Electrical properties of crystalline synthetic zeolites types X and Y, exchanged with monovalent cations

Abstract

The electrical properties of anhydrous synthetic faujasites, exchanged with various monovalent cations have been measured between 250 and 730 K in the frequency range 200–10⁷ Hz. The zeolites had Si/Al ratios of 1.22, 1.75, 2.51 and 2.98. An ionic conduction phenomenon is predominant, especially above room temperature. The conductivity is determined by the mobility of the supercage cations. The migration from site II to the neighbouring site III′ is the rate-controlling step. The activation energies range between 50 and 90 kJ mol^–1. They are the sum of two terms: cation-lattice interaction and cation–cation repulsion. The latter is only appreciable in the samples with K⁺, Rb⁺ or Cs⁺ on sites III′. Below room temperature an intense dielectric relaxation is observed in samples with Si/Al ratios of 1.22 and 1.75. The activation energies for this process range between 30 and 43 kJ mol^–1. This relaxation is associated with the local motion of exchangeable cations over two neighbouring sites III′. It is very weak or nonexistent in samples with Si/Al ratios of 2.51 and 2.98, indicating that no, or nearly no, cations are located on sites III′.