Electric Dipoles and Ionic Conductivity in a Na+ Glass Electrolyte

Authors: M. Helena Braga, Jorge A. Ferreira, Andrew J. Murchison and John B. Goodenough

Glass, unlike a crystalline solid, contains atoms and molecules that do not occupy fixed positions. A glass that contains molecules that attract one another can age with time. We report such a glass that contains A₂O and (OA)⁻ electric dipoles (A = Li or Na). At a temperature T < 1.2T_g ≈ 110°C (T_g is the glass transition temperature) the electric dipoles coalesce with time into clusters within which, unlike in ice, some dipoles condense into ferroelectric, negatively charged molecules locally charge-compensated by weakly attracted A⁺ ions. In an applied electric field, the dipoles are oriented and, over time depending on the T < 110°C, are aligned parallel to the field axis to yield a solid A⁺ electrolyte with an ionic conductivity σ_i > 10⁻² S cm⁻¹ and a huge dielectric constant that makes it suitable for many applications, including safe rechargeable batteries of high energy density and long cycle life.