Accurate determination of equation of state and synthesis recovery pathways in hafnia at high pressures and temperatures

The HP allotropes of Hafnia, HfO2, have attracted attention for decades because of their potential for applications ranging from hard oxide coatings to resistive-switch memories. HP experiments have reported bulk moduli up to 340 GPa for the recoverable ortho-II phase using XRD at 300K; however, this approach can lead to big uncertainties, especially for highly incompressible materials; furthermore, direct measurements of the material’s hardness are scarce, and no recovery of the HP ortho-I phase was reported. Here, we propose to use the setup at ID06-LVP to combine in situ structural and ultrasonic interferometry measurements to provide the first reliable estimation of the adiabatic bulk and shear moduli of HfO2 at HP-HT conditions. This information will be essential to assess the capabilities and opportunities for its wide-ranging applications. Furthermore, we will optimize the synthesis and recovery P-T pathways, still lacking for the ortho-I phase.