Measurement of the principal isentropes of lead and lead-antimony alloy to ∼400 kbar by quasi-isentropic compression

The magnetic-pressure drive technique allows single-shot measurements of compression isentropes. We have used this method to measure the isentropes in the pressure-volume space of bulk and single-crystal lead, and lead-antimony alloy to similar to 400 kbar. The isentrope pressure-volume curves were found from integration of the experimentally deduced Lagrangian sound speed as a function of particle velocity. A characteristics calculation method was used to convert time-resolved free-surface velocity measurements to corresponding in situ particle-velocity histories, from which the Lagrangian sound speed was determined from the times for samples of different thicknesses to reach the same particle velocity. Use of multiple velocity interferometry probes decreased the uncertainty due to random errors by allowing multiple measurements. Our results have errors of from 4% to 6% in pressure, similar to 1% to 1.5% in volume, depending on the number of measurements, and are consistent with existing isotherm and Hugoniot data and models for lead.