Crystal chemical design principles were applied to synthesise novel U4+dominant and titanium excess betafite phases Ca1.15(5)U0.56(4)Zr0.17(2)Ti2.19(2)O7and Ca1.10(4)U0.68(4)Zr0.15(3)Ti2.12(2)O7, in high yield (85–95 wt%), and ceramic density reaching 99% of theoretical. Substitution of Ti on the A-site of the pyrochlore structure, in excess of full B-site occupancy, enabled the radius ratio (rA/rB= 1.69) to be tuned into the pyrochlore stability field, approximately 1.48 ≲ rA/rB≲ 1.78, in contrast to the archetype composition CaUTi2O7(rA/rB= 1.75). U L3-edge XANES and U4f7/2and U4f5/2XPS data evidenced U4+as the dominant speciation, consistent with the determined chemical compositions. The new betafite phases, and further analysis reported herein, point to a wider family of actinide betafite pyrochlores that could be stabilised by application of the underlying crystal chemical principle applied here.