Temperature Dependence of Hertzian Indentation Fracture Surface Energy of ThO 2

The fracture surface energy, γ, of ThO 2 was measured between room temperature and 400°C using the Hertzian indentation technique with cold or preheated steel and alumina indentors. The value of γdecreased strongly with temperature with a suggested saturation at 350°C. This may indicate the change from an unrelaxed fracture surface to a relaxed surface at temperatures where oxygen becomes mobile. The result obtained at 400°C is γ=1.4 J m −2 .