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 P_H2S⁄P_H2 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.