Studies on grain boundary effects in spray deposited BICOVOX 0.1 films on platinum-coated stainless steel substrate

Abstract

Thin film of Bi 2 Co 0.1 V 0.9 O 5.35 is deposited by using spray pyrolysis technique on platinum-coated stainless steel substrate. Impedance measurements done in the frequency range 1 to 10 MHz and in the temperature range 502 to 720 K revealed two relaxation processes with distinguishable time constants. The first corresponds to the grain interior charge transfer while the second could be due to grain boundary. The change in polarization seems to be associated with hopping of charge carriers showing Arrhenius behavior with increase in temperature. The relaxation frequency of grain interior transport for the thin film ranges from 96 kHz to 2.59 MHz. The blocking factor was found to be increasing with increase in temperature at low temperature region from 502 to 640 K. At higher temperature above 640 K, diffusive nature of grain boundaries is inferred with the decrease in blocking factor. The same inference is derived by specific grain boundary conductivity calculations since specific grain boundary conductivity decreases in low temperature region while it increases rapidly at higher temperature. These observations prove the grain boundaries to be blocking in lower temperatures while at higher temperatures above 640 K they turn diffusive. These changes are attributed to structural phase transition, or ordering of vacancies in Bi 2 Co 0.1 V 0.9 O 5.35 films.

Anomalous current–voltage and impedance behaviour in doped Poly 3-methylthiophene devices

“…This is interesting because this tail in the Cole-Cole plot is observed in the same voltage region where I-V anomalies are observed. This kind of elongated tail is unusual and reported in few cases [40]. The length of this tail increases when the applied bias crosses a threshold value, which is the same as the threshold at which the NDR is be observed in I-V characteristics.…”