Structural Phase Transitions and Solid State Chemical Reactions in Complex Potassium Hydrogen Sulfate Salts Driven by Fast Proton Diffusion

Abstract

At elevated temperatures the crystals of complex acid salts K m H n (SO 4 )(m + n)/2 . xH 2 O (0 ≤ x ≤ 1, m > 3, n ≥ 1) exhibit an anomalous temperature behavior of the dielectric permittivity and conductivity similar to the behavior observed in pure KHSO 4 at the structural phase transition or on melting. This unusual behavior is due to the formation of multiphase states at higher temperatures where phases with different chemical composition coexist. It is shown that K 3 H(SO 4 ) 2 undergoes a ferroelastic phase transition between the point groups 3 2/m with anomalously slow kinetics at 463 K while the multiphase state is formed near 480 K