Unravelling composition-regulated phase transitions in gadolinium zirconate solid solutions by synchrotron X-ray diffraction and Raman spectroscopy

Gadolinium zirconates have been comprehensively studied as the candidate waste forms due to their high structure flexibility, excellent chemical durability and good resistance to radiation damage. They are most suitable for the waste streams containing fissile materials as gadolinium can act as an effective neutron absorber to control the potential criticality risk. Herein, we report a detailed study focusing on the composition-regulated pyrochlore to fluorite phase transitions of Gd 2 (Zr 2– x Gd x )O 7– x /2 ( x = 0–0.668, step size of ∼0.1) solid solutions prepared via a nitrate co-precipitation route and sintered at 1400 °C. A high-resolution synchrotron X-ray diffraction study confirmed the phase transitions from a highly ordered pyrochlore ( x = 0) to disordered pyrochlores (0 < x ≤ 0.208) with increasing cation disorder and then to defect fluorites ( x = 0.284–0.668), further complemented using Raman spectroscopy. The findings in this study highlight the compositional flexibility of gadolinium zirconate solid solutions and the obtained insights into composition-regulated structural evolution provide useful guidelines for developing these materials for nuclear waste form applications. • Gd 2 (Zr 2– x Gd x )O 7– x /2 ( x = 0–0.668, step size ∼0.1) was synthesised via co-precipitation and sintered at 1400 °C. • Pyrochlore–fluorite phase transitions were revealed by synchrotron XRD and Raman spectroscopy. • Gd 2 (Zr 2– x Gd x )O 7– x /2 shows compositional tunability for nuclear waste form applications. • Structural evolution offers insights into phase behaviour of Gd 2 (Zr 2– x Gd x )O 7– x /2 ceramics.