Phase assemblage and microstructures of Gd2Ti2-xZrxO7 (x = 0.1–0.3) pyrochlore glass-ceramics as potential waste forms for actinide immobilization

Glass-ceramics (GCs) based on titanate pyrochlores have attracted recent attention as candidate waste forms for actinide immobilization. As zirconate pyrochlore has a superior radiation resistance, it is anticipated that Zr substitution of Ti in titanate pyrochlore GCs would increase their potential for waste form applications. The concept was primarily addressed via the preparation of Gd2Ti2-xZrxO7 (x = 0.1–0.3) GCs to determine the effects of sintering temperature, Zr substitution, and pyrochlore content (50–70 wt%) on the properties of the resultant GCs. XRD and SEM analyses were used to reveal the phase assemblages and microstructures while TEM and Raman spectroscopy were used to analyze the local structures. XRD results confirmed the formation of the targeted pyrochlore as the major phase, with Gd9.33(SiO4)6O2 oxyapatite present as a minor phase. SEM analyses revealed that up to 0.2 formula units of Ti could be substituted by Zr under the processing conditions. The pyrochlore crystallite sizes were largely controlled by the sintering temperature and cooling rate and showed little sensitivity to the glass contents. This work has demonstrated successful substitutions of Ti with Zr in Gd2Ti2O7 GCs as potential waste forms for actinide wastes owing to their superior radiation resistance. The feasibility of Zr substitution of Ti in Gd2Ti2O7 glass-ceramics for improving radiation resistance of titanate pyrochlore glass-ceramics as potential composite waste forms for actinide immobilization has been investigated. It has been demonstrated that up to 0.2 formula units of Zr can replace Ti in Gd2Ti2O7 to form titanate-zirconate pyrochlore glass-ceramics with major crystalline pyrochlores and a minor Gd-silicate oxyapatite phase. [Display omitted] •Zr substitution of Ti in Gd2Ti2O7 glass-ceramics for better radiation tolerance.•Up to 0.2 formula units of Zr can replace Ti under the experimental conditions.•Phase assemblage, structure and microstructure have been investigated.•The glass-ceramics contain major pyrochlore and minor oxyapatite.