CATION-TRANSPORT MECHANISMS IN HIGH-TEMPERATURE ROTOR PHASES OF SULFATES

Several high-temperature sulfate phases are plastic crystals, i.e., rotor phases. Their electrical conductivities are several orders of magnitude higher than those of "ordinary" salt crystals near the melting point. Secco has invoked a percolation-type mechanism rather than the "paddle-wheel mechanism." The electrical conductivity of solid solutions of tungstate in lithium sulfate has been suggested as a "crucial experiment" for choosing between these two mechanisms. A comparison is made of all experiments of this type performed so far for the range 2 to 50 mol% tungstate. A zoning experiment is presented in support of the Li2SO4-Li2WO4 phase diagram determined by Gunawardane et al. (Br. Ceram. Trans.J. 88, 45 (1989)). A single-crystal neutron diffraction study of fcc Li2SO4 strongly supports the paddle-wheel mechanism. © 1993 Academic Press. All rights reserved.