Ion irradiation effects on Ho _2+xTi _2-xO _7-x/2 (x=0, 0.4 and 0.67)

We recently synthesized different composition polycrystalline Ho _2+xTi _2-xO _7-x/2 (X=0, 0.4 and 0.67), which is derivative fluorite compounds known as a, β and pyrochlore phases in Ho ₃O ₂-TiO ₂ phase diagram by using conventional solid state synthesis methods. The samples were irradiated with 400 keV Ne ²⁺ ions at cryogenic temperature (∼77 K), using the Danfysik ion accelerator at the Ion Beam Materials Laboratory (IBML) of Los Alamos National Laboratory (LANL). The irradiation fluences in the experiments ranged from 5×10 ¹⁴-5×10 ¹⁵ ions/cm ². An order-to-disorder (O-D) transformation was observed for a, β and pyrochlore phases, as determined using grazing incidence X-ray diffraction (GIXRD) at an incident angle of 0.25°. The O-D transformation threshold fluence for a phase was found to be noticeably lower than those for β phase and pyrochlore, and the O-D transformation threshold fluence for β phase was the highest. The O-D transformation threshold fluence was found to be coherent with the phase transformation temperature in the Ho ₃O ₂-TiO ₂ temperature-composition (T-C) phase diagram.