Unusual Fast Cation Conduction in the High-Temperature Phase of Lithium Sodium Sulfate

Abstract

ABSTRACTLithium sodium sulfate (LiNaSO4) belongs to a group of simple inorganic salts exhibiting fast-cation conducting high-temperature phases with rotationally disordered anions. The analysis of a combination of quasielastic neutron scattering and high-frequency (10 MHz to 60 GHz) conductivity measurements in the high-temperature phase of LiNaSO4 reveals an unusual cation conduction mechanism: the Haven ratio, HR = D*/Dσ, turns out to be considerably larger than one. This behavior, to our knowledge detected for the first time in a typical fast ion conductor, can be traced back to a charge correlation factor clearly smaller than unity, indicating that charge transport is less effective than tracer transport in this material.