Effect of pressure on the electrical conductivities of some fused nitrates, nitrites, chlorates, perchlorates, dichromates and thiocyanates

Abstract

The pressure dependence of the electrical conductivity (κ) has been measured over the range 1–1000 bar (1 bar = 10⁵ N m^–2) at temperatures up to 420°C, for the following fused salts: LiClO₃, LiClO₄; NaNO₂, NaClO₃, Na₂Cr₂O₇; KClO₃, K₂Cr₂O₇, KSCN; AgNO₃. The volumes ΔV_κ=–RT(∂ ln κ/∂P)_T were calculated from these results. For a given cation, the value of ΔV_κ increases as the size of the anion increases and vice versa. ΔV_κ was approximately independent of temperature for some of the salts studied, but for others (notably LiClO₃ and KSCN)ΔV_κ increased steeply as the temperature was lowered. This behaviour is interpreted as being due to a rise in the glass transition temperature with pressure. An equation is proposed which allows the high-temperature limiting value of ΔV_κ to be estimated using experimental data obtained at lower temperatures.