Phase stabilisation, thermal expansion and ionic conductivity of high content rare earth oxide (Lu₂O₃, Y₂O₃ and Gd₂O₃) stabilised cubic hafnia

For satellite propulsion, new material are developed to sustain harsh thermal and environmental conditions in the combustion chambers induced by the development of new “green” propellants less toxic than currently used hydrazine. In the present study, hafnia-based materials with different amounts and natures of stabilisers (Lu₂O₃, Y₂O₃ and Gd₂O₃) have been chosen for the ceramic part of the system. Microstructures, Thermal Expansion Coefficients (373–1673 K) and ionic conductivities (600–1273 K) of synthesised fully stabilised fluorite phases have been investigated. Lattice parameters have been determined and an abacus has been proposed as a function of the amount of RE₂O₃ and the ionic radius of the Rare Earth cation (RE³⁺). Moreover, it has been observed a TECs decrease from 14 to 40 mol% of RE₂O₃ and few changes in the ionic conductivity above 33 mol% of RE₂O₃. Finally, addition of Lu₂O₃ allows to reach the lowest TEC and ionic conductivity.