Electric conductivity of supercritical cesium‐cesium hydride mixtures at high temperatures and pressures

<jats:title>Abstract</jats:title><jats:p>Above a critical temperature of 665° liquid cesium and nonmetallic ionic liquid cesium hydride are completely miscible. This has been demonstrated previously with high pressure phase equilibrium measurements. An equilibrium hydrogen pressure belongs to each temperature and mixture composition and is used to prepare a desired sample composition. An autoclave for high pressure hydrogen is described into which electric conductance cells can be placed. With the cylindrical cell A the sample resistance is measured parallel to the thin stainless steel walls. With cell B, the resistance is determined between two tantalum electrodes separated by alumina.</jats:p><jats:p>Conductances have been measured along seven isotherms from 550 to 800°. To cover mole fractions <jats:italic>x</jats:italic> (CsH) from 0.01 to 0.98, hydrogen pressures up to 1000 bar had to be applied. In the cesium‐rich, “metallic”, region conductances between 3000 and 9000 Ω<jats:sup>−1</jats:sup> cm<jats:sup>−1</jats:sup> were observed with negative temperature derivatives. In the cesium hydride‐rich, “ionic”, region conductances between 20 and 100 Ω<jats:sup>−1</jats:sup> cm<jats:sup>−1</jats:sup> were found with positive temperature coefficients. For the metallic region the conductance is discussed with the Mott “nearly free electron” (NFE) model in comparison with cesium‐gold and cesium‐halide systems. The NFE region extends down to 1300 Ω<jats:sup>−1</jats:sup> cm<jats:sup>−1</jats:sup> for the hydride systems. The metallic‐nonmetallic transition region extends from 1300 to 250 Ω<jats:sup>−1</jats:sup> cm<jats:sup>−1</jats:sup>. At the critical consolution point (665°, <jats:italic>x</jats:italic>(CsH) = 0.68, <jats:italic>p</jats:italic>(H<jats:sub>2</jats:sub>) = 157 bar) the conductivity is 830 Ω<jats:sup>−1</jats:sup> cm<jats:sup>−1</jats:sup>.</jats:p>