Temperature dependence of positron-annihilation lifetime, free volume, conductivity, ionic mobility, and number of charge carriers in a polymer electrolyte polyethylene oxide complexed with NH4ClO4

Abstract

Various physical properties of the solution-cast films of the proton conducting polymer polyethylene oxide (PEO) complexed with ammonium perchlorate (${\mathrm{NH}}_4$ ${\mathrm{ClO}}_4$) have been studied in the temperature range 300–370 K. These properties studied by us include free volume by positron lifetime spectroscopy, ionic conductivity by impedance spectroscopy, ionic mobility by transient ionic current technique, number of charge carriers, dielectric constant, etc. The hole volume and conductivity show a steep rise at T≃${\mathit{T}}_{\mathit{m}}$ (∼333 K). It appears that the increase in free volume arises out of the increase in the size of the holes rather than an increase in their number. Although the free volume shows an increase around ${\mathit{T}}_{\mathit{m}}$, the measured ionic mobility does not show similar behavior. The increase in the conductivity at ${\mathit{T}}_{\mathit{m}}$ is, therefore, ascribed to an increase in the number of charge carriers at ∼${\mathit{T}}_{\mathit{m}}$. A suitable dissociation model involving the dielectric constant is proposed to explain this increase. The value of the dissociation energy for PEO:${\mathrm{NH}}_4$ ${\mathrm{ClO}}_4$ has been determined to be 2.4 eV. © 1996 The American Physical Society.