by non-adiabatic small polaron hopping between nearest neighbours. At intermediate temperatures a simple model is used in which excitations by optical and acoustic phonons are considered to make independent contributions to the jump frequency. Mott's theory is extended to the polaron case for T> 1 4 ⊖ and is shown to be in good agreement with results. Values for r p (∼2.8 A ) the polaron radius and α(∼3.5 A −1 ) the electron decay constant are shown to be consistent with the model for small polarons. A method is suggested for obtaining α and N ( E F ) from the ac conductivity and the slope of 1nσ versus 1 T 1 4 at low temperatures. Values of N ( E ) are obtained which correlate with those obtained by the previous analysis. This implies that the disorder energy separating adjacent sites Δ 0 is large (∼0.4 eV) in these materials.