Structural phase transition in ZrO2 induced by swift heavy ion irradiation at high pressure

Tracks of nuclear fission fragments in minerals of the Earth's crust and upper mantle are generally used for dating these materials. These samples are mostly gathered from depths where high pressure is predominant. The influence of pressure on track formation is therefore of great interest. We realized such pressures by means of diamond anvil cells (DAC). A zirconia (ZrO2) sample was placed in the central aperture (used as sample chamber) of a metal gasket squeezed from opposite sides by two diamond anvils. To ensure hydrostatic pressure, the sample chamber was additionally filled with a pressure medium (methanol:ethanol:water 16:3:1) which solidifies at 14.5 GPa. The loaded cell was placed in front of the exit window of the SIS beamline in Cave A. To irradiate the sample, the ions require initial energies of ~ 220 MeV/u. The beam passes the Al exit window, the air gap, the first diamond (where most of the energy is deposited), penetrates the sample, and is then stopped in the second diamond. The estimated energy-loss occurring in the sample is around 35 keV/nm.