Ionic Conductivity of Pure Solid Calcium Sulfide

Abstract

Calcium sulfide disks have been carefully prepared to avoid any contamination by means of a newly-developed sintering method. The electrical conductivity has been measured at temperatures from 923 to 1173 K and in the PH2S⁄PH2 range from 0 to 102 with the aid of an alternating current bridge. Because the conductivity was independent of sulfur partial pressure, it was concluded that pure calcium sulfide is a perfect ionic conductor. The specific conductivity can be expressed as follows:log(σ⁄S·m−1)=−8.64×103⁄T+3.390 (993∼1173 K)and the apparent activation energy for the conduction is 165.3 kJ/mol.The tracer diffusivity of Ca2+ was estimated from electrical conductivity measured by using Nernst-Einstein relation. Comparing with the activation energies of self-diffusion of anions in similar crystals, it seems that the divalent calcium cation is the main charge carrier of the electrical conduction.