Ionic conductivity of solid calcium sulfide at 650 to 1000° C

The electrical conductivity of solid calcium sulfide has been measured at various temperatures and sulfur pressures with the aid of an alternating current bridge. At partial pressures less than about 10⁻⁶ atm at 770°C to 1000°C, the conductivity is independent of sulfur pressure and can be expressed by log₁₀ σ (Ω⁻¹ ·cm⁻¹) = −5.185/T(K) − 0.0901 The apparent activation energy for the conduction is 23.7 (± 1.04) kilocalories per mole. Both the relatively large activation energy and the lack of dependence of the specific conductivity on sulfur pressure suggest that the conduction is predominantly ionic for sulfur pressures less than about 10⁻⁶ atm. However, for pressures greater than 10⁻⁶ atm, the specific conductivity increases with an increase of the sulfur pressure, suggesting positive hole conduction. Some comments are included on the possibility of the application of calcium sulfide as a solid electrolyte of a sulfur concentration cell.