Broadband Colossal Dielectric Constant in the Superionic Halide RbAg4I5: Role of Intercluster Ag+ Diffusion

Abstract

Materials with ultrahigh dielectric constants and a low value of dielectric loss are important for energy storage and electronic devices. Traditionally, high dielectric constant is found in ferroelectric complex oxides, but they exhibit high dielectric loss as well. Herein, a broadband colossal dielectric constant in a superionic halide, RbAg4I5, with a low dielectric loss is presented. The real part of the dielectric constant, ε′, increases by 102 orders of magnitude as RbAg4I5 goes through a superionic transition at 121 K. At room temperature, ε′ > 106 in the frequency range 10–1 to 104 Hz with a low dielectric loss, which ranges between 2.03 and 0.53. The maximum of ε′ reaches a colossal value of 6.4 × 108 at 0.1 Hz at 300 K. The molecular dynamics simulation reveals the presence of Ag+ clusters with a broad size distribution. The intercluster diffusion of Ag+ causes significant instantaneous charge separation and a consequent large fluctuation in the dipole moments. The fluctuating dipoles, in turn, result in the colossal dielectric constant in RbAg4I5.