A simple piston-cylinder apparatus was developed for impedance spectroscopy at pressures up to 3 GPa and temperatures up to 500°C. The apparatus is of the compound cylinder type, with the innermost cylinder made of a commercially available low-cost alumina-based ceramic, with pistons of hard metal that allow electric connections. Cell electrical resistance was higher than 1 M⍀ at TϽ300°C and higher than 100 k⍀ at 400°C. The inductivity in the wires and pistons was about 2 H. The sample was

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... sed in a h-BN capsule, which insured a good hydrostaticity without disturbing the measurement. The equipment proved to be very useful in determining the activation volume of the conduction process in several ionic conductors.